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  • Amino acids  (66)
  • Springer  (66)
  • 1990-1994  (65)
  • 1985-1989
  • 1970-1974  (1)
  • 1992  (65)
  • 1972  (1)
Collection
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  • 1990-1994  (65)
  • 1985-1989
  • 1970-1974  (1)
Year
  • 1
    ISSN: 1432-1076
    Keywords: Diet ; Pregnancy ; Amino acids ; Protein
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A 25-year-old woman with tyrosinaemia type II was treated from the 5th week of pregnancy with a protein-restricted diet supplemented with a tyrosine/phenylalanine-free amino acid mixture. Tyrosine concentrations were maintained in the range 100–200 μmol/l by restricting natural protein intake to 0.16 g/kg per 24h in early pregnancy, with increases up to 0.38 g/kg per 24h in the last trimester. This treatment maintained plasma phenylalanine concentrations in the range 20–40 μmol/l. Maternal weight gain and fetal growth were normal, and the mother remained asymptomatic throughout the pregnancy. A normal infant was born at term with length, weight and head circumference between the 25–50 th per centiles.
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  • 2
    ISSN: 1432-2285
    Keywords: Amino acids ; Populus ; Protein bodies ; Vessels ; Xylem transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The seasonal changes in the pattern of 21 amino acids occurring in the xylem vessels of Populus twigs have been studied in connection to the mobilization of protein bodies in ray parenchyma cells at the electron microscopic level. Hydrolysis of protein bodies in spring and movement of amino acids into vessels are found to be closely linked. Comprising more than 75% of total amino acid content, glutamine (Gln) is by far the dominant N-constituent of the sap. Gln reaches up to 11 μmol ml-1 in the spring sap while other amino acids only show 1/20 to 1/100 of this amount. From the measured Gln accumulation rates in the vessels in nature and in the vessels of isolated shoots, a minimum flux rate for Gln of 5.6 pmol cm-2 min-1 is calculated for the ray contact cell/vessel interface. Furthermore, because Gln constitutes 75% of the amino acid content of the sap but only 1.3% of the amino acids in the 32 kDa storage protein of the ray cells in the wood (Clausen and Apel 1991), it becomes evident that most amino acids originating from protein body mobilization do not enter the vessels but are used for Gln synthesis preceding Gln release into the vessels.
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  • 3
    ISSN: 1432-2242
    Keywords: Amino acids ; Cytoplasmic male sterility ; Petunia ; Transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Two pairs of isonuclear lines of cytoplasmic male-sterile (CMS) and fertile (F) petunia cells grown in suspension culture in the presence or absence of amino acid sources were examined for uptake of 11 amino acids and adenosine. Cells from CMS lines exhibited a significant lower rate of uptake than F cells. These differences, for various amino acids, are a result of lower affinity (high Km) values and of lower maximal velocities. Although the uptake of most of the amino acids examined was affected by the availability of energy in the cell, the differences in uptake seem to be less dependent on the energy status of the cell.
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  • 4
    ISSN: 1432-0789
    Keywords: Urease production ; Soil microorganisms ; Ammonium ; Nitrate ; Amino acids ; Nitrogen assimilation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Studies of the effects of different forms of N on urease production in soils amended with organic C showed that although microbial activity, as measured by CO2 production, was stimulated by the addition of NH4 + or NO3 - to C-amended soils (200 μmol glucose-C g−1 soil), urease production was repressed by these forms of N. The addition of L-methionine sulfoximine, an inhibitor of inorganic N assimilation by microorganisms, relieved the NH4 + and NO3 - repression of urease production in C-amended soil. The addition of sodium chlorate, an inhibitor of NO3 - reduction to NH4 + by microorganisms, relieved the NO3 - repression of urease production, but did not eliminate the repression associated with NH4 +. These observations indicate that microbial production of urease in C-amended soils is not directly repressed by NH4 + or NO3 -, but by products formed by microbial assimilation of these forms of N. This conclusion is supported by our finding that the biologically active L-isomers of alanine, arginine, asparagine, aspartate, and glutamine, repressed urease production in C-amended soil, whereas the D-isomers of these amino acids had little or no influence on urease production. This work suggests that urease synthesis by soil microorganisms is controlled by the global N regulon.
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  • 5
    ISSN: 1432-069X
    Keywords: Sphingolipids ; Ceramide ; Scaly skin ; Amino acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Stratum corneum sphingolipids are of particular importance in maintaining the water permeability barrier of mammalian epidermis. Free amino acids also play an important role in water retention in the stratum corneum. To clarify the way in which these substances affect scaly skin, stratum corneum sphingolipids and free amino acids collected from artificially-induced scaly skin were analysed. Scaly skin was induced by tape stripping. The total amount of sphingolipids was quantified by gas chromatography and five of sphingolipid fractions were isolated and quantified by thin-layer chromatography. Free amino acids were analysed using a high-speed amino analyser. The total amount of sphingolipid in scaly skin did not differ statistically from that in control skin. However, a significant change in the distribution of the five sphingolipid species was observed in scaly skin and the total amount of amino acids was decreased in scaly skin. These results suggest that the distribution of these five types of sphingolipid and the total amount of amino acids are responsible for scaly skin.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Archives of microbiology 158 (1992), S. 256-261 
    ISSN: 1432-072X
    Keywords: Frankia ; Amino acids ; Glutamine synthetase ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The utilization of some amino acids, added at 1 mM and 10 mM concentrations, as the sole combined nitrogen sources by Frankia sp. strain CpI1, has been investigated. Glutamine, like NH 4 + , provided rapid growth without N2 fixation. Histidine at 1 mM yielded poor N2-fixing activity but better cell growth than N2. Aspartate, glutamate, alanine, proline, each at 1 mM concentration, supported similar levels of N2 fixation and growth. Growth on 10 mM glutamate, proline, or histidine resulted in poor N2-fixing activity and poor cell growth. Cells grown on 10 mM alanine had about half the N2-fixing activity of cells grown on N2 but growth was good. Aspartate at 10 mM concentration, however, stimulated N2-fixing activity dramatically and promoted faster growth. Enzyme analysis suggested that asparate is catabolized by glutamate-oxaloacetate transaminase (GOT), since GOT specific activity was induced, and aspartase activity was not detected, in cells grown on aspartate as the sole combined nitrogen source. Thinlayer chromatography (TLC) of metabolites extracted from N2-grown cells fed with [14C]-aspartate showed that label was rapidly accumulated mainly on aspartate and/or glutamate, depending on the cells' physiological state, without detectable labeling on fumarate or oxaloacetate (OAA). These findings provide evidence that aspartate is catabolized by GOT to OAA which, in turn, is rapidly converted to α-ketoglutarate through the TCA cycle and then to glutamate by GOT or by glutamate synthase (GOGAT). The stimulation of N2 fixation and growth by aspartate is probably caused by an increased intracellular glutamate pool.
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  • 7
    ISSN: 1432-1351
    Keywords: Lobster ; Antenna ; Chemoreceptor organs ; Amino acids ; Concentration dependent tuning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. We determined the spectral tuning properties of 47 chemoreceptor cells of the antenna of Homarus americanus to amino acids and other compounds. Tests with 17 single compounds at 10-4 M showed 40 of 47 cells responded best to hydroxyproline, 4 cells to taurine and 3 cells to betaine. Mean tuning breadth (H-metric) doubled with 10 fold increase in concentration. 2. In hydroxyproline-best cells the mean threshold for hydroxyproline (Hyp) was found between 10-7 M and 10-8 M. An equimolar mixture of the 17 compounds generated a shallower stimulus-response function with thresholds similar to Hyp function (mixture suppression). Hyp-best cells were relatively narrowly tuned, often with arginine or leucine as second best stimuli. 3. Thus, physiologically the second antenna of H. americanus is a major chemoreceptor organ. It is more than any of the 5 chemoreceptor organs studied so far dominated by a single best-cell type (Hyp). Receptor cell composition of antennae resembles that of antennules more than legs or maxillipeds. Hyp-best cells in antennae and lateral antennules have similar tuning spectra. 4. Our cell tuning studies argue for independent receptors for all amino acids tested. We conclude that diversity of receptor cell tuning is created by cell-specific blends of receptors. At the organ level, differences in organ tuning result from different blends of receptor cells.
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  • 8
    ISSN: 1432-1939
    Keywords: Nectar ; Sugar ; Amino acids ; Preferences ; Ornithoptera priamus poseidon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Preferences for nectar sugars and amino acids ofOrnithoptera priamus butterflies were tested experimentally. Both male and female butterflies clearly preferred a sucrose solution over a glucose solution of equal concentration (25%, weight to total weight) and equally a fructose solution over a glucose solution. A significant trend of males to prefer fructose over sucrose and of females to prefer sucrose over fructose was detected. However, neither males nor females discriminated between a mimic ofLantana camara nectar containing amino acids and a corresponding plain sugar solution. These results suggest that butterflies select against glucose in floral nectar but do not support the hypothesis that butterflies select for high levels of amino acids in nectar. The rather unspecific response ofOrnithoptera priamus butterflies to the tested nectar constituents may reflect a generalist feeding strategy of these long-lived and spectacular butterflies.
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  • 9
    ISSN: 1432-2072
    Keywords: 5-HT release ; 5-HT synthesis ; Amino acids ; l-tryptophan ; l-valine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract l-Valine competes with tryptophan for transport into the brain and has previously been shown to decrease brain 5-HT synthesis. In the present study, the effect ofl-valine on electrically evoked hippocampal 5-HT release was determined in the anaesthetized rat using microdialysis. In control animals two electrical stimulations of the dorsal raphe nucleus 120 min apart (S1 and S2, respectively) released similar amounts of 5-HT. In contrast, in animals which receivedl-valine (200 mg/kg) between stimulations, S2 released a significantly smaller amount of 5-HT than did S1, although basal 5-HT release was unchanged. The data demonstrate thatl-valine decreases the electrically-evoked release of 5-HT in hippocampus in vivo.
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  • 10
    ISSN: 1573-1561
    Keywords: Amino acids ; Solanum tuberosum ; Leptinotarsa decemlineata ; Coleoptera ; Chrysomelidae ; Empoasca fabae ; Homoptera ; Cicadellidae ; feeding damage
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Feeding by Colorado potato beetles and artificial defoliation had a minor effect on the profile of amino acids in potato foliage, whereas feeding by potato leafhoppers caused an increase in about one half of the amino acids measured.
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  • 11
    ISSN: 1439-6327
    Keywords: Amino acids ; Carbohydrate feedings ; Free fatty acids ; Fatigue ; Serotonin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Brain serotonin (5-hydroxytryptamine, 5-HT) has been suggested to be involved in central fatigue during prolonged exercise. Changes in the ratio of plasma free tryptophan (free Trp) to branched-chain amino acids (BCAA) are associated with altered brain 5-HT synthesis. The purposes of this study were to describe systematically the effects of prolonged exercise on changes in plasma free Trp and BCAA and to examine the effects of carbohydrate (CHO) feedings on these same variables. Eight well-trained men [ $$\dot V{\text{O}}_{\text{2}} $$ max = 57.8 (SE 4.1) ml kg−1 min−1] cycled for up to 255 min at a power output corresponding toVO2 at lactate threshold (approximately 68%VO2max) on three occasions separated by at least 1 week. Subjects drank 5 ml kg−1 body wt−1 of either a water placebo, or a liquid beverage containing a moderate (6% CHO) or high (12% CHO) concentration of carbohydrate beginning at min 14 of exercise and every 30 min thereafter. Exercise time to fatigue was shorter in subjects receiving placebo [190 (SE 4) min] as compared to 6% CHO [235 (SE 10) min] and 12% CHO [234 (SE 9) min] (P〈0.05). Glucose and insulin decreased in the placebo group, and free Trp, free-Trp/BCAA, and free fatty acids increased approximately five- to sevenfold (P 〈 0.05). These changes were attenuated in a dose-related manner by the carbohydrate drinks. Plasma free Trp and plasma free fatty acids were highly correlated (r=0.86,P〈0.001). Plasma BCAA did not change in the placebo group, but decreased slightly in those receiving 6% CHO and 12% CHO (P〈0.05). No differences in heart rate, $$\dot V{\text{O}}_{\text{2}} $$ , plasma volume and respiratory exchange ratio were found. The results indicate that free Trp and free Trp/BCAA increase progressively during prolonged cycling to fatigue. This response was attenuated by CHO feedings. Changes in plasma free fatty acids probably play a prominent role in these responses.
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  • 12
    ISSN: 1572-8927
    Keywords: Amino acids ; degree of dissociation ; electrolyte solution ; equivalent conductivity ; pK 1 ; thermodynamic dissociation constant
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The dissociation constants of amino acids are generally determined by acid-base titration and by the emf method. The use of the conductimetric method to obtain pK for amino acids appears to be the first of its kind. In this study, we describe the method of measurement, the treatment of the data and discuss the results. The choice of MOPSO for the investigation is in conjunction with the development of new buffer systems as pH Standard Reference Materials. The value for pK at 25°C is 0.060±0.005.
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  • 13
    ISSN: 1476-5535
    Keywords: Monascus ; Water-soluble pigments ; Semi-synthesis ; Amino acids ; Natural food color
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary New water-soluble red pigments were produced byMonascus sp. in a chemically defined fermentation medium containing glutamate as nitrogen source. They were isolated and characterized as glutamate derivatives of the well-known orangeMonascus pigments (monascorubrin and rubropunctatin). The new pigments have several advantages over the known redMonascus pigments (rubropunctamine and monascorubramine) including very high water-solubility, higher absorption coefficient, and greater resistance to decoloration by light. Adding glutamate, glycine or leucine to a resting-cell system led to the formation of specific water-soluble red pigments corresponding to the exogenous amino acid. The water-soluble red pigments produced by resting-cells have retention times identical to those of the corresponding red derivatives made chemically from the orange pigments in methanol-phosphate buffer at pH 7. The hydrophobicities of the amino acid sources correspond to the HPLC retention times of the red pigments derived from them.
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  • 14
    ISSN: 1573-5117
    Keywords: Amino acids ; mineralization ; bacterial community ; kinetic ; fertilized pond
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Bacterial degradation of a high concentration of amino acids (up to 150 mg l−1), released by quail manure pellets, was studied in a fertilized fish pond. Aspartic acid, Glutamic acid and Alanine were major components of the free amino acid pool (respectively 14.6%, 16.4% and 11.1%). Laboratory experiments showed a fast decomposition of these three amino acids. The degradation was a zero order reaction. Activation energy, Ea, was of the same order for the three amino acids (from 64.2 to 70.3 kg-mol−1). There was no significant difference between the behaviour of aspartic acid in the presence or not of other carbon and nitrogen supply, but stimulation of degradation of glutamic acid and of Alanine by NH4 + and C, was marked. This process may be important in the initial mineralisation of the fertilizer in fish ponds.
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  • 15
    ISSN: 1573-6903
    Keywords: Amino acids ; estrous cycle ; GABA ; glutamate ; estradiol ; progesterone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Concentrations of 11 amino acids, including the neurotransmitters GABA, glutamate, aspartate, glycine and taurine, were determined in 12 brain regions of female rats during different stages of the estrous cycle. In addition, amino acids and sex hormone levels were determined in plasma. All sample collections were done in the forenoon between 9 and 11 a.m. Most regional amino acid levels measured did not change signficantly during estrous cycle, but significant alterations were found for GABA and glutamate in hypothalamus. Both amino acids were slightly decreased in hypothalamus during proestrus, which might reflect an alteration of GABA turnover in response to the high estrogen levels during this stage. A decreased glutamate level during proestrus was also found in thalamus, while both glutamate and GABA did not vary throughout estrous cycle in any of the other examined regions, including substantia nigra, amygdala, striatum, cortex and hippocampus. When diestrus was subdivided according to progesterone levels, high levels of this hormone seemed to be associated with effects on metabolism of certain amino acids, including glycine in substantia nigra, alanine in thalamus and threonine in pons/medulla. However, the few changes in regional amino acid concentrations found during the estrous cycle were so small that the functional significance of these changes cannot be ascertained without further determination of the cellular or subcellular compartments of brain tissue involved.
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  • 16
    ISSN: 1438-2199
    Keywords: Amino acids ; Excitatory amino-acid ; NMDA ; Dopamine ; Striatum ; In vivo voltammetry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In vivo voltammetry was used in freely moving rats to study the processes whereby striatal dopamine (DA) release is regulated by corticostriatal glutamatergic neurons. Electrical stimulation of the cerebral cortex was found to markedly increase the striatal DA-related voltammetric signal amplitude. Similar enhancements have been observed after intracerebroventricular administration of 10nmoles glutamate, quisqualate and AMPA, whereas NMDA was found to decrease the amplitude of the striatal signals. The NMDA receptor antagonist APV did not significantly affect the voltammetric signal but prevented the NMDA-induced depression of the DA-related signals. These data are in agreement with those obtained in numerous previous studies suggesting that the glutamatergic corticostriatal neurons exert activatory effects on the striatal DA release via non-NMDA receptors. The mechanism involved might be of a presynaptic nature. The role of the NMDA receptors may however consist of modulating the dopaminergic transmission phasically and in a depressive way, which would be consistent with behavioural data suggesting the existence of a functional antagonism between the activity of the corticostriatal glutamatergic and nigrostriatal dopaminergic systems.
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  • 17
    ISSN: 1438-2199
    Keywords: Amino acids ; Uremia ; Acid-base ; Plasma amino acids ; Anorexia ; Glucocorticoids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Acidosis is a common finding in uremia. We analysed the effect of changes in acid-base balance in 42 Sprague-Dawley rats having longstanding uremia (〉 3 mon). The rats were treated with CaCO3 or CaCl2 in a random cross-over trial after being divided into two dietary groups (8% or 18% protein). At the end of each observation period parameters were assessed. The main finding was that plasma amino and keto acid concentrations varied significantly with the acid-base balance and the protein intake. Furthermore a considerable degree of catabolism and anorexia was observed. In addition other confounding variables were observed, e.g. increased corticosterone excretion, electrolyte losses, and proteinuria. Our data underline that plasma amino acid concentrations in uremic rats are highly dependent on acid-base balance and overall protein intake.
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  • 18
    ISSN: 1438-2199
    Keywords: Amino acids ; Liver cirrhosis ; Ornithine-aspartate ; Long-term treatment ; Urea synthesis rate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The effectiveness of ammonia reducing amino acids on hyperammonemia and hepatic encephalopathy is well known in patients suffering from liver cirrhosis. Data concerning long-term therapy on hepatic function and urea synthesis rate (UNSR) are still lacking. According to Vilstrup/Poulsen it is a good standard for functioning liver mass. Therefore, 25 patients with histologically proven liver cirrhosis and distinct portal hypertension were treated daily with 9 gr. ornithinasparte over 13 years (8–20 years). Shunt operations, esophageal varicosis sclerosis, or portal pressure reducing medication were not applied. Rigorous alcohol abstinence and 60 gr protein/day were prescribed. During the investigation, 3 laparoscopies and 4 liver biopsies were performed, on the average, on each individual. Significant improvements of clinical and biochemical results (Child-Pugh-Index; Composite Clinical and Laboratory Index) were obtained during the long-term therapy with ornithine-aspartate. Esophageal varicosis II–III was either reduced to 0-I or totally eliminated. Also significant was an increased urea synthesis rate and a decreased hyperammonemia. A plausible explanation for the long-term therapy effectiveness with ornithine-aspartate is the possible recovery of the functioning mass without hepatic size increase. Also important is the rigorous alcohol abstinence. It leads to a significant reduction of portal hypertension in patients suffering from alcohol induced liver cirrhosis (Reynolds, own observations). Additional favorable factors are intensive muscle training and absence of gastrointestinal bleeds.
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  • 19
    ISSN: 1438-2199
    Keywords: Amino acids ; Reversed-phase high performance liquid chromatography ; DABS-Amino acids ; Narrow-bore columns ; Amino and imino acid analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In this paper we report the complete separation of amino acids as DABS-derivatives using a 3µm Supelcosil LC-18 (25 cm × 2.1 mm I.D.) narrowbore column. The system described makes it possible to perform the analysis of DABS-amino acids with a sensitivity to the femtomole level. We have also studied the conditions necessary for using the narrow-bore columns for routine analysis, paying particular attention to the problem of providing adequate protection for the analytical column. We have found it very suitable to use a (2 cm × 2.1 mm I.D.) guard column filled with a 40µm Pelliguard LC-18, pellicular packing resin, without affecting the complete resolution of the DABS-amino acids. Comparing the results obtained using conventional HPLC columns (3–5µm Supelcosil LC-18) of different lengths (15 and 25 cm × 4.6 mm I.D.) with those obtainable with the narrow-bore columns used in this work, it is possible to achieve a much greater sensitivity using the narrow-bore columns. In short, using the appropriate guard column and the “standard” HPLC apparatus used, the narrow-bore columns are very useful for routine analyses of DABS-amino acids with a sensitivity at the femtomole level.
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  • 20
    ISSN: 1438-2199
    Keywords: Amino acids ; NG-Nitro-L-arginine ; High performance liquid chromatography ; Endothelium-derived relaxing factor ; Blood pressure ; Conscious dogs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Haemodynamic changes after oral administration of 30 mg/kg NG-nitro-L-arginine (L-NNA) were studied in conscious chronically instrumented mongrel dogs throughout a 24 h observation period in order to evaluate the long-term efficacy of L-NNA-induced inhibition of endothelium-dependent relaxation and its relation to plasma L-NNA level. Diastolic blood pressure remained elevated for the entire 24 h observation period, but systolic blood pressure was raised only up to the 6 h value. The hypertensive response was accompanied by bradycardia. The increase in blood pressure and the plasma L-NNA level both reached their maxima at 3 h. The plasma L-NNA level at the end of the observation period was diminished by only 21.7% with respect to the maximum increase, whilst the maximum increase in mean arterial blood pressure was attenuated by 72.2% at 24 h. These data show a dissociation between plasma L-NNA level and the respective blood pressure.
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  • 21
    ISSN: 1438-2199
    Keywords: Amino acids ; Domoic acid ; Toxic mussels ; Toxic synergism ; Excitatory amino acids ; Biotoxins ; Environmental neurotoxins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A recent episode of human intoxication by cultured mussels containing a rare excitatory amino acid named domoic acid, received particular attention for its neurological implications. The intoxication produced neurological problems, such as headache, confusion, and loss of memory, particularly severe at times. Neuronal damage was found in the hippocampus and amygdala of four patients. We now report that in neuronal cultures the neurotoxicity of a domoic acid-containing mussel extract is the result of domoic acid potentiation of the excitotoxic effect of glutamic acid and aspartic acid present in high amounts in mussel tissue. Moreover, we show that subtoxic concentrations of domoic acid are sufficient to potentiate glutamic acid and aspartic acid neurotoxicity. We present evidence suggesting that the neurotoxic synergism may be due to a reduction of Mg+ + block at the NMDA receptor-associated channel, following activation of NON-NMDA receptors by domoic acid.
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  • 22
    ISSN: 1438-2199
    Keywords: Amino acids ; Aminooxyacetic acid ; Neostriatum ; Kynurenic acid ; N-Methyl-D-aspartic acid ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The endogenous tryptophan metabolite quinolinic acid elicits in rodent brain a pattern of neuronal degeneration which resembles that caused by L-glutamate. Its qualities as a neurotoxic agent raised the hypothesis that quinolinic acid might be involved in the pathogenesis of human neurodegenerative disorders. Kynurenic acid, another endogenous tryptophan metabolite and preferential N-methyl-D-aspartate (NMDA) antagonist, has been shown to block quinolinic acid neurotoxicity. Here we report that microinjections of aminooxyacetic acid (AOAA), an inhibitor of kynurenine transaminase and of other pyridoxal phosphate-dependent enzymes, into the rat striatum produce neuronal damage resembling that caused by quinolinic acid. AOAA-induced striatal lesions can be prevented by kynurenic acid and the selective NMDA antagonist 2-amino-7-phosphonoheptanoic acid. These results suggest that AOAA produces excitotoxic lesions by depleting brain concentrations of kynurenic acid (inhibition of synthetic enzyme) or due to impairment of intracellular energy metabolism (depletion of cell energy resources). The concept of deficient neuroprotection due to metabolic defects might help to clarify the pathogenesis of human neurodegenerative disorders and to develop strategies that may be useful in their treatment.
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  • 23
    ISSN: 1438-2199
    Keywords: Amino acids ; S-Farnesyl ; Cysteine ; HPLC ; Separation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary S-trans, trans-farnesyl-L-cysteine methylester, a post translational modified amino acid, was synthesized from farnesyl bromide and L-cysteine methylester hydrochloride salt in the presence of triethylamine. Its purification as well as separation from the other isomers by HPLC on RP Vydac C4 and C8 columns are reported here.
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  • 24
    ISSN: 1438-2199
    Keywords: Amino acids ; Multibacillary leprosy ; Diet therapy ; Multidrug-therapy ; Tryptophan ; Serotonin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Deoxyfructosylserotonin (DFS), a stable derivative of serotonin, was shown to have an anti-leprosy effect (Mester and Antia). Therefore, a tryptophan-enriched food (NAL) was devised to increase the concentration of free tryptophan as serotonin precursor in blood. 32 multibacillary lepromatous leprosy patients were divided in 3 groups receiving: 1) MDT (multi-drug therapy, control — 8 patients), 2) NAL (50 g/day — 13 patients) and 3) NAL + 1/2 MDT (11 patients). The clinical improvement (clinical score) was 24.2% for 1), 19.9% for 2) and 30.4% for 3). The loss of viability of theM. leprae bacilli in the mouse foot-pad test was 66% for 1), 75% for 2) and 70% for 3). The improvement by serodiagnosis (ELISA) was 19.4% for 1), 25.1% for 2) and 23.3% for 3). These preliminary results (6 months) suggest that the NAL-food is efficient against leprosy and apparently not very different from the control MDT in that respect.
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  • 25
    ISSN: 1438-2199
    Keywords: Amino acids ; High-performance liquid chromatography ; o-Phthaldialdehyde ; N-Isobutyryl-cysteine ; D-Amino acids ; Food ; Toxicology ; Nutrition ; D-Amino acid oxidase ; Microorganisms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Free L- and D-amino acids (L-AA, D-AA) were isolated from an Appenzeller cheese, from raw milk, and from an ethanolic extract as well as a total hydrolysate of cow's rumen microorganisms, and their relative amounts were determined by reversed-phase high-performance liquid chromatography after derivatization witho-phthaldialdehyde together withN-isobutyryl-L-(or D)-cysteine. D-Ala, D-Asp and D-Glu were found, among other D-AA in all cases and a microbial origin of free D-AA found in cheese and milk was rationalized. From the results, and taking other findings of the occurrence of D-AA in food and beverages into account, the highest intake of D-AA is to be expected from the consumption of ripened cheeses. From the presence of D-amino acid oxidases in human kidney, liver, and brain and from reports on the intravenous administration of racemic AA to humans and their metabolisation it is concluded that intake of free D-AA found in food is no threat for human beings.
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  • 26
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    Amino acids 2 (1992), S. 289-296 
    ISSN: 1438-2199
    Keywords: Amino acids ; C-terminal peptide ; Thiohydantoin derivatives ; C-terminal sequencing ; Solid phase peptide sequencing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary C-terminal amino acid sequence analysis seemed to be established procedure, as the counterpart of Edman's N-terminal sequencing method. However, poor recovery of the C-terminal amino acids in the reaction in homogeneous solution suggested further improvement of the method. In the present study, N-terminal amino acid was fixed covalently to the controlled pore glass (CPG) beads and the C-terminal amino acid was activated (by treating with acetic anhydride), coupled with thiocyanate to form thiohydantoin (TH) ring at the C-terminus. Then, the C-terminal amino acid was split off as the corresponding TH derivative, and analyzed by HPLC. Hydrolysis of the TH derivative was achieved at 60°C in the presence of 2 M HC1 for 2 h. Solid phase fixed peptide was washed simply with acetone, and dried for the next cycle of the reaction. So far obtained results in the heterogeneous mixture are not satisfactory in terms of the recovery of the C-terminal TH, and improvement of the recovery and further steps are under progress.
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  • 27
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    Amino acids 3 (1992), S. 1-23 
    ISSN: 1438-2199
    Keywords: Amino acids ; Computers ; Inborn errors of metabolism ; Models ; Protein synthesis ; Software ; Systems analysis ; Urea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary This article briefly summarises various aspects of building a model, before reviewing some models of protein turnover, the metabolism of selected amino acids, and urea synthesis in human subjects. Some software for use in modelling is noted. An Appendix lists terms with descriptions and definitions, which are often employed in modelling.
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  • 28
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    Amino acids 3 (1992), S. 25-52 
    ISSN: 1438-2199
    Keywords: Amino acids ; Radiation toxicity ; Radioprotection ; Thiols ; Free radicals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Numerous amino acids and their analogs are capable of protecting biological systems from the toxic effects of ionizing radiation. These radioprotective agents can be classified into two broad groups, depending upon the presence or absence of a free or potentially free sulfhydryl group. The sulfhydryl-containing compounds have been studied extensively and are thought to exert their radioprotective effects by several mechanisms, including free radical scavenging and hydrogen atom donation. Several non-sulfhydryl-containing amino acids are also being investigated for their radioprotective effects. These agents are less well known than the familiar sulfhydryl compounds, but possess very interesting protective qualities. In short, the study of amino acids and their derivatives as radioprotective agents continues to contribute to an understanding of processes involved in radiation toxicity and to offer new compounds with potential application to situations of human exposure.
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  • 29
    ISSN: 1438-2199
    Keywords: Amino acids ; Schiff bases ; Kinetics ; Pyridoxal 5′-phosphate ; Vitamin B-6 group
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Stability of Schiff bases from Pyridoxal-5′-phosphate andα- and nonα-amino acids and amines have been studied in a wide range of pH. Furthermore the transamination process for the PLP-serine Schiff base and the cyclization reaction of PLP-histidine Schiff base have also been studied. Results show that theα-position on carboxyl group of amino acids plays an important role on the mechanism of hydrolysis of imine bond. Absence of ionic groups in the surroundings of that bond seems to be an important fact of stability. In the transamination reaction, the rate-determining step is the isomerization of the Schiff base to ketoimine, since the rate constants for disappearance of Schiff base coincide with the rate constants for PMP formation. This process is catalyzed by the OH−/H2O system and the monoprotonated amino acid.
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  • 30
    ISSN: 1438-2199
    Keywords: Amino acids ; Tritium NMR ; Tritium-labelled amino acids-Tritium-labelled peptides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A method has been developed for the qualitative and quantitative analysis of complex isotopic mixtures of tritium-labelled amino acids and peptides by using high resolution3H NMR spectroscopy at 266.8 MHz. Determined were tritium distribution in alanine, glycine, tryptophan and 4-hydroxyproline amino acids, as well as in glycine and valine residues of peptides. Approaches have been worked out for the determination of spin coupling constants and isotope chemical shifts for the strongly coupled nonequivalent atoms of the methylene groups.
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  • 31
    ISSN: 1438-2199
    Keywords: Amino acids ; Conditioned avoidance ; Discrimination ; Nerve impulses ; Dopamine ; Excitatory amino acids ; Amphetamine ; Phencyclidine (Rat)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Rats were trained to perform a conditioned avoidance response to white noise in a conventional two-compartment “shuttle-box”. The partition between the compartments had two openings, however, and the correct passage (leftor right) was signalled by changes in background illumination. In this situation the psychotomimetic compoundsd-amphetamine (4 mg kg−1 IP) and phencyclidine (PCP) (2 mg kg−1 SC) were found to selectively disrupt the visual discrimination. Thed-amphetamine-induced abnormal behavior in this situation has previously been linked to excessive dopamine (DA) receptor stimulation, not controlled by nerve impulse flow and its regulation by important local feed-back mechanisms. Thus, the psychotomimetic effects produced by this compound should not only by due to increased DA receptor activationper se, but also to a disruption of normal patterns of firing and release in dopaminergic neurons. There is evidence to suggest that PCP via an excitatory amino acid (EAA) receptor produces a similar net effect on brain meso-limbic dopaminergic neurotransmission via an increased rate of firing, accompanied by regularization of firing (loss of burst activity). In support for a mediation of PCP-induced effects via EAA receptors, the local application of kynurenic acid into the ventral forebrain (4.7µg, bilaterally) was found also to produce a selective disruption of discriminative performance. It should be noted, however, thatd-amphetamine-induced loss of discriminative behavior, but not that induced by PCP, was antagonized by haloperidol (0.1–0.2 mg kg−1 IP) administration. It is thus possible that at least some effects of PCP in this situation are mediated on the efferent side of the dopaminergic neuron. It is suggested that the abnormal behavior, as evidenced by a loss of discriminative (but not avoidance) behavior, is due to disruption of normal, feed-back regulated, nerve impulse flow.
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  • 32
    ISSN: 1438-2199
    Keywords: Amino acids ; Neocortex ; GABA ; Kindling ; Rabbits
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary To investigate how GABAergic function affects seizure development, the effects of a GABA antagonist, bicuculline, on neocortical and hippocampal kindling were examined in chronically prepared rabbits. Kindling-inducing stimulations consisted of stimulus trains repeated at 5-min interstimulus intervals to produce so-called “rapid kindling”. The changes in after-discharge (AD) durations induced by each of 15 trials of stimulus trains per session were compared before and 30 min after i.p. injection of bicuculline solution (2 mg/kg) in each of three kindling groups consisting of 5 rabbits each, i.e. visual cortical, motor cortical and hippocampal kindling groups. In the visual cortex and to a less extent, the motor cortex kindling groups, the AD durations were shortened after bicuculline injection and did not show the progressive prolongation seen before the injection. In contrast, the hippocampal kindling group showed a further marked prolongation of the AD durations after the injection. The bicuculline-induced blockade of neocortical kindling suggests facilitative GABAergic action on seizure development, while the drug-induced enhancement of hippocampal kindling reflects the known inhibitory GABAergic action.
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  • 33
    ISSN: 1438-2199
    Keywords: Amino acids ; Osmolytes ; Dehydration ; Rat ; Taurine ; Myoinositol ; Sorbitol ; Betaine ; Glycerophosphorylcholine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary During antidiuresis cells in the renal inner medulla contain large amounts of sorbitol, myo-inositol, glycerophosphorylcholine and betaine to adjust the intracellular osmolality to the extracellular hyperosmolality. Although the accumulation of these four major organic osmolytes in the inner medulla of the dehydrated animal has been a consistent finding, the role of another class of organic osmolytes, amino acids, in osmoregulation in the kidney remains controversial. In the present study, renal responses of four major osmolytes and amino acids to dehydration were investigated using two HPLC systems. Taurine levels were significantly higher in the inner medulla of the dehydrated rats as compared with the control rats, and increased monotonically from the cortex to the inner medulla along the corticopapillary axis in the dehydrated rats. As for four major osmolytes, we confirm previously reported patterns in antidiuresis in greater detail. In conclusion, not only the four major osmolytes but taurine also plays a salient role in the osmoregulation in the kidney.
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  • 34
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    Amino acids 2 (1992), S. 1-12 
    ISSN: 1438-2199
    Keywords: Amino acids ; Purified diets ; Minerals ; Vitamins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Chemically defined amino acid diets have been developed for most laboratory and meat-producing animal species as well as for humans. In many cases, growth performance of animals fed these diets equals that obtained with standard intact-protein diets. The pattern of both essential and nonessential amino acids is critical to obtaining excellent voluntary food intake. Other factors such as carbohydrate and fat type and level, acid-base balance (i.e., cation-anion ratio), and texture are important to the success of purified diets. Chemically defined diets provide amino acids, mineral elements and vitamins in forms that are maximally bioavailable. Also, virtually any nutrient can be manipulated at will for studies of a) requirements, b) bioavailability, c) factors affecting requirements and bioavailability, d) nutrient-nutrient interrelationships, e) nutrientdrug or nutrient-toxin interrelationships, f) absorption phenomena and g) efficiency and priority aspects of nutrient utilization. Requirements for essential nutrients are generally lower with purified diets than for practical diets because the nutrients in the former are more bioavailable, but also because purified diets generally lack antagonizing factors such as phytate and soluble fiber. That chemically defined diets for pigs, rats and dogs yield such excellent rates of growth suggests that a specific peptide requirement many not exist for these species. Also, this suggests that all known nutrients necessary for maximal growth must be present in the diet. Whether additional nutrients, or different levels, may be necessary for optimal health and immunocompetency, or for maximal life span, needs further study.
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  • 35
    ISSN: 1438-2199
    Keywords: Amino acids ; Inborn errors of metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Disorders of amino acid metabolism or transport are most clearly expressed in urine. Nevertheless the interpretation of abnormalities in urinary amino acid excretion remains difficult. An increase or decrease of almost every amino acid in urine can be due to various etiology. To differentiate between primary and secondary aminoacido-pathies systematic laboratory investigation is necessary. Early diagnosis of disorders of amino acid metabolism or transport is very important, because most of them can be treated, leading to the prevention of (further) clinical abnormalities. In those disorders, which cannot be treated, early diagnosis in an index-patient may prevent the birth of other siblings by means of genetic counseling and prenatal diagnosis. Primary aminoacidopathies can be due to genetically determined transport disorders and enzyme deficiencies in amino acid metabolism or degradation. Secondary aminoacidopathies are the result of abnormal or deficient nutrition, intestinal dysfunction, organ pathology or other metabolic diseases like organic acidurias. A survey of amino acid metabolism and transport abnormalities will be given, illustrated with metabolic pathways and characteristic abnormal amino acid chromatograms.
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  • 36
    ISSN: 1438-2199
    Keywords: Amino acids ; Asymmetric synthesis ; α-Aminophosphonic acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The enantiospecific synthesis of severalα-aminophosphonic esters starting from enantiomerically pure derivatives of phosphonic analogues of homoserine is reported.
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  • 37
    ISSN: 1438-2199
    Keywords: Amino acids ; Dopamine ; Acetylcholine ; Glutamate ; Aspartate ; Gamma-aminobutyric acid (GABA) ; Striatum ; Microdialysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The neuronal origin of extracellular levels of dopamine (DA), acetylcholine (ACh), glutamate (Glu), aspartate (Asp) and gamma-aminobutyric acid (GABA) simultaneously collected from the neostriatum of halothane anaesthetized rats with in vivo microdialysis was studied. The following criteria were applied (1) sensitivity to K+-depolarization; (2) sensitivity to inhibition of synaptic inactivation mechanisms; (3) sensitivity to extracellular Ca2+; (4) neuroanatomical regionality; sensitivity to selective lesions and (5) sensitivity to chemical stimulation of the characterized pathways. It was found that: (1) Extracellular DA levels found in perfusates collected from the neostriatum fulfills all the above criteria and therefore the changes in extracellular DA levels measured with microdialysis reflect actual release from functionally active nerve terminals, and so reflect ongoing synaptic transmission. (2) Changes in neostriatal ACh levels reflect neuronal activity, provided that a ACh-esterase inhibitor is present in the perfusion medium. (3) Extracellular Glu, Asp and GABA could be measured in different perfusion media in the rat neostriatum and probably reflect metabolic as well as synaptic release. However, (4) the majority of the extracellular GABA levels found in perfusates collected from the neostriatum may reflect neuronal release, since GABA levels were increased, in a Ca2+-dependent manner, by K+-depolarization, and could be selectively decreased by an intrinsic neostriatal lesion. (5) It was not possible to clearly distinguish between the neuronal and the metabolic pools of Glu and Asp, since neostriatal Glu and Asp levels were only slightly increased by K+-depolarization, and no changes were seen after decortication. A blocker of Glu re-uptake, DHKA, had to be included in the perfusion medium in order to monitor the effect of K+-depolarization on Glu and Asp levels. Under this condition, it was found (6) that neostriatal Glu and Asp levels were significantly increased by K+-depolarization, although only increases in the Glu levels were sensitive to Ca2+ in the perfusion medium, suggesting that Glu but not Asp is released from vesicular pools. (7) Evidence is provided that selective stimulations of nigral DA cell bodies may lead to changes in release patterns from DA terminals in the ipsilateral neostriatum, which are in turn followed by discrete changes in extracellular levels of GABA and Glu in the same region. Finally, some methodological considerations are presented to clarify the contribution of neuronal release to extracellular levels of amino acid neurotransmitters in the rat neostriatum.
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  • 38
    ISSN: 1438-2199
    Keywords: Amino acids ; Asymmetric synthesis ; 2-Hydroxypinan-3-one ; Kainic acid ; Phosphonic analogue
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The enantioselective synthesis of phosphonic analogue of kainic acid is described.
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  • 39
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    Amino acids 2 (1992), S. 195-214 
    ISSN: 1438-2199
    Keywords: Amino acids ; Pulse radiolysis ; Aromatic amino acids ; Reaction mechanisms ; Free radicals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The pulse radiolysis method as well as the primary processes of water radiolysis and the spectroscopic characteristics of H, OH, HO2/O2 − and e aq - are briefly presented. Subsequently, kinetic and spectroscopic data of the transients resulting from the resolved multi site attack on aromatic amino acids are discussed. The reactivity of H and e aq - with the same substrates, as well as the effect of oxygen on the major radiolytic processes are reviewed. Finally, the formation of tryptophan radical cation is mentioned shortly. The presented radiation mechanisms are the fundamentals for radiolytic processes occurring in proteins, enzymes and hormones in the living cells.
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  • 40
    ISSN: 1438-2199
    Keywords: Amino acids ; Glutathione ; Glutathione reductase ; Glutathione S-transferase ; Chronic renal insufficiency
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Reduced glutathione (GSH) levels and glutathione reductase (GR) and glutathione S-transferase (GST) activities were investigated in the erythrocytes and lymphocytes of non-dialyzed patients with varying degrees of chronic renal insufficiency, and also of patients on regular hemodialysis treatment. GSH, GR and GST levels were higher in erythrocytes and lymphocytes of examined patients as compared to their corresponding age-matched healthy controls. A correlation was found between the degree of renal insufficiency and the above parameters tested. A routine hemodialysis did not significantly affect erythrocyte and lymphocyte GSH content and activities of its associated enzymes. The increased GSH levels as well as GSH-linked enzyme activities of blood cells in uremia may be a protective mechanism for the cells due to the accumulation of toxic, oxidizing, wastes in the blood as a result of the uremic state. This view is supported by the results ofin vitro experiments, which have shown that GR and GST activities of normal human lymphocytes are increased when incubated with plasma from uremic patients.
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  • 41
    ISSN: 1438-2199
    Keywords: Amino acids ; Glutamate ; Nucleus accumbens ; Basal ganglia ; Locomotion ; Mouse
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Following injection of 5µg of the competitive NMDA receptor antagonist AP-5 into the nucleus accumbens, but not following injection of the same dose into the dorsal striatum, a pronounced locomotor stimulation in monoamine-depleted mice was produced; theα-adrenoceptor agonist clonidine (1 mg/kg) administered ip caused a marked potentiation of an intraaccumbens AP-5 (2.5µg) injection. On the other hand, 10µg of AP-5 combined with an ip injection of clonidine (1 mg/kg) caused a marked locomotor stimulation following local application into the dorsal striatum but not following application into the prefrontal cortex. Likewise, in combination with systemically administered clonidine, a substantial locomotor stimulation was observed after application of the muscarine receptor antagonist methscopolamine (62µg) into the dorsal striatum but not into the prefrontal cortex. This study suggests that NMDA receptors in the nucleus accumbens exert an inhibitory influence on locomotor activity. The dorsal striatum may also be involved in such control via NMDA and muscarinic receptors.
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  • 42
    ISSN: 1438-2199
    Keywords: Amino acids ; Interleukin-1 ; Liver
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary We studied the effect of recombinant human IL-1β (rhIL-1β) on hepatic amino acid (AA) flux in the isolated perfused rat liver model. Two experimental groups were used — a control group (n = 5) and a rhIL-1β-treated group (n = 5). IL-1 was added to the perfusate in two successive boluses of 0.1µg and 0.9µg, respectively 35 min (final concentration 0.67 ng/ml) and 60 min (6 ng/ml) after beginning the perfusion. In the IL-1 treated group, a reduction in flux was observed for only three AA, alanine, phenylalanine and serine. Glucose and urea production in the IL-1-treated group was slightly but not-significantly lower than in the controls. rhIL-1β thus has only minor direct effects on AA flux and gluconeogenesis in the liver and cannot therefore be held responsible for the increase in hepatic amino acid uptake during stress.
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  • 43
    ISSN: 1438-2199
    Keywords: Amino acids ; Genetically Epilepsy-prone rat: GEPR ; Aspartame ; Phenylalanine ; Tyrosine ; Tryptophan ; Electroshock seizures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Seizure facilitation has been proposed as a possible adverse effect of dietary consumption of aspartame. The conversion of this sweetener to phenylalanine and aspartate in the gastrointestinal tract, and subsequent absorption, elevates plasma levels of these two amino acids. Absorbed phenylalanine competes with other large neutral amino acids, including tyrosine and tryptophan, for transport into brain. Theoretically, this competition might reduce brain tyrosine and tryptophan which could decrease synthesis of norepinephrine, dopamine and serotonin. Diminished synaptic release of these monoaminergic neurotransmitters facilitates seizures in many seizure models. Our present study evaluates effects of oral aspartame on amino acids and electroshock seizures in normal and seizure predisposed rats. Heroic doses of aspartame produced predićtable changes in plasma amino acids. However, none of the aspartame doses altered seizure indices. We conclude that aspartame does not alter maximal electroshock seizures in normal rats or in rats predisposed to seizures.
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  • 44
    ISSN: 1438-2199
    Keywords: Amino acids ; α-Amino acid esters ; Absolute configuration ; CD ; Eu(fod)3
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The NMR shift reagent, Europium(III)-tris-(1,1,1,2,2,3,3)-heptafluoro-7,7-dimethyl-4-6-octanedione [Eu(fod)3], complexes efficiently withα-amino acid esters in chloroform. These complexes exhibit characteristic circular dichroism (CD) spectral patterns in the 350-250 nm region. A fast and simple procedure (also in microscale) has been worked out which utilizes the signs of these CD bands for the determination of the absolute configuration at theα-carbon atomin situ. In the L-series, a positive CD band is observed at around 310 nm and a negative one in the 290-280 nm region. The CD spectra of the Eu complexes of the D-isomers are mirror images of those of the L-configurations. An empirical rule is proposed.
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  • 45
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    Amino acids 3 (1992), S. 213-221 
    ISSN: 1438-2199
    Keywords: Amino acids ; L-lysine oxidation ; Immobilized enzymes ; Membranes ; Leukemia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Studies have shown that specific amino acids are required for optimal growth of leukemic versus normal cells, and it is believed that the depletion of selected amino acids can abrogate tumor growth. We have developed a technique for studying the effect of amino acid deprivation on leukemic cell proliferation. The technique is based on the controlled enzymatic removal of the amino acid from leukemic blood and the subsequent measurement of cell proliferative capacity. The specific system being studied is the removal of lysine from blood using immobilized L-lysineα-oxidase. A reactor has been designed that consists of L-lysineα-oxidase and catalase co-immobilized within the void space of the porous region of asymmetric hollow fiber (ultrafiltration) membranes. Blood from leukemic sheep is currently being treatedin vitro with this reactor. By varying treatment time, the amount of enzyme immobilized, and the blood flow rate, the amount of lysine removed from the blood can be varied and controlled. Preliminary data indicate that 80% depletion of lysine from leukemic blood is enough to cause a significant (25%) decrease in total white cell count as well as a decrease in the proliferative capacity of the leukemic cells.
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  • 46
    ISSN: 1438-2199
    Keywords: Amino acids ; Prealbumin ; Nutrition ; Liver function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Prealbumin plasma level is considered a good index of liver function in liver cirrhosis. However, plasma protein levels depend not only on liver function, but also on amino acid supply which is consequent to nutritional status. In 12 cirrhotics we measured prealbumin plasma levels and the lower limb venous-artero difference of amino acid plasma levels in blood samples taken from femoral vein and femoral artery in post-absorptive conditions considered as a direct index of protein release from peripheral tissues and an indirect index of protein nutritional status. In arterial and in venous plasma amino acid sum was 1.86±0.40 (mean + sd) and 2.00 ± 0.04 mMol/l respectively. Prealbumin plasma levels were found directly correlated with the venousartero difference of amino acid plasma levels (r = 0.57p 〈 0.05) and of glutamate + glutamine levels (r = 0.73p 〈 0.007). In conclusions, these data suggest that prealbumin plasma levels are linked to amino acid supply from peripheral tissues in cirrhotics.
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  • 47
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    Amino acids 3 (1992), S. 235-241 
    ISSN: 1438-2199
    Keywords: Amino acids ; L-Tyrosine metabolism ; p-Hydroxyphenylpyruvate ; Homogentisate ; Chlortetracycline biosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary L-Tyrosine metabolism found in normal mammalian system via homogentisic acid was investigated inStreptomyces aureofaciens S-834 as L-tyrosine was shown to possess the stimulatory role in the production of chlortetracycline antibiotic. L-Tyrosine as well as the substrates of the intermediary oxidative enzymes-p-hydroxyphenylpyruvate (p-HPPA) hydroxylase and homogentisate (HGA) oxygenase were incubated with the washed, resting cells of the culture and by adding sodium diethyldithiocarbamate andα,α′-dipyridyl, the specific inhibitors of these enzymes to the culture, the oxidative intermediates-p-HPPA and HGA were blocked from further utilisation and were accumulated and isolated by extraction with the appropriate solvent system. The intermediates consisted of keto acids and aromatic phenolic acids were separated by adsorption and elution on silica gel and sephadex gel columns. p-HPPA and acetoacetate (AA) were identified as keto acids by obtaining their 2,4-dinitrophenylhydrazone derivatives. HGA as well as p-HPPA were identified as phenolic acids along with HGA lactone using diazotized reagents. These investigations helped to establish L-tyrosine oxidative pathway inStreptomyces aureofaciens via p-HPPA, HGA and AA leading to the biosynthesis of chlortetracycline antibiotic.
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  • 48
    ISSN: 1438-2199
    Keywords: Amino acids ; Tyrosine hydroxylase ; Brain ; Genetics ; Mouse
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary L-tyrosine-3-hydroxylase (TH) is the first and rate limiting enzyme in the biosynthetic pathway of catecholamine neurotransmitters (dopamine, noradrenaline, adrenaline). Implication of dopamine (DA) in various psychopathological phenomena, such as schizophrenia, has considerably contributed to the intensity of investigation of basic biochemical regulation of TH by activation and induction. Here we consider a third, constitutional (genotypic) aspect of regulation and present evidence that differences in mesencephalic (TH/SN), striatal (TH/CS), and hypothalamic (TH/HT) TH activity between virtually isogeneic strains of mice can be explained by segregating genetic factors. Biometrical genetic analysis of progenitor strains and their crosses indicated significant additive gene effects for TH/SN, TH/CS, and TH/HT, whereas dominance effects were statistically non-significant. A monogenic model of inheritance for TH/SN and TH/CS could not be rejected, while more than one gene was indicated for TH/HT. Significant positive phenotypic correlations were found in genetically segregating populations among mesencephalic, striatal and hypothalamic TH activities. This would suggest that some common genetic factors (or linked genes) are involved in the genetic variation of all three traits. A genetic selection experiment to elucidate the cellular and biochemical mechanisms underlying these variations is in progress.
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  • 49
    ISSN: 1438-2199
    Keywords: Amino acids ; Cysteine metabolism ; 3-Mercaptopyruvate pathway ; Cysteine transamination ; 3-Mercaptolactate-cysteine mixed disulfide ; Sulfate formation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary We have studied the transamination pathway (3-mercaptopyruvate pathway) ofl-cysteine metabolism in rats. Characterization of cysteine aminotransferase (EC 2.6.1.3) from liver indicated that the transamination, the first reaction of this pathway, was catalyzed by aspartate aminotransferase (EC 2.6.1.1). 3-Mercaptopyruvate, the product of the transamination, may be metabolized through two routes. The initial reactions of these routes are reduction and transsulfuration, and the final metabolites are 3-mercaptolactate-cysteine mixed disulfide [S-(2-hydroxy-2-carboxyethylthio)cysteine, HCETC] and inorganic sulfate, respectively. The study using anti-lactate dehydrogenase antiserum proved that the enzyme catalyzing the reduction of 3-mercaptopyruvate was lactate dehydrogenase (EC 1.1.1.27). Formation of HCETC was shown to depend on low 3-mercaptopyruvate sulfurtransferase (EC 2.8.1.2) activity. Results were discussed in relation to HCETC excretion in normal human subjects and patients with 3-mercaptolactate-cysteine disulfiduria. Incubation of liver mitochondria withl-cysteine, 2-oxoglutarate and glutathione resulted in the formation of sulfate and thiosulfate, indicating that thiosulfate was formed by transsulfuration of 3-mercaptopyruvate and finally metabolized to sulfate.
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  • 50
    ISSN: 1438-2199
    Keywords: Amino acids ; Cationic polypeptide ; Blood brain barrier ; Neutral amino acids transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The functionality of isolated brain microvessels — used as anin vitro model of the blood-brain barrier — can be influenced by interaction with cationic proteins. The various polylysines (Mr ranging from 0.9 to 180 kDa) tested affected the activity of both the Na+-dependent (“A”) and the Na+-independent (“L”) systems for neutral amino acid transport. Exposure to the 180 kDa polylysine caused a conspicuous inhibition of both transport systems, associated to an increased passive permeability. There was a constant, Mr-dependent, inhibition of the the L-system-mediated uptake of hydrophobic neutral amino acids. The activity of the A-system was enhanced, upon exposure to polymers larger than 22 kDa reaching its peak at 68 kDa and and declining at higher Mr values. The effect which was Na+-ions dependent and abolished by phloretine, could be essentially ascribed to an increased affinity of the MeAIB for its carrier (Km value decreasing from 265 to 169µM in presence of 68 kDa polylysine).
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  • 51
    ISSN: 1438-2199
    Keywords: Amino acids ; Polyamines ; Rat brain ; Edema ; Behavior
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary After treatment with putrescine (PUT) 200 mg/kg, i.p., male rats displayed a behavioural pattern that included wet dog shakes and motor inco-ordination. The concentration of PUT in the brain paralleled the severity of clinical signs. Histological examination showed the presence of perivascular edema and moderate spongiosis. These biochemical and histological features were present 2 h after treatment. At 24 h PUT levels in frontal cortex decreased but the histological status of brain tissue remained. Pretreatment with hyperosmolal glycerol did not modify the effect of PUT on the brain content of polyamine or the histological condition at 2 h. These results support a neurotoxic role for putrescine. Such effects were similar to those of kainic acid at convulsant doses, suggesting a role for putrescine in the action of this excitotoxin.
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  • 52
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    Amino acids 3 (1992), S. 271-286 
    ISSN: 1438-2199
    Keywords: Amino acids ; Absorption ; Mouth ; Buccal mucosa
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Certain amino acids were transported across buccal mucosa in vivo by a carrier-mediated process. Metabolic loss of L-amino acids from the mouth in a 5 min test period was negligible. The buccal mucosal transport process was stereospecific for most L-amino acids tested. The uptake of L-methionine and L-leucine showed a tendency to saturation with increasing substrate concentration. The absorption of L-leucine, L-isoleucine and L-methionine as single amino acids was inhibited in the presence of each other suggesting at least one common transport mechanism. Administration of equimolar amounts of amino acids revealed a specific pattern of absorption that could be classified into fast, intermediate, and slow groups. Absorption of some amino acids was at least partly dependent on the presence of sodium ions in the luminal solution. In conclusion, our studies demonstrate that the human buccal mucosa is permeable to L-amino acids in a selective manner, and may resemble absorption pattern similar to other locations of the gastrointestinal tract.
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  • 53
    ISSN: 1438-2199
    Keywords: Amino acids ; Elastin ; Cross-link ; Connective tissue ; Marfan's syndrome ; Aneurysm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Biochemical pathogenesis of the aortic connective tissue diseases (such as, Marfan's syndrome, dissecting aneurysm or aortic aneurysm) was examined by estimating glycoprotein, collagen and elastin contents in the aorta and the intramolecular cross-linking component (isodesmosine) and the intermolecular cross-linking components (cystine, histidinoalanine) in comparison with the control samples obtained from subjects with aortic regurgitation. The elastin content in the aorta and isodesmosine content obtained from the extract of the aortic sample found to be decreased. Ratio of cysteine residues (Cys/Cys-Cys) in the elastin fraction in disease increased. Content of histidinoalanine was found to be decreased. It may be suggested that elastin is maintained in its native nature and shape by intra- and inter-molecular cross-linking bridges, and they are readily denatured by various disease conditions. After elastin was solubilized by elastase, immunoreactive elastin content in those aortic diseases was found to be increased in the human connective tissue. Serum elastase and elastase-like activities tend to increase more than those in the control. These findings may suggest that the change in the structure of elastin would make more susceptible to elastase and other proteolytic enzymes. The reasonable hypothesis may be that molecular defect of fibillin or other constitutional structural glycoproteins produce deficient and functionally incompetent elastin associated microfibrils, and the defect of microfibrils cause to insufficient intra- and inter-molecular cross-links in elastin.
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  • 54
    ISSN: 1438-2199
    Keywords: Amino acids ; Alanyl-L-glutamine ; Glycyl-L-glutamine ; Parenteral nutrition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Utilization of intravenously administered alanyl-L-glutamine and glycyl-L-glutamine as a source of glutamine was tested in growing rats receiving total parenteral nutrition for 15 days. In experiment A the two peptides were compared to each other, in experiment B alanyl-L-glutamine was compared to an equimolar mixture of free alanine and glutamine, and in experiment C glycyl-L-glutamine was tested against an equimolar mixture of free glycine and glutamine. There was no difference of statistical significance in weight gain or nitrogen balance between the respective groups participating in the 3 experiments. Plasma levels of free glutamine were similar during infusion with alanyl-L-glutamine or glycyl-L-glutamine. The daily urinary excretion rate recorded for alanyl-L-glutamine was 3.7% and for glycyl-L-glutamine 4.3% of the infused amount. The results show that both peptides are utilized for protein synthesis and growth to approximately the same as the corresponding free amino acids.
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  • 55
    ISSN: 1438-2199
    Keywords: Amino acids ; Mitochondria ; Polyamines ; Transport ; Membrane potential
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Naturally occurring polyamines (spermidine, putrescine, cadaverine), as the well studied spermine, are transported into rat liver mitochondrial matrix provided that mitochondria are energized and the electrical membrane potential has a value of about 180 mV. This condition is achieved by the presence of inorganic phosphate, or acetate, or nigericin in the incubation medium. Valinomycin plus K+ almost completely blocks polyamine transport. The obtained results clearly show that all naturally occurring polyamines are transported by an electrophoretic mechanism in responce to a high negative inner electrical potential. The distribution ratio of polyamines across the mitochondrial membrane is far from the thermodynamic equilibrium by many orders of magnitude. This result might suggest the existence of a different pathway for polyamine efflux.
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  • 56
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    Amino acids 2 (1992), S. 77-86 
    ISSN: 1438-2199
    Keywords: Amino acids ; Fibre ; Absorption ; Liver ; Pig
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Six non-anaesthetized Large White pigs (mean body weight 59 ± 1.7 kg) were fitted with permanent catheters in the portal vein, the brachiocephalic artery and the right hepatic vein as well as with electromagnetic flow probes around the portal vein and around the hepatic artery. The animals were given a basal none-fibre diet (diet A) alone or together with 6% guar gum (diet B) or 15% purified cellulose (diet C). The diets were given for one week and according to a replicated 3 × 3 latin square design. On the last day of each such adaptation period test meals of 800 g were given prior to blood samplings. These samplings were continued for 8 h. Guar gum strongly reduced the amino acids (aa) and urea absorption as well as the hepatic production of urea. The aa profile of the absorbed mixture was not strongly modified by guar gum ingestion as well as the profile of the hepatic aa uptake. Cellulose at the consumed level had very few effects on the considered parameters. It is suggested that the modulation of intestinal mechanisms by guar gum was sufficient to mediate the latter internal metabolic effects.
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  • 57
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    Amino acids 2 (1992), S. 97-102 
    ISSN: 1438-2199
    Keywords: Amino acids ; Helicoidal polymer phase ; Amino acid molecule ; Chirality ; Chiral revealer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The interaction between a helix and an amino acid molecule is determined on the basis of semi-empirical potentials including Lennard-Jones, electrostatic, induction and hydrogen bond contributions. Calculations are performed for various values of the helix characteristics which schematize helicoidal polysaccharides (cellulose, cellulose derivatives⋯). The helix configuration acts as a chiral revealer as it frozes the amino acid inside its cavity. The chiral discriminatory ratio is maximum for similar sizes of the cavity and of the analyte.
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  • 58
    ISSN: 1438-2199
    Keywords: Amino acids ; Capillary zone electrophresis ; Micellar electrokinetic chromatography ; OPA-derivatives ; Enantiomer determination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Amino acids react with OPA and chiral mercaptans to give diastereomeric isoindole derivatives. The resolution of these diastereomers was investigated by micellar electrokinetic chromatography (MECC) and free solution capillary electrophoresis. MECC with SDS as micellar phase allows to separate the amino acid derivatives and to resolve the diastereomers. The separation is influenced by the amount of detergent and the organic modifier added. Capillary zone electrophoresis offers a valuable alternative to the traditional methods for amino acid analysis and enantiomer determination.
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  • 59
    ISSN: 1438-2199
    Keywords: Amino acids ; Porcine pancreatic lipase ; Asymetric resolution of amino acids ; PPL-enantioselective methyl ester hydrolysis ; PPL-resolution of amino acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A preparative-scale enantioselective hydrolysis of racemic methyl esters of several N-protected amino acid has been carried out by using crude porcine pancreatic lipase (Triacylglycerol lipase, EC 3.1.1.3) PPL as a hydrolytic enzyme. In all cases 50% of the racemic methyl ester was hydrolysed to the N-protected L-amino acid with high yield and high optical purity. Hydrolysis rates were very close related not only to the amino acid structure but also to the steric and/or electronic nature of the ester and N-protecting groups. Thus, the very convenient ester methyl group can be enantioselectively hydrolysed with PPL when N-protecting group is a carbonyl derivative, as it is the usual benzoyl group.
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  • 60
    ISSN: 1438-2199
    Keywords: Amino acids ; Schizophrenia ; Neuroleptic drug response ; Serum amino acids ; Central monoamines
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Altered dopamine turnover has been postulated as underlying cause for schizophrenia. This is partially inferred from pharmacological studies and from changes in serum dopamine and dopamine metabolite levels. It is not clear whether the serum amino acid precursors' availability and neurotransmitter-mediated hormonal release could be indicative of the neurotransmitter turnover. We speculate in this context that the profile of serum amino acids and neurotransmitters reflects differences of neurotransmitter activity in the central nervous system and may be considered in a broad sense “window to the brain”. We analyzed basal serum amino acids (including monoamine precursors), and monoamines in schizophrenic patients after a drug holiday of 3 or more days, and in healthy subjects. Asparagine, phenylalanine, and cystine were higher and tyrosine, tryptophan, and the ratio of tryptophan to competing amino acids lower in schizophrenic patients than in healthy subjects (P 〈 0.05). Dopamine was increased in schizophrenic patients compared to healthy subjects. We speculate that these results sustain the notion for dopamine overactivity in schizophrenia, which might be caused by altered amino acid precursor availability.
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  • 61