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  • Springer  (15)
  • 1
    ISSN: 1432-1130
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Nicotinamide (NA) yields a polarographic catalytic wave with a peak potential –1.38 V (vs. SCE) in 0.1 mol/L HAc-NaAc (pH 4.7)/4 × 10–3 mol/L KIO3 buffer solution. The sensitivity of the catalytic wave increased in one order of magnitude as compared to that of the responding reduction wave without KIO3. Based on this observation, a new method for the determination of NA was recommended. The second order derivative peak current was proportional to the NA concentration in the range of 5 × 10–8 – 6 × 10–7 mol/L. 0.11-fold vitamin B1, 0.13-fold B2, 0.14-fold B6 and 8-fold nicotinic acid amounts do not interfere the determination of 1 × 10–6 mol/L NA. The proposed method was used to determine the NA content in multivitamin tablets, with good agreement to the declared amount.
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  • 2
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Annual and seasonal variations in the low-latitude topside ionosphere are investigated using observations made by the Hinotori satellite and the Sheffield University Plasmasphere Ionosphere Model (SUPIM). The observed electron densities at 600 km altitude show a strong annual anomaly at all longitudes. The average electron densities of conjugate latitudes within the latitude range ±25° are higher at the December solstice than at the June solstice by about 100% during daytime and 30% during night-time. Model calculations show that the annual variations in the neutral gas densities play important roles. The model values obtained from calculations with inputs for the neutral densities obtained from MSIS86 reproduce the general behaviour of the observed annual anomaly. However, the differences in the modelled electron densities at the two solstices are only about 30% of that seen in the observed values. The model calculations suggest that while the differences between the solstice values of neutral wind, resulting from the coupling of the neutral gas and plasma, may also make a significant contribution to the daytime annual anomaly, the E × B drift velocity may slightly weaken the annual anomaly during daytime and strengthen the anomaly during the post-sunset period. It is suggested that energy sources, other than those arising from the 6% difference in the solar EUV fluxes at the two solstices due to the change in the Sun-Earth distance, may contribute to the annual anomaly. Observations show strong seasonal variations at the solstices, with the electron density at 600 km altitude being higher in the summer hemisphere than in the winter hemisphere, contrary to the behaviour in NmF2. Model calculations confirm that the seasonal behaviour results from effects caused by transequatorial component of the neutral wind in the direction summer hemisphere to winter hemisphere.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Annales geophysicae 18 (2000), S. 789-798 
    ISSN: 0992-7689
    Keywords: Ionosphere (equatorial ionosphere; ionosphere-atmosphere interactions; plasma temperature and density)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Observations made by the Hinotori satellite have been analysed to determine the yearly variations of the electron density and electron temperature in the low-latitude topside ionosphere. The observations reveal the existence of an equinoctial asymmetry in the topside electron density at low latitudes, i.e. the density is higher at one equinox than at the other. The asymmetry is hemisphere-dependent with the higher electron density occurring at the March equinox in the Northern Hemisphere and at the September equinox in the Southern Hemisphere. The asymmetry becomes stronger with increasing latitude in both hemispheres. The behaviour of the asymmetry has no significant longitudinal and magnetic activity variations. A mechanism for the equinoctial asymmetry has been investigated using CTIP (coupled thermosphere ionosphere plasmasphere model). The model results reproduce the observed equinoctial asymmetry and suggest that the asymmetry is caused by the north-south imbalance of the thermosphere and ionosphere at the equinoxes due to the slow response of the thermosphere arising from the effects of the global thermospheric circulation. The observations also show that the relationship between the electron density and electron temperature is different for daytime and nighttime. During daytime the yearly variation of the electron temperature has negative correlation with the electron density, except at magnetic latitudes lower than 10°. At night, the correlation is positive.
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  • 4
    ISSN: 1432-069X
    Keywords: Phorbol 12-myristate ; 13-acetate ; Melanocyte ; Cell differentiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Pure human melanocyte cultures were established in a serum-free medium containing epidermal growth factor (10 ng/ml), hydrocortisone (10−7 M), insulin (5 Μg/ ml), transferrin (10 Μg/ml), cholera toxin (2 ng/ml), isobutylmethyl xanthine (10−4 M) and bovine pituitary extract (30 Μg/ml). To investigate the biological effects of PMA on melanocytes in vitro, the cells were incubated in media containing various concentration of PMA (including 0 nM, 85 nM and 170 nM), and grown continuously for 12 days without passage. The cells were observed for changes in cell morphology, cell cycle, cytoskeleton and HLA-DR expression. In addition, the effect of PMA on tyrosinase activity was also evaluated. The results revealed that the higher the PMA concentration, the higher the percentage of large irregularly shaped melanocytes. These large melanocytes were three to ten times the size of small bipolar or multipolar cells. A higher concentration of PMA was also associated with a higher percentage of melanocytes in the S and G2-M phases of the cell cycle and with a higher percentage of melanocytes as tetraploid and octaploid karyotypes. The cytoskeleton (vimentin) in the large irregularly shaped cells appeared disaggregated as compared with that in the usual dendritic cells with a compact distribution. HLA-DR was found to be expressed on some melanocytes growing in media containing PMA, appearing both in large dendritic cells and large irregularly shaped cells. None of the cells expressed HLA-DR when cultured in the abscence of PMA. PMA at 85 nM, but not at 170 nM, significantly stimulated tyrosinase activity as compared with the controls (0 nM PMA). It thus seems appropriate to study the carcinogenic or other properties of melanocytes in systems that do not contain PMA, such as the serum-free medium proposed by us.
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  • 5
    ISSN: 1573-7217
    Keywords: sphingolipid metabolites ; sphingosine-1-phosphate ; PDGF ; invasiveness ; human breast cancer cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary This review will focus on the role of sphingosine and its phosphorylated derivative sphingosine-1-phosphate (SPP) in cell growth regulation and signal transduction. We will show that many of the effects attributed to sphingosine in quiescent Swiss 3T3 fibroblasts are mediated via its conversion to SPP. We propose that SPP has appropriate properties to function as an intracellular second messenger based on the following: it elicits diverse cellular responses; it is rapidly produced from sphingosine by a specific kinase and rapidly degraded by a specific lyase; its concentration is low in quiescent cells but increases rapidly and transiently in response to the growth factors, fetal calf serum (FCS) and platelet derived growth factor (PDGF); it releases Ca2+ from internal sources in an InsP3-independent manner; and finally, it may link sphingolipid signaling pathways to cellularras-mediated signaling pathways by elevating phosphatidic acid levels. The effects of this novel second messenger on growth, differentiation and invasion of human breast cancer cells will be discussed.
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  • 6
    ISSN: 1573-4919
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary The localization of γ-aminobutyric acid (GABA) neurons in the goldfish and the rabbit retina has been studied by immunocytochemical localization of the GABA-synthesizing enzyme L-glutamate decarboxylase (GAD, L-glutamate 1-carboxy-lase, EC 4.1.1.15) and by [3H] GABA uptake autoradiography. In the goldfish retina, GAD is localized in some horizontal cells (H1 type), a few amacrine cells and sublamina b of the inner plexiform layer. Results from immunocytochemical studies of GAD-containing neurons and autoradiographic studies of GABA uptake reveals a marked similarity in the labeling pattern suggesting that in goldfish retina, the neurons which possess a high-affinity system for GABA uptake also contain significant levels of GAD. In the rabbit retina, when Triton X-100 was included in immunocytochemical incubations with a modified protein A-peroxidase-antiperoxidase method, reaction product was found in four broad, evenly spaced laminae within the inner plexiform layer. In the absence of the detergent, these laminae were seen to be composed of small, punctate deposits. When colchicine was injected intravitreally before glutamate decarboxylase staining, cell bodies with the characteristic shape and location of amacrine cells were found to be immunochemically labeled. Electron microscopic examination showed that these processes were presynaptic to ganglion cell dendrites (infrequently), amacrine cell telodendrons, and bipolar cell terminals. Often, bipolar cell terminals were found which were densely innervated by several GAD-positive processes. No definite synapses were observed in which a GAD-positive process represented the postsynaptic element. In autoradiographic studies by intravitreal injection of [3H] GABA a diffuse labeling of the inner plexiform layer and a dense labeling of certain amacrine cell bodies in the inner nuclear layer was observed. Both immunocytochemical and autoradiographic results support the notion that certain, if not all, amacrine cells use GABA as their neurotransmitter.
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  • 7
    ISSN: 1573-4919
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary The localization of γ-aminobutyric acid (GABA) neurons in the goldfish and the rabbit retina has been studied by immunocytochemical localization of the GABA-synthesizing enzyme L-glutamate decarboxylase (GAD, L-glutamate 1-carboxy-lase, EC 4.1.1.15) and by [3H] GABA uptake autoradiography. In the goldfish retina, GAD is localized in some horizontal cells (H1 type), a few amacrine cells and sublamina b of the inner plexiform layer. Results from immunocytochemical studies of GAD-containing neurons and autoradiographic studies of GABA uptake reveals a marked similarity in the labeling pattern suggesting that in goldfish retina, the neurons which possess a high-affinity system for GABA uptake also contain significant levels of GAD. In the rabbit retina, when Triton X-100 was included in immunocytochemical incubations with a modified protein A-peroxidase-antiperoxidase method, reaction product was found in four broad, evenly spaced laminae within the inner plexiform layer. In the absence of the detergent, these laminae were seen to be composed of small, punctate deposits. When colchicine was injected intravitreally before glutamate decarboxylase staining, cell bodies with the characteristic shape and location of amacrine cells were found to be immunochemically labeled. Electron microscopic examination showed that these processes were presynaptic to ganglion cell dendrites (infrequently), amacrine cell telodendrons, and bipolar cell terminals. Often, bipolar cell terminals were found which were densely innervated by several GAD-positive processes. No definite synapses were observed in which a GAD-positive process represented the postsynaptic element. In autoradiographic studies by intravitreal injection of [3H] GABA a diffuse labeling of the inner plexiform layer and a dense labeling of certain amacrine cell bodies in the inner nuclear layer was observed. Both immunocytochemical and autoradiographic results support the notion that certain, if not all, amacrine cells use GABA as their neurotransmitter.
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  • 8
    ISSN: 1573-0875
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
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  • 9
    ISSN: 1476-5535
    Keywords: Keywords: sucrose; isomaltulose; trehalulose; isomaltulose synthase; Klebsiella planticola
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An isomaltulose-producing bacterium was isolated and taxonomically characterized. Its morphological and biochemical properties conform best to those described for Klebsiella planticola. When cultured under optimal conditions, the organism simultaneously converted sucrose into both isomaltulose (α-D-glucopyranosyl-1,6-fructose) and trehalulose (α-D-glucopyranosyl-1,1-fructose) with substrate conversion rates of 80% and 15%, respectively. Sucrose and Bacto-tryptone were the most effective carbon and supplemental nitrogen sources, respectively, for producing cells of high isomaltulose-forming ability. None of several inorganic salts tested had any significant effect. The major product formed in the reaction mixture was verified to be isomaltulose by co-chromatography and IR spectroscopy.
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  • 10
    ISSN: 1476-5535
    Keywords: chitin ; chitinase ; Aeromonas sp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract A bacterial strain secreting potent chitinolytic activity was isolated from shrimp-pond water by enrichment culture using colloidal crab-shell chitin as the major carbon source. The isolated bacterium, designated asAeromonas sp No. 16 exhibited a rod-like morphology with a polar flagellum. Under optimal culture conditions in 500-ml shaker flasks, it produced a chitinolytic activity of 1.4 U ml−1. A slightly higher enzymatic activity of 1.5 U ml−1 was obtained when cultivation was carried out in a 5-liter jar fermentor using a medium containing crystalline chitin as the carbon source. The secretion of the enzyme(s) was stimulated by several organic nitrogenous supplements. Most carbon sources tested (glucose, maltose, N-acetylglucosamine, etc) enhanced cell growth, but they slightly inhibited enzyme secretion. Glucosamine (0.5% w/v) severely inhibited cell growth (16% of the control), but it did not significantly affect enzyme secretion. The production of chitinolytic enzymes was pH sensitive and was enhanced by increasing the concentration of colloidal chitin to 1.5%. The observed chitinolytic activity could be attributed to the presence of β-N-acetylglucosaminidase and chitinase. Chitinase was purified by ammonium sulfate fractionation and preparative gel electrophoresis to three major bands on SDS-PAGE. An in-gel enzymatic activity assay indicated that all three bands possessed chitinase activity. Analysis of the enzymatic products indicated that the purified enzyme(s) hydrolyzed colloidal chitin predominantly to N,N-diacetyl-chitobiose and, to a much lesser extent, the mono-, tri, and tetramer of N-acetylglucosamine, suggesting that they are mainly endochitinases.
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