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  • Articles  (178)
  • Nitrogen fixation  (100)
  • Regulation  (84)
  • 1
    ISSN: 1432-072X
    Keywords: Alanine dehydrogenase ; Anabaena cylindrica ; Heterocysts ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The l-alanine dehydrogenase (ADH) of Anabaena cylindrica has been purified 700-fold. It has a molecular weight of approximately 270000, has 6 sub-units, each of molecular weight approximately 43000, and shows activity both in the aminating and deaminating directions. The enzyme is NADH/NAD+ specific and oxaloacetate can partially substitute for pyruvate. The K m app for NAD+ is 14 μM and 60 μM at low and high NAD+ concentrations, respectively. The K m app for l-alanine is 0.4 mM, that for pyruvate is 0.11 mM, and that for oxaloacetate is 3.0 mM. The K m app for NH 4 + varies from 8–133 mM depending on the pH, being lowest at high pH levels (pH 8.7 or above). Alanine, serine and glycine inhibit ADH activity in the aminating direction. The enzyme is active both in heterocysts and vegetative cells and activity is higher in nitrogen-starved cultures than in N2-fixing cultures. The data suggest that although alanine is formed by the aminating activity of ADH, entry of newly fixed ammonia into organic combination does not occur primarily via ADH in N2-fixing cultures of A. cylindrica. Ammonia assimilation via ADH may be important in cultures with an excess of available nitrogen. The deaminating activity of the enzyme may be important under conditions of nitrogen-deficiency.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Archives of microbiology 110 (1976), S. 207-213 
    ISSN: 1432-072X
    Keywords: Nitrogen fixation ; NH 4 + excretion ; Photosynthesis ; Rhodospirillum rubrum ; Photosynthetic bacteria ; Enzymes of ammonia assimilation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract NH 4 + excretion was undetectable in N2-fixing cultures ofRhodospirillum rubrum (S-1) and nitrogenase activity in these cultures was repressed by the addition of 10 mM NH 4 + to the medium. The glutamate analog,l-methionine-dl-sulfoximine (MSX), derepressed N2 fixation even in the presence of 10 mM extracellular NH 4 + . When 10 mg MSX/ml was added to cultures just prior to nitrogenase induction they developed nitrogenase activity (20% of the control activities) and excreted most of their fixed N2 as NH 4 + . Nitrogenase activities and NH 4 + production from fixed N2 were increased considerably when a combined nitrogen source, NH 4 + (〉40 μmoles NH 4 + /mg cell protein in 6 days) orl-glutamate (〉60 μmoles NH 4 + /mg cell protein in 6 days) was added to the cultures together with MSX. Biochemical analysis revealed thatR. rubrum produced glutamine synthetase and glutamate synthase (NADP-dependent) but no detectable NADP-dependent glutamate dehydrogenase. The specific activity of glutamine synthetase was observed to be maximal when nitrogenase activity was also maximal. Nitrogenase and glutamine synthetase activities were repressed by NH 4 + as well as by glutamate. The results demonstrate that utilization of solar energy to photoproduce large quantities of NH 4 + from N2 is possible with photosynthetic bacteria by interfering with their regulatory control of N2 fixation.
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  • 3
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    Electronic Resource
    Springer
    Archives of microbiology 112 (1977), S. 283-285 
    ISSN: 1432-072X
    Keywords: Wine yeasts ; Sulfur metabolism ; Regulation ; Sulfate uptake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Five different strains of wine yeasts were investigated with respect to active uptake of [35S] sulfate and its regulation by methionine. Considerable differences exist between “low” and “high” sulfite-producing strains in the initial velocity of sulfate uptake. Further differences were established in repression of sulfate permease by l-methionine, most evident in a total lack of repression in one of the “high” sulfite producers. These findings explain in part variable sulfite and sulfide formation.
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  • 4
    ISSN: 1432-072X
    Keywords: cAMP ; Regulation ; Chlorophyll synthesis ; Chlorella fusca
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The intracellular concentration of cAMP in the green alga Chlorella fusca was in the range of 2 · 10-9 to 10-8 moles/g dry weight and was strongly dependent on the growth conditions. The cAMP level was high with high light intensity, low nitrate or glucose concentration. Intracellular cAMP increased only by factor of 2 when high amounts (up to 10-3 M) of cAMP were added to the medium. Most of the given cAMP was converted to 5′-AMP. Addition of cAMP had little effect on the chlorophyll content of the cells, only at 10-6 M some enhancement in photoautotrophic cultures was observed. On the other hand high amounts of cAMP in the medium increased the growth rate. DBcAMP* showed a positive effect on chlorophyll synthesis and growth rate at much lower concentrations compared to cAMP. Stimulation effects of exogenous cAMP on the synthesis of chlorophyll were also observed in mixotrophic cultures with a high glucose/nitrate ratio, conditions where chlorophyll synthesis is repressed. Similar to autotrophic conditions DBcAMP was more effective than cAMP. These data indicate that cAMP may act in a system controlling the chlorophyll content of the cells in response to nutrients or light.
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  • 5
    ISSN: 1432-072X
    Keywords: Root nodule symbiosis ; Rhizobium meliloti ; Medicago sativa ; Nitrogenase activity ; Regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Symbiotic nitrogen fixation of Rhizobium meliloti bacteroids in Medicago sativa root nodules was suppressed by several inorganic nitrogen sources. Amino acids like glutamine, glutamic acid and aspartic acid, which can serve as sole nitrogen sources for the unnodulated plant did not influence nitrogenase activity of effective nodules, even at high concentrations. Ammonia and nitrate suppressed symbiotic nitrogen fixation in vivo only at concentrations much higher than those needed for suppression of nitrogenase activity in free living nitrogen fixing bacteria. The kinetics of suppression were slow compared with that of free living nitrogen fixing bacteria. On the other hand, nitrite, which acts as a direct inhibitor of nitrogenase, suppressed very quickly and at low concentrations. Glutamic acid and glutamine enhanced the effect of ammonia dramatically, while the suppression by nitrate was enhanced only slightly.
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  • 6
    ISSN: 1432-072X
    Keywords: Physarum polycephalum ; Amoebae ; Aminopeptidases ; Acid proteases ; Regulation ; Development ; Differential gene activity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The cultivation of Physarum polycephalum amoebae in two media with different protein contents revealed a regulation of aminopeptidases and proteases depending on the albumin content of the medium: in growing amoebae and plasmodia the aminopeptidases have similar isoenzyme patterns and relative activities against nitroanilides. One alanine and four leucine aminopeptidase isoenzymes were found within the slightly acid pH range. During growth amoebae secrete—different from plasmodia—leucine aminopeptidase into the medium with low protein content. In an albumin-rich medium additional alanine aminopeptidase activity was found. Out of nine plasmodial proteases four were found in amoebae too. Only one band (pI 3.6) was present in the protein-poor medium. No protease activity could be detected in the proteinrich medium.
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  • 7
    ISSN: 1432-072X
    Keywords: Cyanobacteria ; Knallgas reaction ; Hydrogenase ; Hydrogen utilization ; Nitrogenase ; Nitrogen fixation ; Isolated heterocysts ; Anabaena cylindrica ; Nostoc muscorum ; Anabaena variabilis ; Anacystis nidulans ; Cyanophora paradoxa
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Several blue-green algae were surveyed for the occurrence of the hydrogenase which was assayed by the oxyhydrogen or Knallgas reaction in the intact organisms. In aerobically grown cultures, the reaction was detectable in Anabaena cylindrica, Nostoc muscorum and in two Anabaena variabilis species, whereas virtually no activity was observed in Anacystis nidulans and Cyanophora paradoxa. In these latter two algae, the reaction was, however, found after growth under molecular hydrogen for several days, which drastically increased the activity levels with all the algae tested. In the nitrogen fixing species, the activity of the Knallgas reaction was enhanced when all combined nitrogen was omitted from the media. H2 and hydrogenase could not significantly support the CO2-fixation in photoreduction experiments with all blue-green algae investigated here. Hydrogenase was assayed by the dithionite and methyl viologen dependent evolution of hydrogen and was found to be present with essentially the same specific activity levels in preparations of both heterocysts and vegetative cells from Anabaena cylindrica. Na2S2O4 as well as H2 supported the C2H2-reduction of the isolated heterocysts. The H2-dependent C2H2-reduction did not require the presence of oxygen but was strictly light-dependent where H2 served as an electron donor to photosystem I of these cells. It is concluded that hydrogen can be utilized by two different pathways in blue-green algae.
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  • 8
    ISSN: 1432-072X
    Keywords: Streptococcus cremoris ; Cell wall proteinase ; Calcium dependency ; Regulation ; Translational control
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The persistent accumulation of proteinase (PIII) activity in the cell wall of Streptococcus cremoris strain AM1 during growth depends on the presence of Ca2+-ions in the medium. In the absence of calcium initial accumulation of activity in the cell wall is observed, followed by a decrease to a low final level. Under this condition no increase of proteolytic activity is found in the extracellular fluid. A possible function of calcium in the stabilization of the enzyme is discussed. Prolonged accumulation of catalytically active proteinase PIII in the cell wall occurs in the absence of messenger ribonucleic acid synthesis. This process involves de novo protein synthesis supported by preformed proteinase-specific messenger ribonucleic acid, which is possibly either intrinsically long-lived or is stabilized following its transcription. The level of the extracellular concentration of amino acids and/or peptides regulates the translation of newly synthesized proteinase-specific messenger ribonucleic acid and, possibly, the growth of the organism in milk.
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  • 9
    ISSN: 1432-072X
    Keywords: Blue-green algae ; Nitrogen fixation ; Anabaena ; Cyanobacteria ; Marine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Five strains of heterocystous blue-green algae capable of high rates of growth and nitrogenase activity were isolated from shallow coastal environments. Growth of the organisms was characterized with respect to temperature, NaCl concentration in the medium, and nitrogen source. The temperature optima ranged from 35–42°C, and all but one of the strains displayed a requirement for added NaCl. The generation times under N2-fixing conditions were 5.1–5.9 h, and were as low as 3.4 h for growth on NH4Cl. Nitrogenase activity (C2H2 reduction) was high throughout the logarithmic growth phase of each strain. The maximum value observed for one strain was 65.5 nmoles C2H4 produced/mg protein x min, and the average values for the five strains ranged from 24.5–46.7 nmoles C2H4/mg protein x min. The organisms all belong to the genusAnabaena. The growth and nitrogenase activity of these strains are much higher than those of the heterocystous blue-green algae commonly used for investigation of nitrogen metabolism, and they thus should prove to be useful physiological tools. Their prevalence, as judged by the ease of their enrichment and isolation, in bay and estuarine environments suggests that they are important contributors of combined nitrogen.
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  • 10
    ISSN: 1432-072X
    Keywords: Rhizobium japonicum ; Nitrogenase activity ; Nitrogen fixation ; Organic acids ; Cell-morphology ; Bacteroids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Rhizobium japonicum 61-A-101 grew and fixed nitrogen more effectively on media containing an organic acid and a pentose sugar than on media containing only one of these carbon sources. Peak specific activities in the range 10–15 nmol C2H4 · h-1 · mg protein-1 were found for these organisms in a spot of growth about 1 cm diameter on agar surfaces exposed to air. Increasing concentrations of the organic acids (succinate or malonate) in a medium containing arabinose resulted in longer lasting activity. The inclusion of a third carbon source, glycerol, gave activity which remained at the maximum from about the 8 to the 18 day after inoculation although no growth of the bacteria occurs during the last 8 or 10 days. At low concentration of organic acid l-arabinose was a much better carbon source for supporting nitrogenase activity of these organisms that the d-form. Both organic acids affected the morphology of the bacteria. Higher concentrations, especially of malonate, gave swollen and distorted cells. When bacteria growing on organic acid-containing agar plates were suspended and plated after appropriate dilution on yeast extract — mannitolglycerol agar there was heterogeneity of colony form, with up to 90% microcolonies after growth on high malonate concentrations. The effects of malonate may be correlated with characteristics of the bacteroid form inside the nodule which contains relatively high concentrations of organic acids, especially malonate.
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