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Query: EC:1.4.1.2 (glutamate dehydrogenase)
 4,380 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Two pathways of ammonium assimilation are known in bacteria, one mediated by glutamate dehydrogenase, the other by glutamine synthetase and glutamate synthase. The activities of these three enzymes were measured in crude extracts from four Rhizobium meliloti wild-type strains, 2011, M15S, 444 and 12. All the strains had active glutamine synthetase and NADP-linked glutamate synthase. Assimilatory glutamate dehydrogenase activity was present in strains 2011, M15S, 444, but not in strain 12. Three glutamate synthase deficient mutants were isolated from strain 2011. They were unable to use 1 mM ammonium as a sole nitrogen source. However, increased ammonium concentration allowed these mutants to assimilate ammonium via glutamate dehydrogenase. It was found that the sole mode of ammonium assimilation in strain 12 is the glutamine synthetase-glutamate synthase route; whereas the two pathways are functional in strain 2011.
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PMID:The pathways of ammonium assimilation in Rhizobium meliloti. 611 83

In Neurospora crassa the assimilation of high and low concentrations of ammonium occurs by two different pathways. When the fungi are growing exponentially on ammonium excess, this compound is fixed by a glutamic dehydrogenase and an octameric glutamine synthetase (GS). The synthesis of this GS polypeptide (beta) is regulated by the nitrogen source present in excess; being higher on glutamate, intermediate on ammonium, and lower on glutamine. When N. crassa is growing in fed-batch ammonium-limited cultures a different polypeptide of GS (alpha), arranged as a tetramer, is synthesized. In both conditions synthesis in vivo correlates with the data obtained with an in vitro translation system primed with N. crassa RNA. This different expression of alpha and beta GS polypeptides was also observed when the cultures were shifted from excess to low nitrogen, and vice versa. By agarose gel electrophoresis in the presence of methylmercury hydroxide, some separation of different mRNAs that direct the in vitro synthesis of alpha and beta GS polypeptides has been accomplished. Data are presented that establish the operation of the tetrameric alpha GS and of glutamate synthase in the assimilation of ammonium in low concentration.
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PMID:Physiology of ammonium assimilation in Neurospora crassa. 612 Sep 27

The relationship between chloramphenicol production and nitrogen metabolism in Streptomyces venezuelae was examined in stirred jar cultures under pH control. Nitrogen sources that supported rapid biomass accumulation gave low rates of antibiotic synthesis during growth. This was consistent with a general incompatibility between fast growth and high yields of chloramphenicol. In media where the growth rate was reduced below the attainable maximum by the rate at which nitrogen could be assimilated, chloramphenicol production was associated with biomass accumulation. Enzymes that are potentially associated with nitrogen assimilation pathways were assayed in cultures supplied with nitrogen sources supporting markedly different growth rates. The results indicated that glutamine synthetase and alanine dehydrogenase levels were relatively insensitive to changes in growth rate and nitrogen source depletion. Glutamate dehydrogenase and glutamate synthase, on the other hand, showed high activity in cultures assimilating ammonium nitrogen and markedly decreased activity with poorer nitrogen sources or when ammonium was depleted. If chloramphenicol biosynthesis is coordinately controlled by mechanisms that regulate nitrogen assimilation, glutamate synthase and glutamate dehydrogenase are the most likely enzymes that manifest the regulatory linkage.
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PMID:Nitrogen metabolism and chloramphenicol production in Streptomyces venezuelae. 614 5

Glutamate synthase catalyzes glutamate formation from 2-oxoglutarate plus glutamine and plays an essential role when glutamate biosynthesis by glutamate dehydrogenase is not possible. Glutamate synthase activity has been determined in a number of Neurospora crassa mutant strains with various defects in nitrogen metabolism. Of particular interest were two mutants phenotypically mute except in an am (biosynthetic nicotinamide adenine dinucleotide phosphate-glutamate dehydrogenase deficient, glutamate requiring) background. These mutants, i and en-am, are so-called enhancers of am; they have been redesignated herein as en(am)-1 and en(am)-2, respectively. Although glutamate synthase levels in en(am)-1 were essentially wild type, the en(am)-2 strain was devoid of glutamate synthase activity under all conditions examined, suggesting that en(am)-2 may be the structural locus for glutamate synthase. Regulation of glutamate synthase occurred to some extent, presumably in response to glutamate requirements. Glutamate starvation, as in am mutants, led to enhanced activity. In contrast, glutamine limitation, as in gln-1 mutants, depressed glutamate synthase levels.
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PMID:Glutamate synthase levels in Neurospora crassa mutants altered with respect to nitrogen metabolism. 615 51

The influence of the relA1 mutation on the regulation of the ammonia assimilatory enzymes, glutamate dehydrogenase (EC 1.4.1.4), glutamine synthetase (EC 6.3.1.2), and glutamate synthase (EC 1.4.1.3), was examined. When cells grown in rich media (either Luria broth or glucose-ammonia plus casamino acids) were transferred to a glucose-ammonia medium, the relA mutant failed to resume growth and did not have the same increase in any of the assimilatory enzyme activities as the rel+ strain. This effect was particularly dramatic for glutamate dehydrogenase, which increased 6-fold in the rel+ strain. Measurements of the guanosine nucleotide concentrations showed that the rel+ strain had a ppGpp concentration about 9 times that of the relA mutant 5 min after the shift to minimal medium. These results are consistent with those for other biosynthetic enzymes and show that the ammonia assimilatory enzymes require a relA product for their synthesis during shift from rich to minimal media. In addition, we examined the response of these strains to a change in nitrogen source. The relA mutant again failed to resume growth after a shift from glucose-ammonia to glucose-arginine medium. Even though the ppGpp concentration did not increase, the rel+ strain grew and increased glutamine synthetase activities about 2-fold. These changes the absence of increased ppGpp levels suggest that some other relA-mediated function is important during this change in nitrogen source.
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PMID:The regulation of the ammonia assimilatory enzymes in Rel+ and Rel- strains of Salmonella typhimurium. 628 74

Glutamic acid is synthesized in enteric bacteria by either glutamate dehydrogenase or by the coupled activities of glutamate synthase and glutamine synthetase. A hybrid plasmid containing a fragment of the Salmonella typhimurium chromosome cloned into pBR328 restores growth of glutamate auxotrophs of S. typhimurium and Escherichia coli strains which have mutations in the genes for glutamate dehydrogenase and glutamate synthase. A 2.2-kilobase pair region was shown by complementation analysis, enzyme activity measurements, and the maxicell protein synthesizing system to carry the entire glutamate dehydrogenase structural gene, gdhA. Glutamate dehydrogenase encoded by gdhA carried on recombinant plasmids was elevated 5- to over 100-fold in S. typhimurium or E. coli cells and was regulated in both organisms. The gdhA promoter was located by recombination studies and by the in vitro fusion to, and activation of, a promoter-deficient galK gene. Additionally, S. typhimurium gdhA DNA was shown to hybridize to single restriction fragments of chromosomes from other enteric bacteria and from Saccharomyces cerevisiae.
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PMID:Cloning and characterization of gdhA, the structural gene for glutamate dehydrogenase of Salmonella typhimurium. 636 Sep 94

NH+4 produced as a result of the activation of AMP deaminase (AMP aminohydrolase, EC 3.5.4.6) was utilized effectively to form glutamate from 2-oxoglutarate by the action of NADP-glutamate dehydrogenase (L-glutamate:NADP+ oxidoreductase (deaminating), EC 1.4.1.4) under in situ conditions in yeast cells: the decrease in total adenylates stoichiometrically corresponded to the production of NH+4 plus glutamate. Reducing equivalents, NADPH, for the synthesis of glutamate can be supplied by the pentose phosphate pathway. The addition of spermine, an activator of AMP deaminase without changes in glutamate dehydrogenase activity, resulted in an increase in ammonium concentration, which can enhance the formation of glutamate from 2-oxoglutarate. A close correlation of NADP-glutamate dehydrogenase with AMP deaminase activity was observed under various growth conditions. The interaction of the AMP deaminase-ammonium system with glutamate dehydrogenase as an ammonium-assimilating reaction may participate in the control of the cellular NH+4 level, which can correlate with glycolysis.
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PMID:Interaction of the AMP deaminase-ammonium system with glutamate dehydrogenase in yeast. 675 3

The glutamate dehydrogenase gene of Escherichia coli has been cloned into broad host-range plasmids and can complement glutamate synthase mutants of Methylophilus methylotrophus. Assimilation of ammonia via glutamate dehydrogenase is more energy-efficient than via glutamate synthase, thus the recombinant organism converts more growth substrate, methanol, into cellular carbon.
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PMID:Improved conversion of methanol to single-cell protein by Methylophilus methylotrophus. 677 10

The relationship between oxidized nicotinamide adenine dinucleotide (phosphate) [NAD(P)+] transhydrogenase (EC 1.6.1.1) and NAD(P)+ glutamate dehydrogenase in several enteric bacteria which differ slightly in their regulation of nitrogen metabolism was studied. Escherichia coli strain K-12 was grown on glucose and various concentrations of NH4Cl as the sole nitrogen source. In the range of 0.5 to 20 mM NH4Cl, the energy-independent transhydrogenase increased two to threefold. Comparable changes occurred in NAD(P)+-linked glutamate dehydrogenase. NH4Cl concentrations of 20 to 60 mM resulted in relatively constant specific activities for both enzymes. Higher exogenous NH4Cl, however, led to a decline in both activities. Isocitrate dehydrogenase, another potential source of cellular NADPH, was insensitive to NH4Cl limitation. Similar studies in the presence of glutamate and different exogenous NH4Cl concentrations again showed concerted effects on both enzymes. Growth on glutamate as the sole nitrogen source led to severe repression of both transhydrogenase and glutamate dehydrogenase. In Salmonella typhimurium, both enzymes were unaffected by limiting NH4Cl or growth on glutamate as the sole nitrogen source. Both were, however, repressed by growth on aspartate, a potential source of cellular glutamate. Coordinate changes in glutamate dehydrogenase and transhydrogenase were also evident in Klebsiella aerogenes, particularly under conditions in which glutamate dehydrogenase was regulated inversely to glutamate synthetase. Coordinate changes in glutamate dehydrogenase and transhydrogenase in enteric bacteria are discussed in terms of the possible involvement of the latter enzyme as a direct source of NADPH in the ammonia assimilation system.
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PMID:Coregulation of oxidized nicotinamide adenine dinucleotide (phosphate) transhydrogenase and glutamate dehydrogenase activities in enteric bacteria during nitrogen limitation. 678 21

Studies of the nitrogen nutrition and pathways of ammonia assimilation in Rhodocyclus purpureus and Rhodospirillum tenue have shown that these two seemingly related bacteria differ considerably in aspects of their nitrogen metabolism. When grown photoheterotrophically with malate as carbon source, R. purpureus utilized only NH4+ or glutamine as sole nitrogen sources and was unable to fix N2. By contrast, R. tenue was found to utilize a variety of amino acids as nitrogen sources and was a good N2 fixer. No nitrogenase activity was detected in cells of R. purpureus grown on limiting ammonia, whereas cells of R. tenue grown under identical conditions reduced acetylene to ethylene at high rates. Regardless of the nitrogen source supporting growth, extracts of cells of R. purpureus contained high levels of glutamate dehydrogenase, whereas R. tenue contained only trace levels of this enzyme. Alanine dehydrogenase activity was absent from both species. We conclude that R. purpureus is incapable of fixing molecular nitrogen and employs the glutamate dehydrogenase pathway as the primary means of assimilating NH4+ under all growth conditions. R. tenue, on the other hand, employs the glutamine synthetase/glutamate synthase pathway for the incorporation of NH4+ supplied exogenously or as the product of N2 fixation.
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PMID:Nitrogen metabolism in the phototrophic bacteria Rhodocyclus purpureus and Rhodospirillum tenue. 686 18


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