Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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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)

The Neurospora crassa super-suppressor mutation, ssu-1, suppresses the auxotrophic phenotype of the mutant am(17) by inserting tyrosine at residue 313 of NADP-specific glutamate dehydrogenase, a position occupied in the wild type by glutamate. Two classes of am(17) revertants due to further mutation within the am gene have, respectively, tyrosine and leucine at residue 313. These replacements are consistent with a chain-terminating codon in am(17) of either the amber (UAG) or the ochre type (UAA), but are inconsistent with UGA. The Leu313 and Tyr313 variants of the enzyme have effective activity but are grossly different from the wild type in Michaelis constants (especially for ammonium) and heat stabilities at two different pH values. They show smaller but significant differences in these respects from each other.
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PMID:Amino acid replacements resulting from suppression and missense reversion of a chain-terminator mutation in Neurospora. 1 80

From the cell-free extract of fodder yeast Candida tropicalis NADP-specific glutamate dehydrogenase was isolated and partially purified (75-fold) by means of fractional precipitation by ammonium sulphate and ion-exchange chromatography on DEAE-cellulose. The preparation was investigated with the aid of polyacrylamide gel electrophoresis. Kinetic characteristics of the enzyme in the cell-free extract and partially purified preparation were derived.
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PMID:[Purification and properties of the NADP-specific glutamate dehydrogenase of Candida tropicalis feed yeasts]. 2 41

The constitution and control by the inorganic nitrogen source of glutamate dehydrogenases of some unicellular green algae have been studied. The Ankistrodesmus braunii and Scenedesmus obliquus cells contain two different glutamate dehydrogenases, one of which is NADP-specific, the other is active with both NAD and NADP. Their synthesis does not depend on the nitrogen source. The activity of NADP-specific glutamate dehydrogenase increases sharply during nitrogen starvation. In Chlorella pyrenoidosa 82 and Ch. ellipsoidea only one constitutive double specific glutamate dehydrogenase is observed. Its activity does not change depending on the nitrogen nutrition conditions. In the cells of the thermophylic Chlorella strain Chlorella sp. K. ammomium induces a de novo synthesis of NADP-specific glutamate dehydrogenase in addition to the constitutive double specific glutamate dehydrogenase. Thus, the algae tested contain constitutive double specific glutamate dehydrogenase. The NADP-specific enzyme is absent in two Chlorella strains, is constitutive in A. braunii and S. obliquus, and is ammonium-inducible in three thermophylic Chlorella strains.
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PMID:[Glutamate dehydrogenases of unicellular green algae: effects of nitrate and ammonium in vivo]. 2 79

The nicotinamide adenine dinucleotide phosphate-specific glutamate dehydrogenase (NADP-GDH) of Chlorella sorokiniana was purified 260-fold to electrophoretic homogeneity in six steps. Depending on the techniques used, the native enzyme appeared to have a molecular weight of 290,000 or 410,000 and to be composed of five to seven identical subunits with a molecular weight of 58,000. The amino acid composition of this enzyme was shown to differ considerably from that of the NAD-GDH in this organism. The NH2-terminal amino acid was unavailable to dansylation. All six cysteines in the native enzyme were in the free sulfhydryl form. The pH optima for the aminating and deaminating reactions were 7.2 and 9.2, respectively. The Km values for NH4+, alpha-ketoglutarate, NADPH, L-glutamate, and NADP+ were 68, 12, 0.13, and 0.038 mM, respectively. At low substrate concentrations, no cooperativity was seen; however, severe inhibition of enzyme activity was observed at high alpha-ketoglutarate concentrations. Nucleotides did not affect enzyme activity. Antiserum produced in rabbits to the subunits of the enzyme yielded a single precipitin band with the purified enzyme in Ouchterlony double-diffusion analysis. Immunoelectrophoresis was used to confirm the purity of the enzyme and also to quantify the amount of enzyme antigen. These studies indicate that the NADPH-GDH and NAD-GDH isozymes are distinct molecular species in this organism.
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PMID:Purification and properties of the inducible nicotinamide adenine dinucleotide phosphate-specific glutamate dehydrogenase from Chlorella sorokiniana. 2 61

When synchronous cells of the eucaryotic microorganism Chlorella sorokiniana growing in nitrate medium were challenged to synthesize an ammonium-inducible nicotinamide adenine dinucleotide phosphate-specific glutamate dehydrogenase (NADP-GDH) at frequent intervals during the cell cycle the initial rate of induction (i.e., enzyme potential) of this enzyme increased in an approximately linear manner until the period of DNA replication (i.e., S phase). During the S phase, NADP-GDH potential exhibited a positive rate change proportional to the step increase in DNA level. The timing of this rate change was insensitive to large changes in cellular growth rate. This rate change could be blocked within the first cell cycle by specific inhibition of DNA replication with 2'-deoxyadenosine. The approximately linear increase in NADP-GDH potential and also of total cellular protein observed before and after the S phase is proposed to be a result of the increasing photosynthetic capacity of the cell during the cell cycle.
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PMID:Regulation of initial rate of induction of nicotinamide adenine dinucleotide phosphate-specific glutamate dehydrogenase during the cell cycle of synchronous Chlorella. 2 62

The symbiotic, nitrogen-fixing bacterium Rhizobium sp. 32H1 is a specialized ammonium producer during symbiosis. However, during free-living growth, Rhizobium 32H1 assimilates ammonium very poorly. Two pathways of ammonium assimilation exist in enteric bacteria. One is mediated by glutamate dehydrogenase, and the other is mediated by glutamine synthetase-glutamate synthase. The former pathway is altogether inoperative in Rhizobium 32H1; the latter pathway operates at a slow rate and is under strict negative control by ammonium itself. Rhizobium 32H1 glutamine synthetase activity is modulated by both repression-derepression and reversible adenylylation. For a biochemical process lacking an alternative pathway, such a regulatory pattern exacerbates the very process. This suggests that Rhizobium 32H1 restricts its own ammonium assimilation to maximize the contribution of fixed nitrogen to the host plant during symbiosis.
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PMID:Control of ammonium assimilation in Rhizobium 32H1. 2 98

Initial-rate studies were made of the oxidation of L-glutamate by NAD+ and NADP+ catalysed by highly purified preparations of dogfish liver glutamate dehydrogenase. With NAD+ as coenzyme the kinetics show the same features of coenzyme activation as seen with the bovine liver enzyme [Engel & Dalziel (1969) Biochem. J. 115, 621--631]. With NADP+ as coenzyme, initial rates are much slower than with NAD+, and Lineweaver--Burk plots are linear over extended ranges of substrate and coenzyme concentration. Stopped-flow studies with NADP+ as coenzyme give no evidence for the accumulation of significant concentrations of NADPH-containing complexes with the enzyme in the steady state. Protection studies against inactivation by pyridoxal 5'-phosphate indicate that NAD+ and NADP+ give the same degree of protection in the presence of sodium glutarate. The results are used to deduce information about the mechanism of glutamate oxidation by the enzyme. Initial-rate studies of the reductive amination of 2-oxoglutarate by NADH and NADPH catalysed by dogfish liver glutamate dehydrogenase showed that the kinetic features of the reaction are very similar with both coenzymes, but reactions with NADH are much faster. The data show that a number of possible mechanisms for the reaction may be discarded, including the compulsory mechanism (previously proposed for the enzyme) in which the sequence of binding is NAD(P)H, NH4+ and 2-oxoglutarate. The kinetic data suggest either a rapid-equilibrium random mechanism or the compulsory mechanism with the binding sequence NH4+, NAD(P)H, 2-oxoglutarate. However, binding studies and protection studies indicate that coenzyme and 2-oxoglutarate do bind to the free enzyme.
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PMID:Kinetic studies of dogfish liver glutamate dehydrogenase. 3 53

The nitrogen source available to Diplodia maydis in vivo is reported to affect the severity of stalk rot in maize. Nitrate and (or) ammonium salts were tested for their effect on the type of nitrogen metabolism found in Diplodia maydis in vitro. The level of glutamate dehydrogenase remained essentially constant on either nitrogen salt but nitrate reductase was induced by growth on nitrate salts and was not extractable on ammonium salts. Properties of nitrate reductase reported here are similar to those reported for the higher plant and Neurospora crassa enzymes. Thr relationship of nitrogen metabolism in Diplodia maydis to Zea mays L. stalk rot is discussed.
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PMID:Nitrogen-metabolizing enzymes of Diplodia maydis, a Zea mays L. stalk rot causing fungus. 3 73

The regulation of the glutamate dehydrogenases was investigated in wild-type Neurospora crassa and two classes of mutants altered in the assimilation of inorganic nitrogen, as either nitrate or ammonium. In the wild-type strain, a high nutrient carbon concentration increased the activity of reduced nicotinamide adenine dinucleotide phosphate (NADPH)-glutamate dehydrogenase and decreased the activity of reduced nicotinamide adenine dinucleotide (NADH)-glutamate dehydrogenase. A high nutrient nitrogen concentration had the opposite effect, increasing NADH-glutamate dehydrogenase and decreasing NADPH-glutamate dehydrogenase. The nit-2 mutants, defective in many nitrogen-utilizing enzymes and transport systems, exhibited low enzyme activities after growth on a high sucrose concentration: NADPH-glutamate dehydrogenase activity was reduced 4-fold on NH(4)Cl medium, and NADH-glutamate dehydrogenase, 20-fold on urea medium. Unlike the other affected enzymes of nit-2, which are present only in basal levels, the NADH-glutamate dehydrogenase activity was found to be moderately enhanced when cells were grown on a low carbon concentration. This finding suggests that the control of this enzyme in nit-2 is hypersensitive to catabolite repression. The am mutants, which lack NADPH-glutamate dehydrogenase activity, possessed basal levels of NADH-glutamate dehydrogenase activity after growth on urea or l-aspartic acid media, like the wild-type strain, and possessed moderate levels (although three- to fourfold lower than the wild-type strain) on l-asparagine medium or l-aspartic acid medium containing NH(4)Cl. These regulatory patterns are identical to those of the nit-2 mutants. Thus, the two classes of mutants exhibit a common defect in NADH-glutamate dehydrogenase regulation. Double mutants of nit-2 and am had lower NADH-glutamate dehydrogenase activities than either parent. A carbon metabolite is proposed to be the repressor of NADH-glutamate dehydrogenase in N. crassa.
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PMID:Regulation of glutamate dehydrogenases in nit-2 and am mutants of Neurospora crassa. 3 17

Earlier studies indicated that the gene of an ammonium-inducible glutamate dehydrogenase (GDH) was inducible throughout the cell cycle and was expressible shortly after replication early in the S-phase in synchronous Chlorella cells growing at a rate of 13% per h in the absence of inducer. In the present study, synchronous cells cultured at the same growth rate in the continuous presence of inducer accumulated this enzyme in a linear manner, with a positive rate change observed late instead of early in the S-phase. At a growth rate of 26% per h, the positive rate change appeared to be displaced to 1.5 h before the S-phase in the next cell cycle. With 2'-deoxyadenosine, an in vivo inhibitor of deoxyribonucleic acid (DNA) synthesis, the magnitude of the positive rate change was shown to be proportional to the relative increase in DNA in the previous cell cycle. Collectively, these data support the idea that expression of newly replicated genes of this enzyme can be delayed into the subsequent cell cycle in cells in the continuous presence of inducer. Studies with cycloheximide indicated that the inducible GDH and another GDH isozyme were stable in fully induced cells in the absence of protein synthesis. However, after ammonium was removed from the culture medium, the activity of the inducible GDH decreased rapidly in vivo, with a half-time of 5 to 10 min at 38.5 degrees C, whereas the rate of accumulation of the other GDH isozyme did not change. Addition of cycloheximide, at the time of inducer removal, prevented this loss in activity of the inducible GDH. The inability to rescue the activity of the inducible GDH, by readdition of ammonium during the deinduction period, indicates that this enzyme probably underwent irreversible inactivation and/or proteolytic degradation.
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PMID:Regulation of accumulation and turnover of an inducible glutamate dehydrogenase in synchronous cultures of Chlorella. 4 86


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