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)

A mutant (gltB) of Escherichia coli lacking glutamate synthase (GOGAT) was unable to utilize a wide variety of compounds as sole nitrogen source (e.g., arginine, proline, gamma-aminobutyrate, and glycine). Among revertants of these Asm- strains selected on one of these compounds (e.g., arginine, proline, or gamma-aminobutyrate) were those that produce glutamine synthetase (GS) constitutively (GlnC phenotype). These revertants had a pleiotropically restored ability to grow on compounds that are metabolized to glutamate. This suggested that the expression of the genes responsible for the metabolism of these nitrogen sources was regulated by GS. An examination of the regulation of proline oxidase confirmed this hypothesis. The differential sensitivities of GlnC and wild-type strains to low concentrations (0.1 mM) of the glutamine analog L-methionine-DL-sulfoximine supported the conclusion that the synthesis of a glutamine permease was also positively controlled by GS. During the course of this study we found that the reported position of the locus (gltB) for glutamate synthase is incorrect. We have relocated this gene to be 44% linked to the argG locus by P1 transduction. Further mapping has shown that the locus previously called aspB is in reality the gltB locus and that the "suppressor" of the aspB mutation (A. M. Reiner, J. Bacteriol. 97:1431-1436, 1969) is the locus for glutamate dehydrogenase (gdhA).
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PMID:gltB gene and regulation of nitrogen metabolism by glutamine synthetase in Escherichia coli. 2 35

The possible role of glutamate dehydrogenase, glutamate synthase, and glutamine synthetase in the regulation of enzyme formation in the gamma-aminobutyric acid (GABA) catabolic pathway of Escherichia coli K-12 was investigated. Evidence is presented indicating that glutamine synthetase acts as a positive regulator in the E. coli GABA control system. Mutations impairing glutamate synthase activity prevent the depression of the enzymes of the GABA pathway in ammonia-limited glucose media. However, mutations resulting in constitutive synthesis of glutamine synthetase (GlnC) restore the ability of the glutamate synthase-less mutants to grow in glucose-GABA media and result in depressed synthesis of the GABA enzymes. It is suggested that the loss of glutamate synthesis activity affects the GABA control system indirectly by lowering glutamine synthetase levels.
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PMID:Regulation of gamma-aminobutyric acid degradation in Escherichia coli by nitrogen metabolism enzymes. 2 37

Glutamate is a major source of energy for Fusobacterium species but its mode of catabolism has not hitherto been elucidated. Cell suspensions of F. nucleatum and F. varium, as representative species from the oral cavity and gastrointestinal tract, respectively, both decarboxylated position-labelled glutamate but by different pathways. 14CO2 was released only from C-5 by F. nucleatum whereas F. varium decarboxylated glutamate at either C-1 or C-5. In both species, 2 mols of glutamate fermented yielded 2 mols of acetate and 1 mol of butyrate, suggesting the possibility of three metabolic pathways: the 2-oxoglutarate, mesaconate and 4-aminobutyrate pathways. Enzymes representative of the three pathways were assayed for in cell-free extracts of fusobacteria. All species tested possessed high levels of both glutamate dehydrogenase and 2-oxoglutarate reductase, indicating the presence of the 2-oxoglutarate pathway. Enzymes representative of the mesaconate pathway were detected in F. sulci, F. ulcerans, F. mortiferum and F. varium, while the latter two species also possessed the 4-aminobutyrate pathway. The pathways of glutamate catabolism therefore bore no relationship to the site of isolation of the fusobacteria tested but instead correlated with their chemotaxonomic properties. Thus, F. varium, F. mortiferum, F. ulcerans and F. sulci, which possess a peptidoglycan structure based on diaminopimelic acid, have either two or three pathways for glutamate catabolism whereas F. nucleatum and other species that have a lanthionine-based murein metabolized glutamate solely by the 2-oxoglutarate pathway.
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PMID:Pathways of glutamate catabolism among Fusobacterium species. 167 5

One-step and two-step assay methods were developed for general aminotransferases (ATs) utilizing Glu and alpha-ketoglutarate (alpha-KG) as the donor and acceptor of the amino group, by coupling a glutamate dehydrogenase (GDH) reaction with the AT reactions. For instance, alpha-KG formed from Glu by AspAT is reduced and aminated back to Glu by GDH, which oxidizes NADPH corresponding to the amount of alpha-KG formed. In the reverse reaction, Glu formed from alpha-KG is oxidized and deaminated back to alpha-KG by GDH, which reduces NADP+ corresponding to the amount of Glu formed. In the one-step assay, both AT and GDH reactions are simultaneously carried out, and the decrease or increase in NADPH fluorescence is directly monitored in 1.0 ml of the reaction mixture for both forward and reverse reactions. In the two-step assay, an AT reaction is carried out and stopped once at the first step. Next, the alpha-KG or Glu formed is determined fluorometrically in a GDH reaction. In order to analyze partially purified or crude samples, the one-step assay is convenient for surveying the relative activities. The two-step assay is useful for analyzing the properties of enzymes and measuring activities under conditions approaching the optimum. AspAT can be replaced by other general ATs using enzyme-specific substrates in place of oxalacetate and Asp in the assay mixture. The present methods were successfully applied to four enzymes (Asp, alanine, gamma-aminobutyrate, and ornithine ATs) in tissue homogenates and a mitochondrial extract.
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PMID:One-step and two-step fluorometric assay methods for general aminotransferases using glutamate dehydrogenase. 260 38

Early iron deficiency in rat does not affect the weight or the protein, DNA, and RNA content but results in a slight reduction in gamma-aminobutyric acid (GABA) (13%, p less than 0.01) and glutamic acid (20%, p less than 0.001) content of the brain. The activities of the two GABA shunt enzymes, glutamate dehydrogenase and GABA-transaminase, and of the NAD+-linked isocitrate dehydrogenase (ICDH) were inhibited whereas the glutamic acid decarboxylase, mitochondrial NADP+-linked ICDH, and succinic dehydrogenase activities remained unaltered in brain. On rehabilitation with the iron-supplemented diet for 1 week, these decreased enzyme activities in brain attained the corresponding control values. However, the hepatic nonheme iron content increased to about 80% of the control, after rehabilitation for 2 weeks. A prolonged iron deficiency resulting in decreased levels of glutamate and GABA may lead to endocrinological, neurological, and behavioral alterations.
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PMID:Effect of early iron deficiency in rat on the gamma-aminobutyric acid shunt in brain. 287 Nov 28

Studies of various parameters of amino acid and catecholamine metabolism in human cerebral cortex have provided a number of biochemical markers that appear to delineate areas of focal epileptic activity. These observations have been consolidated further by investigations of a number of experimental models of epilepsy in animals. In appraising this data, it is important to take into consideration whether the tissue samples were obtained during an actual seizure state or in an interictal period. It is also important when possible to assess the extent of astrogliosis and neuronal loss. Sites of spontaneously active epileptic spiking in the cerebral neocortex have a somewhat different amino acid profile when compared to gray matter obtained from surrounding nonspiking gyri several centimeters away. There is an elevation in glycine content, a relative diminution in taurine, and a trend towards lowered glutamic acid levels. However, the concentrations of the eight amino acids measured appear in both the foci and surround to still be within the general range for normal tissue. Measurements of key enzymes involved in the synthesis and regulation of neurotransmitters provide a complementary method of evaluating functional changes in epileptic brain as they are generally less labile than their substrates. There is a moderate increase in the activity of glutamic acid dehydrogenase, an enzyme that plays an important role in the synthesis of glutamic acid from glucose. In some patients a decrease in glutamic acid decarboxylase has also been reported: this enzyme forms gamma-aminobutyric acid (GABA) from glutamic acid and is thus important for inhibition in the central nervous system. Moreover, there is a striking increase in the activity of tyrosine hydroxylase, the rate-limiting enzyme responsible for catecholamine synthesis. The possibility of a focal abnormality in catecholamine metabolism is reinforced by the simultaneous finding of a relative decrease in the number of alpha-1 postsynaptic receptor sites. An important marker of energy metabolism in neural tissue, Na+,K+-ATPase activity, has also been found to be decreased in actively spiking human cerebral cortex. Data from experimental animal foci produced by topical application of convulsant agents show a consistent drop in glutamic acid tissue content. This can be matched to an efflux of glutamic acid from the cortical surface, which in turn is proportional to the electrographic activity of the spike focus. In addition, there is often also a decrease in taurine and GABA in such foci, as well as an increase in the levels of a number of neutral amino acids.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Amino acid and catecholamine markers of metabolic abnormalities in human focal epilepsy. 287 18

2-Keto-3-fluoroglutaric acid prepared by acid hydrolysis of its diethyl ester is stable, as the free acid in aqueous solution at pH 2, and can be stored at -20 degrees C for several years. Both enantiomers are reduced by NADH in the presence of glutamate dehydrogenase (EC 1.4.1.2) to the two diastereomers of 3-fluoro-L-glutamate, which are stable at neutral pH and at high pH unless heated. 2-Keto-3-fluoroglutarate exists in solution almost entirely as a hydrate both at low and neutral pH. Both enantiomers of ketofluoroglutarate react with the pyridoxamine forms of aspartate, alanine and 4-aminobutyrate transaminases to give fluoride release. 2 mol of cosubstrate amino acid react for each mol of ketofluoroglutarate (KFG) when starting from the pyridoxamine form of the enzyme: 2 RCHNH2COOH + KFG + H2O----F- + NH4+ + glutamate + 2 RCOCOOH. Both diastereomers of fluoroglutamate are decarboxylated by glutamate decarboxylase (EC 4.1.1.15) with fluoride release: KFG + H2O----CO2 + F- + HCOCH2CH2COOH. By contrast, only one isomer of fluoroglutamate will react with the pyridoxal form of glutamate-oxalacetate transaminase to give fluoride release: HOOCCHNH2CHFCH2COOH + H2O----4F- + NH4+ + HOOCCOCH2CH2COOH. The enzymatic decarboxylation of 3-fluoroisocitrate produces only one enantiomer of ketofluoroglutarate, which is reduced to threo (2R,3R)-3-fluoroglutamate by NADH and glutamate dehydrogenase: [2R,3S]-HOOCCH(OH)CF(COOH)CH2COOH + NADP+----[3R]-KFG + CO2 + NADPH + H+. The proton, 13C, and 19F-NMR parameters of ketofluoroglutarate and the two fluoroglutamate diastereomers are presented. These molecules are useful probes of enzymatic mechanisms thought to involve carbanion intermediates.
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PMID:2-Keto-3-fluoroglutarate: a useful mechanistic probe of 2-keto-glutarate-dependent enzyme systems. 289 78

The metabolism of [15N]glutamate was studied with gas chromatography-mass spectrometry in rat brain synaptosomes incubated with and without glucose. [15N]Glutamate was taken up rapidly by the preparation, reaching a steady-state level in less than 5 min. 15N was incorporated predominantly into aspartate and, to a much lesser extent, into gamma-aminobutyrate. The amount of [15N]ammonia formed was very small, and the enrichment of 15N in alanine and glutamine was below the level of detection. Omission of glucose substantially increased the rate and amount of [15N]aspartate generated. It is proposed that in synaptosomes (a) the predominant route of glutamate nitrogen disposal is through the aspartate aminotransferase reaction; (b) the aspartate aminotransferase pathway generates 2-oxoglutarate, which then serves as the metabolic fuel needed to produce ATP; (c) utilization of glutamate via transamination to aspartate is greatly accelerated when flux through the tricarboxylic acid cycle is diminished by the omission of glucose; (d) the metabolism of glutamate via glutamate dehydrogenase in intact synaptosomes is slow, most likely reflecting restriction of enzyme activity by some unknown factor(s), which suggests that the glutamate dehydrogenase reaction may not be near equilibrium in neurons; and (e) the activities of alanine aminotransferase and glutamine synthetase in synaptosomes are very low.
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PMID:Glucose and synaptosomal glutamate metabolism: studies with [15N]glutamate. 290 Aug 79

To detect possible changes in the regulation of glutamate/gamma-aminobutyric acid (GABA) enzymes at the level of gene expression in a thioacetamide-induced rat model of acute hepatic encephalopathy, we have examined changes in the mRNAs of four glutamate/GABA enzymes by quantitative RNA blot hybridization analysis. Such changes could reflect cell adaptation to excess ammonia or some other associated metabolic stress. The mRNA levels of glutamate dehydrogenase (GDH) decreased similarly in three different brain regions, whereas those of glutamine synthetase (GS) and glutaminase (GA) increased. The mRNA levels of glutamate decarboxylase (GAD) were unchanged. The results indicate that some effect of liver damage, presumably hyperammonemia, affected the expression of some, but not all, genes associated with ammonia and glutamate metabolism in the brain. This adaptation of gene expression to secondary effects of ammonia on brain amino acid neurotransmitter metabolism or brain energy metabolism could play a role in the physiological changes observed in hepatic encephalopathy.
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PMID:Changes in glutamate-cycle enzyme mRNA levels in a rat model of hepatic encephalopathy. 290 33

The mechanism by which pentylenetetrazole provokes convulsions in animals has been investigated by measuring its influence in vitro on the activities of several enzymes of glutamate metabolism in rat brain homogenates. Pentylenetetrazole does not affect the specific activities of glutamine synthetase, glutaminase, or glutamate decarboxylase; it inhibits those of glutamate dehydrogenase and aspartate aminotransferase, and stimulates that of gamma-aminobutyric acid (GABA) aminotransferase. The overall consequence of the action of pentylenetetrazole on the activities of these enzymes should be an increase in the concentration of glutamate and a decrease in that of GABA. This modulation of glutamate and GABA metabolism by pentylenetetrazole could contribute to the triggering of convulsions.
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PMID:Pentylenetetrazole inhibits glutamate dehydrogenase and aspartate aminotransferase, and stimulates GABA aminotransferase in homogenates from rat cerebral cortex. 321 59


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