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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 reaction of glutamate dehydrogenase and glutamate (gl) with NAD+ and NADP+ has been studied with stopped-flow techniques. The enzyme was in all experiments present in excess of the coenzyme. The results indicate that the ternary complex (E-NAD(P)H-kg) is present as an intermediate in the formation of the stable complex (E-NAD(P)H-gl). The identification of the complexes is based on their absorption spectra. The binding of the coenzyme to (E-gl) is the rate-limiting step in the formation of (E-NAD(P)H-kg) while the dissociation of alpha-ketoglutarate (kg) from this complex is the rate-limiting step in the formation of (E-NAD(P)H-gl). The Km for glutamate was 20-25 mM in the first reaction and 3 mM in the formation of the stable complex. The Km values were independent of the coenzyme. The reaction rates with NAD+ were approximately 50% greater than those with NADP+. Furthermore, high glutamate concentration inhibited the formation of (E-NADH-kg) while no substrate inhibition was found with NADP+ as coenzyme. ADP enhanced while GTP reduced the rate of (E-NAD(P)H-gl) formation. The rate of formation of (E-NAD(P)H-kg) was inhibited by ADP, while it increased at high glutamate concentration when small amounts of GTP were added. The results show that the higher activity found with NAD+ compared to NADP+ under steady-state assay conditions do not necessarily involve binding of NAD+ to the ADP activating site of the enzyme. Moreover, the substrate inhibition found at high glutamate concentration under steady-state assay condition is not due to the formation of (E-NAD(P)H-gl) as this complex is formed with Km of 3 mM glutamate, and the substrate inhibition is only significant at 20-30 times this concentration.
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PMID:Formation of transient complexes in the glutamate dehydrogenase catalyzed reaction. 0 39

The extracellular proteinase of Staphylococcus aureus strain V8 was used to digest the NADP-specific glutamate dehydrogenase of Neurospora crassa. Of 35 non-overlapping peptides expected from the glutamate content of the polypeptide chain, 29 were isolated and substantially sequenced. The sequences obtained were valuable in providing overlaps for the alignment of about two-thirds of the sequences found in tryptic peptides [Wootton, J. C., Taylor, J, G., Jackson, A. A., Chambers, G. K. & Fincham, J. R. S. (1975) Biochem. J. 149, 739-748]. The blocked N-terminal peptide of the protein was isolated. This peptide was sequenced by mass spectrometry, and found to have N-terminal N-acetylserine by Howard R. Morris and Anne Dell, whose results are presented as an Appendix to the main paper. The staphylococcal proteinase showed very high specificity for glutamyl bonds in the NH4HCO3 buffer used. Partial splits of two aspartyl bonds, both Asp-Ile, were probably attributable to the proteinase. No cleavage of glutaminyl or S-carboxymethylcysteinyl bonds was found. Additional experimental detail has been deposited as Supplementary Publication SUP 50053 (5 pages) with the British Library (Lending Division), Boston Spa, Wetherby, W. Yorkshire LS23 7BQ, U.K, from whom copies may be obtained under the terms given in Biochem. J. (1975) 1458 5.
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PMID:The amino acid sequence of Neurospora NADP-specific glutamate dehydrogenase. Peptides from digestion with a staphylococcal proteinase. 0 Oct 1

The kinetic properties of the constitutive double specific glutamate dehydrogenase (NAD(P)--GDH) and the inducible NADP-specific glutamate dehydrogenase (NADP--GDH) of Chlorella pyrenoidosa Pringsheim 82T (thermophilic strain) in a deaminating reaction have been studied. NAD(P)-GDH behaves in a deamination as a Michaelis-Menten enzyme. NADP-GDH displays some lag-period before a steady-state phase. The duration of this lag depends on a substrate concentration. Besides that, an effect of all the substrates on a heat inactivation of both GDH and a product inhibition have been studied. All the substrates except the reduced co-factors protect effectively GDH from the heat inactivation, especially the thermolabille NADP-GDH. On the contrary, NAD(P)-H promote the heat inactivation of both GDH. The product inhibition analysis shows that the inducible NADP-GDH acts in vivo as a synthetic enzyme. In the previous paper (V. R. Shatilov et all., 1974, Dokl. Acad. Nauk USSR, 216,223) it was shown for the constitutive GDH that p-CMB strongly inhibited a desamination and slightly (if any) affect an amination. It this paper it is shown that action of p-CMB on the amination depends on the presence of NAD+ (not NADP+ or L-glutamate). p-CMB and NAD+ affect tha amination in a strongly sunergetic manner. Some suggestions about the intracellular localization of chlorella GDH are made.
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PMID:[Comparative study of glutamate dehydrogenases of Chlorella]. 0 35

Isophthalic acid, 5-carboxy-, 5-hydroxy-, 5-methoxy-, 5-fluoro-, 5-bromo-, 5-cyano-, and 5-methylisophthalic acid were inhibitors competitive with L-glutamate for bovine liver glutamate dehydrogenase. The extent of inhibition by the derived compounds was not much greater than that obtained with the parent compound, isophthalic acid. A plot of pKi versus pH showed the presence of an ionizable group (pKa 7.4-7.8) at the enzyme active site which interacted with the substitutent at the 5 position of the substituted isophthalates.
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PMID:Synthesis of 5-substituted isophthalic acids and competitive inhibition studies with bovine liver glutamate dehydrogenase. 0 35

Glutamate synthase from Escherichia coli K-12 exhibits NH3-dependent activity. NH3-dependent activity is increased approximately 5-fold in apoglutamate synthase lacking flavin and non-heme iron. Whereas glutamine plus 2-oxoglutarate have the capacity to reoxidize the chemically reduced flavoenzyme, no such reoxidation is obtained with 2-oxoglutarate plus NH3. These results establish that the glutamine- and NH3-dependent syntheses of glutamate occur by different pathways of electron transfer from NADPH. The NH3-dependent activity of native and apoglutamate synthase exhibits similar catalytic properties. Some properties of apoglutamate synthase are similar to those of glutamate dehydrogenase. These properties include pH optima for synthesis and oxidative deamination of glutamate, inactivation by alkylating reagents and p-mercuribenzoate, an enhanced rate of inactivation by alkylating reagents and p-mercuribenzoate at low pH, 2-oxoglutarate protection against inactivation by p-mercuribenzoate, and reactivation of p-mercuribenzoate-treated enzyme by 2-mercaptoethanol. 2-Oxoglutarate protects against alkylation of glutamate synthase by iodo [1-14C]acetamide and reduces incorporation of methyl [1-14C]carboxamide into the small subunit of the enzyme.
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PMID:Properties of apoglutamate synthase and comparison with glutamate dehydrogenase. 0 50

Nitrogenase biosynthesis in Klebsiella pneumoniae including mutant strains, which produce nitrogenase in the presence of NH+4 (Shanmugam, K.T., Chan, Irene, and Morandi, C. (1975) Biochim. Biophys. Acta 408, 101--111) is repressed by a mixture of L-amino acids. Biochemical analysis shows that glutamine synthetase activity in strains SK-24, SK-28, and SK-29 is also repressed by amino acids, with no detectable effect on glutamate dehydrogenase. Among the various amino acids, L-glutamine in combination with L-aspartate was found to repress nitrogenase biosynthesis completely. In the presence of high concentrations of glutamine (1 mg/ml) even NH+4 repressed nitrogenase biosynthesis in the strains SK-27, SK-37, SK-55 and SK-56. Under these conditions, increased glutamate dehydrogenase activity was also detected. Physiological studies show that nitrogenase derepressed strains are unable to utilize NH+4 as sole source of nitrogen for biosynthesis of glutamate for biosynthesis of glutamate, whereas back mutations leading to NH+4 utilization results in sensitivity to repression by NH+4. These findings suggest that amino acids play an important role as regulators of nitrogen fixation.
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PMID:Amino acids as repressors of nitrogenase biosynthesis in Klebsiella pneumoniae. 0 1

We have isolated mutant strains (nit) of Salmonella typhimurium that are defective in nitrogen metabolism. They have a reduced ability to use a variety of compounds including glutamate, proline, arginine, N-acetyl-glucosamine, alanine, and adenosine as sole nitrogen source. In addition, although they grow normally on high concentrations of ammonium chloride (greater than 1 mM) as nitrogen source, they grow substantially more slowly than wild type at low concentrations (less than 1 mM). We postulated that the inability of these strains to utilize low concentrations of ammonium chloride accounts for their poor growth on other nitrogen sources. The specific biochemical lesion in strains with a nit mutation is not known; however, mutant strains have no detectable alteration in the activities of glutamine synthetase, glutamate synthetase, or glutamate dehydrogenase, the enzymes known to be involved in assimilation of ammonia. A nit mutation is suppressed by second-site mutations in the structural gene for glutamine synthetase (glnA) that decrease glutamine synthetase activity.
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PMID:Mutant strains (nit) of Salmonella typhimurium with a pleiotropic defect in nitrogen metabolism. 1 Feb 75

NH+4 excretion was undetectable in N2-fixing cultures of Rhodospirillum 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 (greater than 40 mumoles NH+4/mg cell protein in 6 days) or L-glutamate (greater than 60 mumoles NH+4/ mg cell protein in 6 days) was added to the cultures together with MSX. Biochemical analysis revealed that R. 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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PMID:Photoproduction of ammonium ion from N2 in Rhodospirillum rubrum. 1 53

Kinetic analyses done with cell-free extracts of this basidiomycete fungus showed that the NADP-linked glutamate dehydrogenase exhibited positively co-operative interactions with the substrates 2-oxoglutarate and NADPH, negatively co-operative kinetics with NADP+ and was extremely sensitive to inhibition of deamination activity by ammonium and/or ammonia. The NAD-linked enzyme showed positive co-operativity with NADH, Michaelis-Menten kinetics with all other substrates and was subject only to mild inhibitions by the reaction products. Considered together with the values of the Michaelis constants, these results indicate that the former enzyme is primarily concerned with the amination of 2-oxoglutarate when the concentration of this substrate exceeds about 4 mM, while the NAD-linked enzyme is able to aminate or deaminate as metabolic conditions require. Synthesis of both enzymes was repressed by addition of carbamyl phosphate or N-acetyl-glutamate to mycelial cultures growing in media containing glucose and ammonium as carbon and nitrogen sources. Growth in media containing urea results in repression of the NADP-linked glutamate dehydrogenase and derepression of the NAD-linked enzyme. Such results indicate a connexion between the glutamate dehydrogenases and the urea cycle. It is suggested that under normal conditions of growth on complex media nitrogen is assimilated in the form of amino acids and that the glutamate dehydrogenases act in support of transaminases to allow this process to continue, and in support of the urea cycle to allow the disposal of excess nitrogen.
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PMID:Factors affecting the amount and the activity of the glutamate dehydrogenases of Coprinus cinereus. 1 62

Glutamate synthase was purified about 250-fold from Thiobacillus thioparus and was characterized. The molecular weight was estimated as 280,000 g/mol. The enzyme showed absorption maxima at 280, 380, and 450 nm and was inhibited by Atebrin, suggesting that T. thioparus glutamate synthase is a flavoprotein. The enzyme activity was also inhibited by iron chelators and thiolbinding agents. The enzyme was specific for reduced nicotinamide adenine dinucleotide phosphate (NADPH) and alpha-ketoglutarate, but L-glutamine was partially replaced by ammonia as the amino donor. The Km values of glutamate synthase for NADPH, alpha-ketoglutarate, and glutamine were 3.0 muM, 50 muM, and 1.1 mM, respectively. The enzyme had a pH optimum between 7.3 and 7.8. Glutamate synthase from T. thioparus was relatively insensitive to feedback inhibition by single amino acids but was sensitive to the combined effects of several amino acids. Enzymes involved in glutamate synthesis in T. thioparus were studied. Glutamine synthetase and glutamate synthase, as well as two glutamate dehydrogenases (NADH and NADPH dependent), were present in this organism. This levels of glutamate synthase and glutamate dehydrogenase were similar in T. thioparus grown on 0.7 or 7.0 mM ammonium sulfate. The sum of the activities of both glutamate dehydrogenases was only 1/25 of that of glutamate synthase under the assay conditions. It was concluded that the glutamine pathway is important for ammonia assimilation in this autotrophic bacterium.
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PMID:Purification and properties of glutamate synthase from Thiobacillus thioparus. 1 19


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