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)

1. The coenzyme preference of bovine liver glutamate dehydrogenase (GDH) was probed using dual wavelength spectroscopy and pairing the thionicotinamide analogues, S-NAD or S-NADP (which have absorbance maxima at 400 nm), with the natural coenzymes, NADP or NAD. 2. S-NAD and S-NADP were found to be good alternate substrates for GDH: the apparent Km's for the thioderivatives were similar to those of the corresponding natural coenzymes, the apparent Km's for glutamate were unaltered by the substitution of the thioderivatives, and the effects of inhibitors and activators on S-NAD or S-NADP kinetics were qualitatively the same as those found for NAD or NADP, respectively. 3. Dual wavelength assays paired NAD and S-NADP or S-NAD and NADP to study the simultaneous reduction of the two coenzymes. Conditions of increasing glutamate concentrations produced differential effects on the rates of the NAD vs NADP reactions, the result, with either nucleotide pair, promoting the NADP linked reaction. 4. Activators and inhibitors of the GDH reaction also showed differential effects upon the NAD vs NADP linked reaction rates in the dual wavelength assay. ADP and leucine, which activate both the NAD and the NADP linked reactions in single coenzyme assays, preferentially activate the NADP or S-NADP linked reactions in the dual nucleotide assays. GTP produced greater inhibition of the NAD or S-NAD linked reactions than of the NADP or S-NADP reactions while ATP inhibited NAD or S-NAD reactions and activated NADP or S-NADP reactions. The net effect of all metabolite modulators was to promote the NADP linked reaction by decreasing the activity ratios, v(NAD)/v(S-NADP) or v(S-NAD)/v(NADP). 5. The results are consistent with the suggestion that NADP is the preferred coenzyme for the oxidative deamination of glutamate by GDH even though the enzyme is capable of utilizing either coenzyme in vitro.
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PMID:Regulation of coenzyme utilization by bovine liver glutamate dehydrogenase: investigations using thionicotinamide analogues of NAD and NADP in a dual wavelength assay. 717 89

Ornithine metabolism is coupled to oxidative phosphorylation in isolated rat liver mitochondria. The pathway involving ornithine: alpha-ketoglutarate transaminase (OKT), glutamic semialdehyde dehydrogenase (GSDH), and glutamate dehydrogenase (GDH) with cycling of alpha-ketoglutarate-glutamate at the OKT reaction appears to be involved. Ornithine may be utilized by this pathway to sustain ATP levels during mitochondrial energy-deficiency states with resultant decreased urea-cycle flux and increased ammonia production. This pathophysiologic mechanism suggests that hyperammonemia is a consequence of an energy-deficiency state. Therapy directed toward alleviating the energy-deficiency state may be more beneficial than efforts to reduce ammonia levels.
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PMID:Urea cycle regulation: I. Coupling of ornithine metabolism to mitochondrial oxidative phosphorylation. 718 96

The reaction catalyzed by bovine L-glutamate dehydrogenase is subjected to allosteric activation by ADP. We have measured the thermodynamic parameters (delta G0, delta H0, delta S0, and delta Cp) of the formation of the various possible binary and ternary complexes formed between the enzyme, NADPH, and either ADP or its analogs, adenosine, AMP, and ATP. delta H0 and delta Cp have been measured by flow calorimetry; delta G0 values obtained by calorimetry itself, differences spectroscopy, or gel filtration have been selected on the basis of accuracy under the conditions required for the formation of each complex. The data are interpreted in terms of "interaction parameters," the differences between the thermodynamic parameters of the formation of a ternary complex and the sum of those of the two related binary complexes. Both adnosine and ATP appear to loosen the binding of NADPH by simply preventing a subsite interaction of NADPH. AMP appears to have only minor and probably secondary effects. The negative effect of the binding of ADP on that of NADPH, however, involves the formation of a new interaction, which is exothermic, entropy compensated, has a moderately large negative delta Cp, and does not occur in either binary complex.
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PMID:The thermodynamics of a negatively interacting allosteric effector system. The glutamate dehydrogenase . NADPH . ADP complexes. 718 37

1. Protein-free extracts of isolated rat-liver mitochondria contain 5.17 +/- 0.19 nmol ammonia/mg protein [cf. Harris, E. J. and Bassett, D. J. (1971) FEBS Lett. 19, 214-217]. 2. The ammonia found in the protein-free extracts does not originate from lysosomes contaminating the mitochondrial preparation. 3. When isolated mitochondria are incubated with ornithine, 14CO2 and a source of ATP a small amount of citrulline is formed. This amount is stoichiometrically equivalent to the ammonia that disappears from the extramitochondrial space, whereas the amount of ammonia found in the protein-free extracts of the mitochondria remains unchanged. Similar results were obtained when the reductive amination of 2-oxoglutarate was used as an ammonia-consuming reaction. 4. When isolated mitochondria are incubated under conditions such that the glutamate dehydrogenase and 3-hydroxybutyrate dehydrogenase reactions reach equilibrium, the thermodynamically active concentration of ammonia is not equal to the concentration measured in the protein-free extracts. 5. About 80% of the ammonia found in protein-free extracts of rat-liver mitochondria is derived from a component or components with a molecular weight of greater than or equal to 50,000. 6. Protein-free extracts of isolated rat-liver cells contain considerable amounts of ammonia. After digitonin fractionation this ammonia is found in the protein-free extract of the particulate fraction. 7. It is concluded that the ammonia found in protein-free extracts of rat-liver tissue is derived from a component or components in the mitochondria and is released during deproteinization.
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PMID:Origin of the ammonia found in protein-free extracts of rat-liver mitochondria and rat hepatocytes. 743 58

1. Addition of 4-dimethylaminophenol (DMAP) to suspensions of isolated rat kidney tubules increased extracellular lactate dehydrogenase (LDH) at concn. which did not markedly affect gluconeogenesis. ATP content was also decreased by DMAP but this did not occur until the membrane became permeable to LDH. There was no similar leakage of the mitochondrial enzyme glutamate dehydrogenase. 2. After i.v. injection of DMAP to rats in doses which did not inhibit gluconeogenesis, kidney glutathione was decreased and the urinary LDH was increased. DMAP was irreversibly bound to tissue in rat, with the highest binding in the kidney. The highest binding occurs in those tissues in which DMAP causes necrosis. 3. In isolated rat hepatocytes, DMAP caused toxic effects which were similar but less extensive than occur on addition of DMAP to kidney tubules. The formation of acid-soluble metabolites was higher in isolated rat hepatocytes (20 nmol/mg protein) than in rat kidney tubules (4 nmol/mg protein). DMAP-glucuronide and DMAP-sulphate comprised the major acid-soluble metabolites in both preparations; conjugates of DMAP with glutathione or cysteine were also found.
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PMID:Effects of 4-dimethylaminophenol in rat kidneys, isolated rat kidney tubules and hepatocytes. 744 27

The nicotinamide adenine dinucleotide phosphate (NADP)-dependent glutamate dehydrogenase (NADP-GDH) of Agaricus bisporus, a key enzyme in ammonia assimilation, was purified to apparent electrophoretic homogeneity with 27% recovery of the initial activity. The molecular weight of the native enzyme was 330 kDa. The enzyme is probably a hexamer, composed of identical subunits of 48 kDa. The isoelectric point of the enzyme was found at pH 4.8. The N-terminus appeared to be blocked. The enzyme was specific for NADP(H). The Km-values were 2.1, 3.2, 0.074, 27.0, and 0.117 mM for ammonia, 2-oxoglutarate, NADPH, L-glutamate, and NADP respectively. The pH optima for the amination and deamination reactions were found to be 7.6 and 9.0, respectively. The temperature optimum was 33 degrees C. The effect of several metabolites on the enzyme's activity was tested. Pyruvate, oxaloacetate, ADP, and ATP showed some inhibitory effect. Divalent cations slightly stimulated the aminating reaction. Antibodies raised against the purified enzyme were able to precipitate NADP-GDH activity from a cell-free extract in an anticatalytic immunoprecipitation test. Analysis of a Western blot showed the antibodies to be specific for NADP-GDH.
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PMID:Purification and characterization of NADP-dependent glutamate dehydrogenase from the commercial mushroom Agaricus bisporus. 776 94

Phosphate depletion (PD) in vivo causes a sundry of abnormalities in pancreatic islets including a rise in cytosolic calcium, low ATP content, reduced Ca2+ ATPase and Na(+)-K+ ATPase activity, and impaired insulin secretion in response to glucose or potassium. L-Leucine is a strong secretagogue that triggers insulin secretion by deamination to alpha-ketoisocaproic acid (KIC) and the subsequent metabolism of the latter to ATP and by the activation of glutamate dehydrogenase (GLDH), which acts on glutamate to generate alpha-ketoglutarate, the metabolism of which results in ATP production. The generation of ATP triggers events that lead to insulin secretion. It is not known whether PD impairs leucine-induced insulin secretion, and the cellular derangements that are involved in such an abnormality are not defined. These issues were studied in PD rats and in pair-weighed normal animals as controls. D-Leucine uptake by islets from PD rats is normal, but both leucine- and KIC-induced insulin secretions are impaired and the activity of branched-chain keto acid dehydrogenase, which facilitates the metabolism of KIC, is reduced. Both leucine and 2-aminobicyclo (2-2-1) haptene failed to stimulate GLDH and to augment the generation of alpha-ketoglutarate in the islets of PD rats. Also, the concentration of basal alpha-ketoglutarate was significantly higher in the islets of PD rats, suggesting that its metabolism is impaired. In addition, the activity of glutaminase is significantly reduced, an abnormality that would result in decreased production of glutamate, the substrate for GLDH. The data show that PD impairs leucine-induced insulin secretion.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Phosphate depletion impairs leucine-induced insulin secretion. 787 37

Hyperthermophiles are a recently discovered group of microorganisms that grow at and above 90 degrees C. They currently comprise over 20 different genera, and except for two novel bacteria, all are classified as Archaea. The majority of these organisms are obligately anaerobic heterotrophs that reduce elemental sulfur (S degree) to H2S. The best studied from a biochemical perspective are the archaeon, Pyrococcus furiosus, and the bacterium, Thermotoga maritima, both of which are saccharolytic. P. furiosus is thought to contain a new type of Entner-Doudoroff pathway for the conversion of carbohydrates ultimately to acetate, H2 and CO2. The pathway is independent of nicotinamide nucleotides and involves novel types of ferredoxin-linked oxidoreductases, one of which has tungsten, a rarely used element, as a prosthetic group. The only site of energy conservation is at the level of acetyl CoA, which is the presence of ADP and phosphate is converted to acetate and ATP in a single step. In contrast, T. maritima utilizes a conventional Embden-Meyerhof pathway for sugar oxidation. P. furiosus also utilizes peptides as a sole carbon and energy source. Amino acid oxidation is thought to involve glutamate dehydrogenase together with at least three types of novel ferredoxin-linked oxidoreductases which catalyze the oxidation of 2-ketoglutarate, aryl pyruvates and formaldehyde. One of these enzymes also utilizes tungsten. In P. furiosus, virtually all of the reductant that is generated during the catabolism of both carbohydrates and peptides is channeled to a cytoplasmic hydrogenase. This enzyme is now termed sulhydrogenase, as it reduces both protons to H2 and S degrees (or polysulfide) to H2S. S degrees reduction appears to lead to the conservation of energy in P. furiosus but not in T. maritima, although the mechanism by which this occurs is not known.
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PMID:Biochemical diversity among sulfur-dependent, hyperthermophilic microorganisms. 794 71

Chronic renal failure (CRF) is associated with a sundry of abnormalities in pancreatic islets including a rise in their cytosolic calcium, reduced ATP content, and impaired glucose-induced insulin secretion. The latter is also stimulated by amino acids (such as leucine), and the cellular processes involved in leucine-induced insulin secretion are different from those responsible for glucose-induced insulin release. The present study examined whether leucine-induced insulin secretion is also impaired in CRF and investigated the cellular derangements for such a potential abnormality. The results showed that leucine-induced insulin secretion is markedly reduced by islets from CRF animals, and this defect was prevented by parathyroidectomy (PTX) of the CRF animals or by their treatment with verapamil, an agent that blocks the action of parathyroid hormone (PTH) on the pancreatic islets. Both leucine uptake and alpha-ketoisocaproic acid-induced insulin secretion by islets from CRF rats are normal; however, both the activation of glutamate dehydrogenase (GLDH) by leucine or by 2-aminobicyclo-[2-2-1]-haptene and the utilization of alpha-ketoglutarate are impaired, and the maximal reaction rate (Vmax) of glutaminase is reduced. These derangements are corrected by PTX of CRF rats or by their treatment with verapamil. The data demonstrate that 1) CRF is associated with impaired leucine-induced insulin secretion, 2) this defect is due to the state of secondary hyperparathyroidism of CRF, and 3) the cellular derangements responsible for this defect involve abnormalities in the metabolism of leucine and derangements in the leucine-GLDH-alpha-ketoglutarate-glutaminase pathway of the islets.
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PMID:Abnormal leucine-induced insulin secretion in chronic renal failure. 797 90

The probable involvement of hepatic carbamyl-P in the reciprocal relationship between hepatic ureagenesis and glycogenesis from glucose was explored. Isolated perfused liver preparations from 48-h fasted rats were employed. Moderate (9.2 mM) and relatively high levels of glucose (34 mM) were perfused. Hepatic glycogenesis, glucose-6-P, carbamyl-P, and citrulline levels, hepatic urea formation, and ureagenesis based upon perfusate urea levels were measured. Experimental probes selected to modify hepatic ureagenesis and carbamyl-P production and utilization included: (a) NH4Cl, maintained at 5 mM by continuous infusion (NH4+ is a substrate for carbamyl-P synthase I and glutamate dehydrogenase); (b) norvaline, an inhibitor of ornithine transcarbamylase which catalyzes the first committed step in the urea cycle; and (c) ethoxyzolamide, an inhibitor of carbonic anhydrase which produces HCO3-, an essential substrate for carbamyl-P synthase I. NH4+ increased ureagenesis and decreased glycogenesis. The inclusion of norvaline with NH4+ decreased ureagenesis and increased glycogenesis. Ethoxyzolamide with or without NH4+ inhibited both ureagenesis and glycogenesis, and decreased the hepatic glucose-6-P level. Glycogenesis was greater at 34 mM than 9.2 mM glucose, increased in norvaline-containing preparations correlative with increased availability of carbamyl-P, and decreased when carbamyl-P formation was inhibited by ethoxyzolamide. Kinetic analysis indicated a Km, Glc of 31 mM for glucose phosphorylation preliminary to glycogenesis. Glycogen formation via the "indirect pathway" (i.e. involving extrahepatic glycolysis, transport of lactate to the liver, and glyconeogenesis therefrom) was quantitatively insufficient to account for the observed glycogenesis. Glucokinase is contraindicated by the inverse relationship between hepatic glycogenesis and ATP availability in the ethoxyzolamide-treated preparations. In contrast, carbamyl-P:glucose phosphotransferase activity of the glucose-6-phosphatase system has the characteristics to bridge hepatic ureagenesis and glycogenesis.
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PMID:Glycogenesis from glucose and ureagenesis in isolated perfused rat livers. Influence of ammonium ion, norvaline, and ethoxyzolamide. 813 5


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