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 ATP production rate in isolated skeletal muscle mitochondria was measured with a bioluminescence method, before and during erythropoietin treatment, in 21 anaemic haemodialysis patients. In addition, the concentrations of ATP, phosphocreatine and total creatine and the ratio of alkali-soluble protein to DNA were determined in skeletal muscle. Maximal oxygen uptake and maximal exercise capacity were determined on a bicycle ergometer. 2. The results unexpectedly showed a 35% higher mitochondrial ATP production rate in the patients before erythropoietin treatment than in sedentary control subjects. On the other hand, mitochondrial density, as measured by the activity of the matrix enzyme glutamate dehydrogenase, was the same in the patients as in the sedentary control group. After 1 year on maintenance erythropoietin treatment, the ATP production rate per kg of muscle decreased in five out of seven patients and reached the same level as in the sedentary control subjects. The ratio between ATP production rate and glutamate dehydrogenase activity was on average 40% higher in the patients at the start and decreased towards the control level in six out of seven patients after 1 year on maintenance erythropoietin treatment. When related to the mitochondrial protein content, a significant reduction in the ATP production rate was observed. 3. The ratio of alkali-soluble protein to DNA in skeletal muscle and the concentrations of ATP, phosphocreatine and total creatine in skeletal muscle at rest were normal in the patients and did not change during the study. The maximal aerobic power improved by 25% after the correction of anaemia.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:ATP production in isolated muscle mitochondria from haemodialysis patients: effects of correction of anaemia with erythropoietin. 166 51

Patients with McArdle's disease (myophosphorylase deficiency) cannot use muscle glycogen as an energy source during exercise. They therefore are an ideal model to learn about the metabolic adaptations which develop during endurance exercise leading to glycogen depletion. This review summarizes the current knowledge of ammonia and amino acid metabolism in these patients and also adds several new data. During incremental exercise tests in patients with McArdle's disease, forearm venous plasma ammonia concentration rises to a value between 200 and 500 microM. Femoral arteriovenous difference studies show that muscle produces the ammonia. The leg release of both ammonia and glutamine (in mumol/min) has been estimated to be five- to tenfold larger in one of these patients than in healthy individuals exercising at comparable relative work load. Patients with McArdle's disease have a larger uptake of branched-chain amino acids (BCAA) by exercising leg muscles and show a more rapid activation of the muscle branched-chain 2-oxo acid dehydrogenase complex, a key enzyme in the degradation of the BCAA. In general, supplements of BCAA taken before the exercise test lead to a deterioration of exercise performance and a higher increase in heart rate and plasma ammonia during exercise, whereas supplements of branched-chain 2-oxo acids improve exercise performance and lead to a smaller increase in heart rate and plasma ammonia. At constant power output, patients with McArdle's disease show a rapid increase in heart rate and exertion perceived in the exercising muscles, which peak within 10 min after the start of exercise and then fall again ("second wind"). Peak heart rate and peak exertion coincide with a peak in plasma ammonia. Ammonia production during exercise in these patients is estimated to exceed the reported breakdown of ATP to IMP and therefore most likely originates from the metabolism of amino acids. Deamination of amino acids via the reactions of the purine nucleotide cycle and glutamate dehydrogenase are possible pathways. Deamination of glutamine, released by muscle, by glutaminase present in the endothelial cells of the vascular system may also contribute to the ammonia production. The observations made in these patients have led to the hypothesis that excessive acceleration of the metabolism of BCAA drains 2-oxoglutarate in the primary aminotransferase reaction and thus reduces flux in the citric acid cycle and impedes aerobic oxidation of glucose and fatty acids. This draining effect is normally counteracted by the anaplerotic conversion of muscle glycogen to citric acid cycle intermediates, a reaction which is severely hampered in these patients due to the glycogen breakdown defect.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Metabolism of branched-chain amino acids and ammonia during exercise: clues from McArdle's disease. 219 89

1. On transferring Clostridium symbiosum glutamate dehydrogenase from pH 7 to assay mixtures at pH 8.8, reaction time courses showed a marked deceleration that was not attributable to the approach to equilibrium of the catalysed reaction. The rate became approximately constant after declining to 4-5% of the initial value. Enzyme, stored at pH 8.8 and assayed in the same mixture, gave an accelerating time course with the same final linear rate. The enzyme appears to be reversibly converted from a high-activity form at low pH to a low-activity form at high pH. 2. Re-activation at 31 degrees C upon dilution from pH 8.8 to pH 7 was followed by periodic assay of the diluted enzyme solution. At low ionic strength (5 mM-Tris/HCl), no re-activation occurred, but various salts promoted re-activation to a limiting rate, with full re-activation in 40 min. 3. Re-activation was very temperature-dependent and extremely slow at 4 degrees C, suggesting a large activation energy. 4. 2-Oxoglutarate, glutarate or succinate (10 mM) accelerated re-activation; L-glutamate and L-aspartate were much less effective. 5. The monocarboxylic amino acids alanine and norvaline appear to stabilize the inactive enzyme: 60 mM-alanine does not promote re-activation, and, as substrates at pH 8.8 for enzyme stored at pH 7, alanine and norvaline give progress curves showing rapid complete inactivation. 6. Mono- and di-nucleotides (AMP, ADP, ATP, NAD+, NADH, NADP+, CoA, acetyl-CoA) at low concentrations (10(-4)-10(-3) M) enhance re-activation at pH 7 and also retard inactivation at pH 8.8. 7. The re-activation rate is independent of enzyme concentration: ultracentrifuge experiments show no changes in molecular mass with or without substrates. 8. The activation-inactivation appears to be due to a slow pH-dependent conformational change that is sensitively responsive to the reactants and their analogues.
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PMID:A pH-dependent activation-inactivation equilibrium in glutamate dehydrogenase of Clostridium symbiosum. 224 20

Sodium valproate, a commonly used anticonvulsant agent, is a simple branched-chain fatty acid which interferes with beta-oxidation and ammonia metabolism in most patients, with hepatotoxic consequences in some cases. Rat liver mitochondria incubated with valproate displayed time-dependent inhibitions of state 3 oxidation rates with all the substrates tested, but most markedly with glutamate, pyruvate, alpha-ketoglutarate and acylcarnitines (Ki = 125 microM with glutamate and palmitoylcarnitine, and 24 microM with pyruvate). The inhibition of glutamate appeared to be specifically directed against the glutamate dehydrogenase pathway of this oxidation. Valproate was less effective when added to uncoupled mitochondria, suggesting the formation of an inhibitory species by an ATP-dependent mechanism. Mitochondria from clofibrate-treated rats were less sensitive to valproate inhibition. Neither fasting nor the presence of 1 mM L-carnitine affected the inhibition of beta-oxidation. The branched-chain isomer, 2-ethylhexanoic acid, had similar effects to valproate, but the straight-chain octanoic acid was totally different in its spectrum of actions on mitochondria. The data support the theory that valproate may inhibit by sequestration of CoA as valproyl-CoA, but also suggest that there are other mechanisms responsible for some of the inhibitions. Furthermore, it argued that while mitochondrial respiration is decreased, valproate is not an inhibitor of oxidative phosphorylation per se.
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PMID:In vitro effects of eight-carbon fatty acids on oxidations in rat liver mitochondria. 224 43

5'-p-Fluorosulfonylbenzoyladenosine (FSBA) is a useful reagent for the affinity labeling of adenine nucleotide binding proteins. We have developed an immunochemical approach to the detection of proteins that have been covalently modified with FSBA, which provides an alternative to the use of a radiolabeled ligand. Antibodies have been prepared against FSBA-modified glutamate dehydrogenase and purified by chromatography on ATP-agarose. The resulting affinity-purified antibodies react on Western blots only with proteins that have been labeled previously with the affinity reagent. The degree of immunoreactivity on Western blots correlates well with the extent of covalent modification as shown by studies on the modification and inhibition of the catalytic subunit of cAMP-dependent protein kinase. In crude cellular extracts, numerous proteins can be labeled with FSBA and then detected by using this approach. The labeling and subsequent detection of these proteins can be blocked by including an excess of MgATP, which competes with FSBA for nucleotide-binding sites. The labeling of specific proteins in crude mixtures is saturable, as shown by labeling studies of p56lck, a protein-tyrosine kinase that is abundantly expressed in membranes from the T lymphoma cell line LSTRA.
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PMID:Immunochemical detection of adenine nucleotide-binding proteins with antibodies to 5'-p-fluorosulfonylbenzoyladenosine. 228 46

In the presence of Mg2+, pure glutamate dehydrogenase is more reactive with NADPH than with NADH and is markedly activated by elevations in the ADP/ATP ratio or the addition of leucine. Because these are properties of glutamate dehydrogenase in mitochondria but not properties of the pure enzyme studied in the absence of Mg2+, Mg2+ could be a ligand that confers upon glutamate dehydrogenase the regulatory properties of this enzyme found in situ. In the absence of the allosteric activators ADP, leucine, or succinyl-CoA, Mg2+ is an inhibitor and increases product inhibition by alpha-ketoglutarate in the forward reaction and substrate inhibition by alpha-ketoglutarate in the reverse reaction. However, the allosteric activators convert Mg2+ from an inhibitor into an activator of the forward reaction. In the reverse reaction, ADP also converts Mg2+ from an inhibitor into an activator and leucine eliminates inhibition by Mg2+. Because Mg2+ is an inhibitor in the absence of activator that also increases inhibition by alpha-ketoglutarate, whereas in the presence of activator Mg2+ has no effect or is itself an activator, Mg2+ magnifies the effect of the activator, and magnification increases with increases in the concentration of alpha-ketoglutarate. Leucine and its analog 2-aminobicyclo (2.2.1) heptane 2-carboxylic acid (BCH) have almost identical effects on both human and bovine glutamate dehydrogenase in both the presence and absence of Mg2+. However, advantages of BCH over leucine as a potential pharmacological activator of glutamate dehydrogenase are that BCH is not metabolized and, unlike leucine, BCH does not inhibit ornithine transcarbamylase. Isoleucine and valine alone have little effect on human glutamate dehydrogenase, but isoleucine slightly inhibits the enzyme in the presence of leucine.
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PMID:Regulation of glutamate dehydrogenase by Mg2+ and magnification of leucine activation by Mg2+. 235 6

Mitochondrial ATP production (MAPR) was determined using a bioluminescence method in mitochondrial preparations of human skeletal muscle. We obtained muscle samples from 21 healthy subjects using the percutaneous muscle biopsy technique. The subjects were grouped according to their degree of physical activity, i.e., from sedentary to highly active. The MAPR for each subject was related to the mitochondrial protein content and to the activity of glutamate dehydrogenase (GDH) estimated in muscle homogenates and in isolated mitochondria. With the use of GDH as a reference base, the MAPR could be expressed per muscle mass. MAPR was determined for different individual substrates and also for the combination of pyruvate, palmitoyl-carnitine, alpha-ketoglutarate, and malate (MAPRPPKM). The MAPR observed was higher for the combination of substrates than for any individual substrate tested. The relation between mitochondrial ATP production rate and GDH activity was the same for all subjects irrespective of physical activity status, but MAPRPPKM/kg muscle varied from 6.6 +/- 1.3 mmol.min-1.kg-1 in sedentary subjects to 11.0 +/- 2.2 in highly active subjects. The present method, which uses 50 mg of muscle tissue, enables mitochondrial function to be estimated in healthy subjects or patients with mitochondrial disorders.
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PMID:ATP production rate in mitochondria isolated from microsamples of human muscle. 238 13

The effect of nucleotides: AMP, cAMP, ADP, ATP, GDP and GTP, on glutamate dehydrogenase (GDH) purified from the mealworm fat body was studied. Guanine nucleotides and ATP inhibited the enzyme strongly in both directions. GDH was partially protected from the inhibition by the addition of ADP to an assay medium. AMP and cAMP activated the enzyme slightly. The concerted effects of ADP and ATP indicate the importance of adenylate energy charge in the regulation of fat body GDH. It is suggested that GDH may play amphibolic role in the fat body and that the direction of GDH catalysed reaction is under strong influence of nucleotides. The enzyme may synthesize glutamate at high energy charge, but when the energy reserves are low, it oxidizes glutamate.
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PMID:The effect of nucleotides on glutamate dehydrogenase from the mealworm fat body. 245 16

Streptomyces fradiae has two chromatographically distinct forms of glutamate dehydrogenase (GDH): one GDH utilizes NAD as coenzyme, the other uses NADP. The intracellular level of both GDHs is strongly regulated by the nitrogen source in the growth medium. NADP-dependent GDH was purified to homogeneity from crude extracts of S. fradiae. The Mr of the native enzyme was determined to be 200,000 by size-exclusion high-performance liquid chromatography whereas after sodium dodecyl sulphate-polyacrylamide gel electrophoresis one major band of Mr 49,000 was found, suggesting that the enzyme is a tetramer. The enzyme was highly specific for the substrates 2-oxoglutarate and L-glutamate, and required NADP, which could not be replaced by NAD, as a cofactor. The pH optimum was 9.2 for oxidative deamination of glutamate and 8.4 for reductive amination of 2-oxoglutarate. The Michaelis constants (Km) were 28.6 mM for L-glutamate and 0.12 mM for NADP. Km values for reductive amination were 1.54 mM for 2-oxoglutarate, 0.07 mM for NADPH and 30.8 mM for NH+4. The enzyme activity was significantly reduced by adenine nucleotides, particularly ATP.
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PMID:Purification and properties of NADP-dependent glutamate dehydrogenase from Streptomyces fradiae. 256 88

Pathways of ammonia assimilation into glutamic acid were investigated in ammonia-grown and N2-fixing Clostridium kluyverii and Clostridium butyricum by measuring the specific activities of glutamate dehydrogenase, glutamine synthetase, and glutamate synthase. C. kluyverii had NADPH-glutamate dehydrogenase with a Km of 12.0 mM for NH4+. The glutamate dehydrogenase pathway played an important role in ammonia assimilation in ammonia-grown cells but was found to play a minor role relative to that of the glutamine synthetase/NADPH-glutamate synthase pathway in nitrogen-fixing cells when the intracellular NH4+ concentration and the low affinity of the enzyme for NH4+ were taken into account. In C. butyricum grown on glucose-salt medium with ammonia or N2 as the nitrogen source, glutamate dehydrogenase activity was undetectable, and the glutamine synthetase/NADH-glutamate synthase pathway was the predominant pathway of ammonia assimilation. Under these growth conditions, C. butyricum also lacked the activity of glucose-6-phosphate dehydrogenase, which catalyzes the regeneration of NADPH from NADP+. However, high activities of glucose-6-phosphate dehydrogenase as well as of NADPH-glutamate dehydrogenase with a Km of 2.8 mM for NH4+ were present in C. butyricum after growth on complex nitrogen and carbon sources. The ammonia-assimilating pathway of N2-fixing C. butyricum, which differs from that of the previously studied Bacillus polymyxa and Bacillus macerans, is discussed in relation to possible effects of the availability of ATP and of NADPH on ammonia-assimilating pathways.
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PMID:Ammonia assimilation pathways in nitrogen-fixing Clostridium kluyverii and Clostridium butyricum. 256 48


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