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)

A kinetic model of the glutamate dehydrogenase reaction has been formulated for the reversible reaction including all seven reactants (substrates and cofactors NAD(H) and NADP(H)). The model parameters have been evaluated from published initial-rate data. Analysis of the model at cofactor concentration near to that in the intact mitochondrion has shown that the competition for active sites between cofactors and substrates simultaneously present in mitochondria diminishes the steady-state rate of the reaction by a factor of 10 to 100 as compared to the maximal reaction rate. The model predicts near-equilibrium of the reaction substrates with NAD+/NADH cofactor pair and off-equilibrium with NADP+/NADPH. Substrate cycling with futile transfer of hydrogen from NADP+-system to NAD+-system has been found to account under in vivo conditions for no more than 2% of the maximal glutamate dehydrogenase activity in the mitochondria.
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PMID:Theoretical analysis of the glutamate dehydrogenase kinetics under physiological conditions. 613 73

In mouse pancreatic islets the kinetics of insulin secretion and O2 uptake in response to the non-metabolizable leucine analogue (+/-)-BCH (2-endo- aminonorbornane -2-carboxylic acid) were compared. In addition, the fuel-mobilizing effect of (+/-)-BCH was studied with a mitochondrial fraction from islets. (1) Within 2 min 20 mM-(+/-)-BCH markedly enhanced insulin release or O2 consumption by islets respiring in the absence of exogenous fuels. During prolonged exposure to 20 mM-(+/-)-BCH secretion declined more rapidly than O2 uptake. (2) L-Glutamine (10 mM) prevented the decrease of both insulin release and O2 uptake of islets exposed to 20mM-(+/-)-BCH. During the second phase of insulin release in response to 20 mM-(+/-)-BCH + 10 mM-L-glutamine, kinetics of secretion and respiration correlated closely. (3) Initial peaks were consistently seen in the (+/-)-BCH-induced secretory profiles, but never in the respiratory profiles. (4) In contrast with L-glycerol 3-phosphate, L-malate or pyruvate, L-glutamine or L-glutamate maintained low rates of oxidative phosphorylation in B-cell mitochondria. The effects of L-glutamine or L-glutamate were potentiated severalfold by (+/-)-BCH. (5) The effects of other branched-chain amino acids on oxidative phosphorylation resembled their effects on insulin release, redox state of nicotinamide nucleotides and glutamate dehydrogenase activity. (6) The results support the view that (+/-)-BCH stimulates insulin secretion via a primary enhancement of hydrogen supply to the respiratory chain of B-cell mitochondria.
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PMID:Regulation of insulin secretion by energy metabolism in pancreatic B-cell mitochondria. Studies with a non-metabolizable leucine analogue. 637 87

The enzyme-reduced coenzyme-alpha-ketoglutarate ternary complex is a critical intermediate in the glutamate dehydrogenase-catalyzed reaction. Oxalylglycine, a structural analog of alpha-ketoglutarate which contains an amide carbonyl group in place of a reducible ketone group, is one of the few compounds known to complete with alpha-ketoglutarate itself. In order to examine the role of the ketone group of alpha-ketoglutarate in the ternary complex, we have carried out a calorimetric study of the corresponding oxalylglycine ternary complex, determining the complete delta H, delta G, delta S, and delta Cp profiles and the corresponding interaction parameters for that complex and have compared the various parameters with the corresponding ones previously reported for the alpha-ketoglutarate ternary complex. While the overall delta G values of the two ternary complexes differ only slightly, the enzyme-NADPH-oxalylglycine ternary complex appears to achieve much of its stability from a very tight enzyme-oxalylglycine binary complex with little or no contribution from favorable interactions in the ternary complex, while the alpha-ketoglutarate ternary complex appears to achieve the same stability by a large interaction starting from a very weak enzyme-alpha-ketoglutarate binary complex. Consideration of the enthalpic profiles, however, show that this delta G-derived picture is deceptive. The excess binding energy which stabilizes the oxalylglycine binary is in fact due to hydrogen bonding of the amide group of oxalylglycine to the enzyme; in forming the ternary complex, this hydrogen bonding is lost in favor of forming an oxalylglycine-NADPH interaction, which is very similar to the alpha-ketoglutarate-NADPH interaction which stabilizes the alpha-ketoglutarate ternary complex. We conclude that the alpha-ketoglutarate-NADPH interaction must depend on either hydrogen bonding to or steric hindrance by the ketone group and that the existence of this energetically large interaction cannot be ascribed to imine formation between the keto group and enzyme. These findings also indicate the locus on the reaction coordinate where the reduced coenzyme plays a critical role, a role other than its obvious function as a hydride donor.
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PMID:Thermodynamic interactions in the glutamate dehydrogenase-NADPH-oxalylglycine complex. 670 93

Nicotinamide adenine dinucleotide (NAD) decreases the resistance of cerebral vessels and increases the local (hydrogen clearance) and regional (133Xe clearance) cortical blood flow in intact cats. In cerebral blood flow deficiency the level of ammonia in brain tissue is appreciably increased. Favouring normalization of the deranged cerebral blood flow NAD neutralizes excess ammonia by means of glutamate dehydrogenase activity recovery in the reduction amination reaction. This indicates that NAD influences the neurochemical mechanisms of compensatory regulation of the cerebral blood flow.
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PMID:[Mechanisms of action of NAD in cerebral circulatory insufficiency]. 721 6

The numerous physiological and nutritional factors which influence the concentration of serum calcium are considered. The causes of hypercalcaemia and hypocalcaemia are briefly discussed, with particular reference to the clinical symptoms and pathology. The effect of the acid-base status on the serum-ionized calcium level is stressed. The causes of changes in the serum concentrations of phosphorus and magnesium are briefly reviewed, along with the abnormalities of lactate, pyruvate, and hydrogen ion concentrations. The kidney function tests, blood urea nitrogen, serum creatinine, and the renal clearance tests are discussed, with emphasis placed on correlating their results with the findings from repeated urinalyses. The important physiologic influences and pathological processes which result in changes in the concentrations of these parameters are delineated. The causes of increases in the serum enzymes, alkaline phosphatase, alanine transaminase, asparate transaminase, lactic dehydrogenase, sorbitol dehydrogenase, glutamic dehydrogenase, gamma glutamyl transpeptidase, creatinine phosphokinase, amylase and lipase are discussed. The changes in serum bilirubin concentration and its components are fully described, with emphasis placed on the correlation of the findings with urinalysis data and the complexities resulting from the numerous pathologic conditions causing jaundice. These conditions are listed for each of the domestic animals. The other liver function tests, bromosulphthalein dye retention or excretion, serum uric acid and blood ammonia concentration are briefly considered. All the tests described are very useful, and frequently essential, in aiding the veterinary practitioner to arrive at a diagnosis and prognosis, but they never replace clinical acumen.
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PMID:Correlation of changes in blood chemistry with pathological changes in the animal's body: II Electrolytes, kidney function tests, serum enzymes, and liver function tests. 727 79

It is known that the binding of the reduced coenzyme (NADPH) to bovine liver glutamate dehydrogenase is controlled by the presence of phosphate, acetate, and other anions as well as the pH of the medium. These effectors mediate this binding by lowering the pK (8.5) of an ionizable group on the enzyme, and this pK shift is linked to a high enthalpy E <--> E' transition in the protein. In this study, we have measured enthalpy changes and proton transfer for enzyme-NADPH binding under a variety of combinations of phosphate, acetate, and hydrogen in the pairs acetate-NADPH and H(+)-phosphate, and negative interactions are seen in the pairs H(+)-NADPH, phosphate-NADPH, acetate-phosphate, and H(+)-acetate. We present a general model to account for all of these effects. This model incorporates a newly defined coenzyme binding subsite. The observed phenomena are interpreted in terms of the extent of loading of the specific anion-binding site on the enzyme that regulates the ionization of an enzyme group of pK 8.5. A proton is cooperatively shared with two phosphate groups at this site. Furthermore, we conclude that this cooperative trimolecular binding to the enzyme constitutes an allosteric driving force for the high enthalpy two-state transition observed in the ligand binding reactions of this enzyme.
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PMID:Protein-ligand interactions as a driving force for a high-enthalpy two-state transition in glutamate dehydrogenase: the opposing roles of phosphate and acetate ions. 803 Nov 44

We have previously characterized the thermodynamic relationships which govern the dissociation of NADPH from bovine liver glutamate dehydrogenase and the allosteric control of that mechanically and physiologically important process by a variety of effectors. We have found that the cooperative occupancy of a specific anion binding, while the occupancy of a second allosteric acetate binding site disrupts that anion binding site and opposes those effects (Singh & Fisher, 1994). We report here the results of transient-state studies on the kinetics of the various processes involved in this complex equilibrium. We find that the only intrinsically slow steps are those of NADPH binding and dissociation, that the complex kinetic behavior of the overall system is due solely to very rapid equilibrium binding processes involving phosphate, acetate, and hydrogen ions, and that these ions exert their various effects on the kinetics of the binding process by altering the equilibrium concentrations of the two kinetically significant reactive species, E and E-NADPH. The slow intrinsic rates of NADPH association and dissociation are ascribed to a ligand-induced conformational change involving a major alteration in the degree of closure of the enzyme's active-site cleft.
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PMID:A kinetic mechanism of the allosteric control of enzyme-coenzyme binding: glutamate dehydrogenase-NADPH-phosphate-acetate-hydrogen ion interactions. 806 75

Gram amounts of various 15N-enriched L-amino acids have been synthesized using a coupled enzymatic system. Catalytic amounts of 15N-labeled L-glutamate are generated using (15NH4)2SO4, alpha-ketoglutarate, and glutamate dehydrogenase. The labeled glutamate in turn serves as an amine donor to an appropriate alpha-keto acid using the Escherichia coli branched-chain amino acid aminotransferase, the subcloning and overexpression of which is described. In order to drive the reaction to completion the redox cofactor NADPH is regenerated using a glucose dehydrogenase system. Since the amino-transferase catalyzes exchange of the alpha-hydrogen, carrying out this reaction in 2H2O gives rise to 2-2H,2-15N-labeled amino acids. Deuteration can be readily extended to the beta position as well by preexchanging the alpha-keto acids in basic 2H2O. The isotopically labeled amino acids are recovered in yields of 70-80%.
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PMID:Synthesis of alpha, beta-deuterated 15N amino acids using a coupled glutamate dehydrogenase-branched-chain amino acid aminotransferase system. 823 67

We have solved the structure of the binary complex of the glutamate dehydrogenase from Clostridium symbiosum with glutamate to 1.9 A resolution. In this complex, the glutamate side-chain lies in a pocket on the enzyme surface and a key determinant of the enzymic specificity is an interaction of the substrate gamma-carboxyl group with the amino group of Lys89. In the apo-enzyme, Lys113 from the catalytic domain forms an important hydrogen bond to Asn373, in the NAD(+)-binding domain. On glutamate binding, the side-chain of this lysine undergoes a significant movement in order to optimize its hydrogen bonding to the alpha-carboxyl group of the substrate. Despite this shift, the interaction between Lys113 and Asn373 is maintained by a large-scale conformational change that closes the cleft between the two domains. Modelling studies indicate that in this "closed" conformation the C-4 of the nicotinamide ring and the alpha-carbon atom of the amino acid substrate are poised for efficient hydride transfer. Examination of the structure has led to a proposal for the catalytic activity of the enzyme, which involves Asp165 as a general base, and an enzyme-bound water molecule, hydrogen-bonded to an uncharged lysine residue, Lys125, as an attacking nucleophile in the reaction.
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PMID:Conformational flexibility in glutamate dehydrogenase. Role of water in substrate recognition and catalysis. 826 17

Freeze-substituted rat liver embedded in glycol methacrylate (GMA) has been used to demonstrate the activities of several enzymes. The following enzymes could be detected in GMA-sections by the indicated histochemical procedure(s): 5'-nucleotidase (lead salt, cerium-diaminobenzidine), alkaline phosphatase (indoxyl-tetrazolium salt), catalase (diaminobenzidine), acid phosphatase (diazonium salt), lactate dehydrogenase (tetrazolium salt) and glutamate dehydrogenase (tetrazolium salt). The activities of all these enzymes were dramatically decreased compared with the activities demonstrated in unfixed cryostat sections, with the exception of catalase. The activities of the following enzymes could not be detected in GMA-sections: glucose-6-phosphate dehydrogenase (tetrazolium salt), xanthine oxidoreductase (tetrazolium salt), D-amino acid oxidase (cerium-diaminobenzidine-cobalt-hydrogen peroxide) and glucose-6-phosphatase (cerium-diaminobenzidine). The possible role of restricted penetration of reagents into the resin was studied by measuring cytophotometrically the enzyme activities in GMA-sections of 3 and 6 microns in thickness. For all the enzymes that could be detected, the 6 microns:3 microns ratio varied from 1.4 to 2.7. An eventual retarded penetration of reagents into the resin was investigated by measuring cytophotometrically the amount of final reaction product during incubation for acid phosphatase and glutamate dehydrogenase activities. In both cases linear relationships without a lag phase were found for the specific enzyme activities with incubation time. Chemical denaturation of proteins or masking of active sites in proteins due to embedding in the resin monomer may be considered to be the main cause of decreased enzyme activities.
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PMID:Quantitative aspects of enzyme histochemistry on sections of freeze-substituted glycol methacrylate-embedded rat liver. 827 44


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