Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.4.1.2 (glutamate dehydrogenase)
 4,380 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The short-term metabolic fate of [13N]ammonia in the livers of adult male, anesthetized rats was determined. Following a bolus injection of tracer quantities of [13N]ammonia into the portal vein, the single pass extraction was approximately 93%, in good agreement with the portal-hepatic vein difference of approximately 90%. High performance liquid chromatographic analysis of deproteinized liver samples indicated that labeled nitrogen is exchanged rapidly among components of: mitochondrial aspartate aminotransferase and glutamate dehydrogenase reactions and cytoplasmic aspartate aminotransferase and alanine aminotransferase reactions (t1/2 for the exchange of label toward equilibrium is on the order of seconds). Comparison of specific activities of glutamate and ammonia suggests that at 5 s most labeled glutamate was mitochondrial, whereas at 60 s approximately 93% was cytosolic; this change is presumably brought about by the combined action of the mitochondrial and cytosolic aspartate aminotransferases and the aspartate carrier of the malate-aspartate shuttle. Specific activity measurements of glutamate, alanine, and aspartate are in accord with the proposal by Williamson et al. (Williamson, D.H., Lopes-Vieira, O., and Walker, B. (1967) Biochem. J. 104, 497-502) that the components of the aspartate aminotransferase reaction are in thermodynamic equilibrium, whereas the components of the alanine aminotransferase reaction are in equilibrium but compartmented in the rat liver. Despite considerable label in citrulline at early time points, no radioactivity (less than or equal to 0.25% of the total) was detected in carbamyl phosphate, suggesting very efficient conversion to citrulline with little free carbamyl phosphate accumulating in the mitochondria. Our data also show that some portal vein-derived ammonia is metabolized to glutamine in the rat liver, but the amount is small (approximately 7% of that metabolized to urea) in part because liver glutamine synthetase is located in a small population of perivenous cells "downstream" from the urea cycle-containing periportal cells. Finally, no tracer evidence could be found for the participation of the purine nucleotide cycle in ammonia production from aspartate. The present work continues to emphasize the usefulness of [13N]ammonia for short-term metabolic studies under truly tracer conditions, particularly when turnover times are on the order of seconds.
 ...
PMID:Short-term metabolic fate of [13N]ammonia in rat liver in vivo. 287 38

Anaesthetized rats were given an i.v. overload of 200 mmoles of ammonium acetate. Plasma ammonium levels were not altered for up to 20 minutes after the end of the infusion. The load of ammonium, however, increased the overall non-protein nitrogen content of circulating plasma, as for the increase in urea and amino acids (alanine, phenylalanine, aspartate + asparagine and glutamate + glutamine). The activities of glutamine synthetase was found increased in liver, muscle and kidney; and glutamate dehydrogenase increased in liver and decreased in muscle and kidney. Adenylate deaminase decreased in all the studied tissues. The fast enzyme and plasma metabolite adaptations to ammonium overload were all in the sense of favoring the incorporation of ammonium into amino acids (later into urea) as well as to avoid their deamination, thus effectively removing the excess ammonium from the bloodstream.
 ...
PMID:Rapid detoxification of infused ammonium by the anesthetized rat. 290 36

(1) Adult postprandial rats were given a continuous, intravenous infusion of 15N-labelled glutamate, alanine, ammonium chloride and glutamine amide for 6 h. The enrichment in the free hepatic pool was measured for ammonia, glutamine amide, urea, aspartate, glutamate and alanine. (2) Glutamine and glutamate supplied significantly more nitrogen to urea than ammonium chloride or alanine. (3) Glutamate was not a significant source of hepatic ammonia, hence in this situation it is not necessary to impute a major role to glutamate dehydrogenase in hepatic ammoniagenesis for urea synthesis. (4) Glutamine and ammonia, mostly of intestinal origin in the postprandial state, were major precursors of hepatic ammonia. (5) The nitrogen of glutamate and alanine moved to urea primarily through aspartic acid.
 ...
PMID:In vivo metabolism of nitrogen precursors for urea synthesis in the postprandial rat. 290 40

Hepatocytes isolated from livers of fed rats were incubated with a mixture of glucose (10 mM), ribose (1.0 mM), acetate (1.25 mM), alanine (3.5 mM), glutamate (2.0 mM), aspartate (2.0 mM), 4-methyl-2-oxovaleric acid (ketoleucine) (3.0 mM), and, in paired flasks, 10 mM-ethanol. One substrate was 14C-radiolabelled in any given incubation. Incorporation of 14C into glucose, glycogen, CO2, lactate, alanine, aspartate, glutamate, acetate, urea, lipid glycerol, fatty acids and the 1- and 2,3,4-positions of ketone bodies was measured after 20 and 40 min of incubation under quasi-steady-state conditions. Data were analysed with the aid of a realistic structural metabolic model. In each of the four conditions examined, there were approx. 77 label incorporation measurements and several measurements of changes in metabolite concentrations. The considerable excess of measurements over the 37 independent flux parameters allowed for a stringent test of the model. A satisfactory fit to these data was obtained for each condition. There were large bidirectional fluxes along the gluconeogenic/glycolytic pathways, with net gluconeogenesis. Rates of ureagenesis, oxygen consumption and ketogenesis were high under all four conditions studied. Oxygen utilization was accurately predicted by three of the four models. There was complete equilibration between mitochondrial and cytosolic pools of acetate and of CO2, but for several of the metabolic conditions, two incompletely equilibrated pools of mitochondrial acetyl-CoA and oxaloacetate were required. Ketoleucine was utilized at a rate comparable to that reported by others in perfused liver and entered the mitochondrial pool of acetyl-CoA directly associated with ketone body formation. Ethanol, which was metabolized at rates comparable to those in vivo, caused relatively few changes in overall flux patterns. Several effects related to the increased NADH/NAD+ ratio were observed. Pyruvate dehydrogenase was completely inhibited and the ratio of acetoacetate to 3-hydroxybutyrate was decreased; flux through glutamate dehydrogenase, the citric acid cycle, and ketoleucine dehydrogenase were, however, only slightly inhibited. Net production of ATP occurred in all conditions studied and was increased by ethanol. Futile cycling was quantified at the glucose/glucose 6-phosphate, glycogen/glucose 6-phosphate, fructose 6-phosphate/fructose 1,6-bis-phosphate, and phosphoenolpyruvate/pyruvate/oxaloacetate substrate cycles. Cycling at these four loci consumed about 22% of cellular ATP production in control hepatocytes and 14% in ethanol-treated cells.
 ...
PMID:Quantitative analysis of intermediary metabolism in rat hepatocytes incubated in the presence and absence of ethanol with a substrate mixture including ketoleucine. 293 May 1

This study provides explanation for conflicting evidence in the literature relating to changes in mitochondrial function and metabolic parameters during chemically induced diabetes. Diabetes of 3 days' duration (early ketosis) did not alter heart, kidney, or liver mitochondrial respiratory rates with glutamate or succinate even though serum glucose and triglycerides were elevated. Diabetes of 5 weeks' duration did not alter kidney or liver mitochondrial function in the fed adult rat although weight gain was depressed. The amount of kidney mitochondrial protein isolated per gram of tissue was increased by 30% in the diabetic. This increase was reversed by insulin treatment as were the other biochemical modalities measured. Superimposition of a 24-hr fast resulted in enhanced gluconeogenesis as measured by an animal weight loss of 17% within 24 hr (liver weight loss, 21%) and an elevation of serum urea nitrogen by 180% compared to fasted control. Respiratory rates of diabetic kidney mitochondria with glutamate were unaffected in the fasted animal whereas diabetic liver mitochondrial respiratory rates during succinate oxidation were reduced by 43%. Respiratory control was unchanged in the fasted diabetic rat. All the observed changes were reversed by insulin. Variation in the serum and liver metabolic indices (urea nitrogen, creatinine, glycerol, free fatty acids, free amino acids, triglycerides, and glucose) and liver mitochondrial responses to 7 weeks of chemically induced diabetes was affected by the rat strain, Sprague-Dawley versus Sherman, and rat weight, 72 g versus 222 g. Liver mitochondrial respirations in fed Sherman rats were not depressed by diabetes. Both rat strains had elevated liver free fatty acids and glutamate dehydrogenase activity in the diabetic state. Serum leucine, isoleucine, and valine were more elevated and serum lysine and arginine were more depressed in the diabetic Sprague-Dawley rat than in the Sherman rat. Conjectures on these results are presented in the text.
 ...
PMID:Metabolic and mitochondrial disturbances in streptozotocin-treated Sprague-Dawley and Sherman rats. 293 62

Lysine-ketoglutarate reductase was purified 675-fold from bovine liver mitochondria. Product inhibition studies gave results similar to those reported for this enzyme extracted from other sources. Inhibition studies with L-citrulline exhibited mixed inhibition patterns. No inhibition of the partially-purified enzyme by ammonium salts was detected; in contrast, marked inhibition of the enzyme by ammonium was apparently observed in crude liver homogenates. This was probably due to depletion of NADPH and/or 2-oxoglutarate in the assay mixture as a result of conversion of ammonium to glutamate by glutamate dehydrogenase. A similar explanation could account for the high levels of lysine observed in humans with urea cycle disorders.
 ...
PMID:Inhibition of bovine liver lysine-ketoglutarate reductase by urea cycle metabolites and saccharopine. 313 24

The urease enzyme of Campylobacter pylori was studied and compared with that of a related spiral-shaped bacterium, St1, isolated from the rodent ileum. Both bacteria possessed constitutive urease enzymes with activities up to 20-70 times that of Proteus vulgaris. This activity was retained on SDS-polyacrylamide gels. A major catalytic subunit of mol. wt 300,000 was located for all (six) strains of C. pylori subjected to SDS-PAGE whereas St1 had two active forms of mol. wts 140,000 and 150,000. Western-blot analysis indicated the presence of anti-urease antibodies in the sera of patients with C. pylori-associated gastritis. The response to C. pylori urease was not strain-specific but no cross-reactivity was detected between the C. pylori enzyme and that of St1. The very high urease activity of these bacteria is likely to be important in colonisation of the host. Possession of glutamate dehydrogenase activity by both organisms suggests that one role of the urease may be to assimilate the available urea nitrogen. Modification of the local environment to facilitate long-term colonisation is another possible function. Protection from acid is unlikely to be a primary role as the natural habitat of the organism St1 is the non-acid-secreting tissue of the small intestine.
 ...
PMID:The urease enzymes of Campylobacter pylori and a related bacterium. 317 69

A flow injection chemiluminometric assay for urea has been developed based on a minicolumn bioreactor packed with immobilized enzyme-bearing glass beads. The reactor contains immobilized urease, L-glutamate dehydrogenase and L-glutamate oxidase, aligned in this order (upstream to the downstream). When the sample is introduced into the bioreactor, urea is first hydrolysed by urease to produce ammonia, which is then converted into L-glutamate by L-glutamate dehydrogenase. L-Glutamate is finally oxidized by L-glutamate oxidase to produce hydrogen peroxide, which is quantified by measuring chemiluminescence emitted upon admixing with luminol and potassium ferricyanide. One assay cycle is completed within 1 minute. The method is sensitive (detection limit 0.5 nmol) and is linear in the range 0-30 mmol/l. It can be readily applied to the determination of urea in human serum, and requires no blank corrections for ammonia and/or L-glutamate present in serum samples.
 ...
PMID:A chemiluminometric method for the determination of urea in serum using a three-enzyme bioreactor. 321 92

The urea-induced inactivation and dissociation of catalytically active hexamer of glutamate dehydrogenase (L-glutamate-NAD(P)-oxidoreductase, EC 1.4.1.3) from bovine liver were studied using radioactive phosphopyridoxyl derivative of the enzyme immobilized on cyanogen bromide-activated Sepharose CL-4B. It is shown that at neutral pH (7.0-7.8) urea causes dissociation of glutamate dehydrogenase to directly yield catalytically inactive immobilized monomers rather than hexamer's stable fragments at the same time. At pH 8.9 or 5.6 the urea-induced is accompanied by the formation of conformationally stable immobilized dimers or trimers, respectively. The trimers are catalytically active, whereas the dimers did not exhibit any enzymatic activity. The data obtained led to suggestion that the hexamer consists of three either equivalent dimers (3 alpha 2) or of two equivalent trimers (2 alpha 3).
 ...
PMID:[Structural organization of glutamate dehydrogenase. 2. Inactivation and dissociation of immobilized hexamer induced by urea]. 324 Mar 26

The effect of ammonia on the alanine metabolism was investigated in perfused rat liver. Gluconeogenesis was found to be stimulated by physiological concentrations of ammonia, while being inhibited at higher concentrations (5-10 mM). The stimulating effect of 0.5 mM ammonia was studied in greater detail. In addition to glucose formation seen enhanced five times, increased rates were observed for ureogenesis as well as the formation of lactate and pyruvate, demonstrating also activation of the total alanine turnover. Furthermore, the mitochondrial and cytosolic NAD systems were increasingly oxidized as reflected by the beta-hydroxybutyrate/acetoacetate and lactate/pyruvate ratios. The shift of the beta-hydroxybutyrate/acetoacetate ratio was correlated to the ATP demand by gluconeogenesis and ureogenesis. The elevated concentration of pyruvate was found to have caused stimulation of gluconeogenesis since there existed a Michaelis-Menten type relation between pyruvate concentration and glucose formation irrespective of the presence or absence of ammonia. The flux through glutamate dehydrogenase was calculated from the total alanine turnover and urea formation, and noted to be diminished in the presence of ammonia despite the increased alanine turnover. It is concluded that glutamate dehydrogenase, at least in part, controls the total alanine turnover in the absence of ammonia.
 ...
PMID:Stimulation of alanine metabolism in rat liver by ammonia. 325 56


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>