Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P17174 (aspartate aminotransferase)
 14,872 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Viable toadfish hepatocytes were separated into distinct subpopulations by gradient centrifugation. Although 3-5 density subpopulations were obtained for each fish, only two metabolically and enzymatically different subpopulations could be discerned. In all cases, hepatocytes with the lowest density (less than 1.040 g ml-1) were more oxidative in scope, as judged by the activities of mitochondrial enzymes (citrate synthase, aspartate aminotransferase, glutamate dehydrogenase); activities of these enzymes (normalised to cell protein) were on average two- to threefold higher than in subpopulations with higher densities. Lower-density hepatocytes also contained higher levels of the urea cycle enzymes arginase and ornithine carbamoyltransferase. The higher-density subpopulations showed no significant differences from each other in enzymatic activities. Compared with lower-density cells, these hepatocytes had higher activities of two cytosolic enzymes, malate dehydrogenase and glutathione-S-transferase. There was no distinct distribution pattern for alanine aminotransferase and glutamine synthetase. Despite generally lower oxidative enzyme content, higher-density hepatocytes were metabolically more active, with 2.5- to fourfold higher rates of urea synthesis, gluconeogenesis and oxidation of lactate. We conclude that, although the toadfish liver shows distinct enzymatic and metabolic heterogeneity, this heterogeneity is dissimilar to the zonation pattern in the livers of mammals, in that separated toadfish hepatocyte types did not appear to possess exclusive metabolic functions. Notably, all cells were capable of metabolic functions that are strictly localised in mammalian liver. In nitrogen metabolism, glutamine synthetase displays a distribution pattern commensurate with its unique metabolic function in the liver of the ureogenic toadfish. Further, all subpopulations possessed detoxification capabilities as indicated by high levels of glutathione-S-transferase, a 'phase II' conjugation enzyme.
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PMID:Metabolic and enzymatic heterogeneity in the liver of the ureogenic teleost Opsanus beta. 205 Nov 31

1. Glutamine was found to be the main carbon and nitrogen product of the metabolism of aspartate in isolated guinea-pig kidney-cortex tubules. Glutamate, ammonia and alanine were only minor products. 2. Carbon-balance calculations and the release of 14CO2 from [U-14C]aspartate indicate that oxidation of the aspartate carbon skeleton occurred. 3. A pathway involving aspartate aminotransferase, glutamate dehydrogenase, glutamine synthetase, phosphoenolpyruvate carboxykinase, pyruvate kinase, pyruvate dehydrogenase and enzymes of the tricarboxylic acid cycle is proposed for the conversion of aspartate into glutamine. 4. Evidence for this pathway was obtained by: (i) inhibiting aspartate removal by amino-oxyacetate, an inhibitor of transaminases, (ii) the use of methionine sulphoximine, an inhibitor of glutamine synthetase, which induced a large increase in ammonia release from aspartate, (iii) the use of quinolinate, an inhibitor of phosphoenolpyruvate carboxykinase, which inhibited glutamine synthesis from aspartate, (iv) the use of alpha-cyano-4-hydroxycinnamate, an inhibitor of the mitochondrial transport of pyruvate, which caused an accumulation of pyruvate from aspartate, and (v) the use of fluoroacetate, an inhibitor of aconitase, which inhibited glutamine synthesis with concomitant accumulation of citrate from aspartate.
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PMID:Glutamine synthesis from aspartate in guinea-pig renal cortex. 236 82

The activities of alanine-, aspartate- and branched-chain amino-acid transaminases, glutamine synthetase, glutamate dehydrogenase and adenylate deaminase in white adipose tissue of adult male rats have been determined in animals submitted to 12-h cold exposure (4 degrees C) or to 24-h food deprivation. Starvation resulted in small changes in glutamate dehydrogenase and alanine transaminase when expressed per unit of protein weight, inducing an increase in branched-chain amino-acid transaminase and glutamine synthetase. Cold exposure showed the same effects as starvation with respect to glutamate dehydrogenase and alanine transaminase, but induced increases in glutamine synthetase and aspartate transaminase. It is concluded that starvation increases the handling of some amino acids by white adipose tissue and the detoxification of the ammonia thus evolved. The changes observed suggest a different pattern of amino-acid metabolism enzyme changes with either cold or starvation.
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PMID:Amino-acid metabolism enzyme activities in rat white adipose tissue. 243 May 32

To contribute to our understanding of nitrogen metabolism in the developing chick we have studied in liver, intestine and yolk sac membrane the ontogeny of both aspartate- and alanine transaminases, glutamate dehydrogenase, adenylate deaminase, glutamine synthetase and xanthine dehydrogenase activities. Liver enzyme activities were much higher than those of the same enzymes in intestine and yolk sac membrane, the latter having the lowest activities. In the liver, both alanine transaminase and glutamate dehydrogenase increased their activity just before hatching, xanthine dehydrogenase and glutamine synthetase develop their highest activity just after hatching, while aspartate transaminase and adenylate deaminase attained the highest levels just with adulthood. From the pattern of enzyme activity in yolk sac membrane and intestine it can be inferred that after hatching, the amino-acid metabolism in these tissues is considerably enhanced, with higher production of ammonia from amino acids, as indicated by the rise in adenylate deaminase, as well as increased potentiality in production of both alanine and glutamine. It can be concluded that hatching coincides with a deep change of pace in amino-acid metabolism in the organs studied fully comparable with that observed in Mammals at the end of lactation, with the difference that the adaptation to the new diet in the case of the chick is much more sudden than weaning is for the rat.
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PMID:Amino-acid metabolism enzyme activities in the liver, intestine and yolk sac membrane of developing domestic fowl. 243 52

An investigation of several neurochemical consequences of exposure of the rat to 3/4 of the estimated single injection LD50 quantity of trimethyltin chloride (TMT) indicated that a significant elevation in the levels of glutamine (Gln) and 5-hydroxyindole acetic acid (5-HIAA) occurred at post-dosing day 7 in each examined region of the brain; elevated Gln persisted in the hippocampus through day 14 and returned to control levels at day 28. At post-dosing day 7, levels of glutamate were decreased in the hippocampus, while levels of GABA were decreased in hippocampus and frontal cortex, but not in corpus striatum; hippocampal glutamate and GABA returned to control levels by post-dosing day 14. Decreased levels of taurine (Tau) occurred on day 7 in both hippocampus and frontal cortex; hippocampal Tau remained below control levels through post-dosing day 28. Levels of other amino acids and of amines and amine metabolites were not altered by TMT in the 7 to 28 day post-dosing interval. At day 7, TMT treatment did not alter brain regional activities of glutamine synthetase; however, plasma ammonia was elevated 100% above the control value. Alterations in several serum enzymes (esp., alkaline phosphatase and aspartate aminotransferase) revealed several other peripheral consequences of TMT exposure which persist through post-dosing day 28. The more prominent and wide-spread neurochemical alterations resulting from TMT exposure appear to reflect consequences of hyperammonemia resulting from a peripheral effect of the organotin compound.
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PMID:Trimethyltin-induced alterations in brain amino acids, amines and amine metabolites: relationship to hyperammonemia. 243 91

The activities of several enzymes involved in the metabolism of aspartate and glutamate were measured in striatal (nucleus caudatus and putamen) homogenates 2-3, 6-7, and 35-40 days following frontoparietal and frontal cortical ablation. The activity of glutamine synthetase (GS) was substantially increased (46-48%) on the operated side 6-7 days following the lesion whereas smaller changes were observed at 2-3 and 35-40 days after lesion. In contrast, decreased levels of glutaminase and malate dehydrogenase (MDH) were observed by 6-7 days while no significant change was found at either 2-3 or 35-40 after the lesion. The activities of glutamate dehydrogenase (GDH) and glutamate decarboxylase (GAD) were elevated after 35-40 days whereas no changes in the levels of either GDH or aspartate aminotransferase (ASAT) were found at 2-3 or 6-7 days after the fronto-parietal decortication. When only the frontal cortex was removed quantitatively similar changes were observed in striatal GS and glutaminase activity. The content of glutamate and glutamine in the denervated striatum followed qualitatively the changes in glutaminase and GS. The results indicate that the degeneration of cortico-striatal terminals causes a profound glial reaction in the striatum, and both glutaminase and MDH are present in relatively high concentrations in the corticostriatal terminals.
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PMID:Effect of cortico-striate pathway lesion on the activities of enzymes involved in synthesis and metabolism of amino acid neurotransmitters in the striatum. 285 84

The short-term metabolic fate of blood-borne [13N]ammonia was determined in the brains of chronically (8- or 14-week portacaval-shunted rats) or acutely (urease-treated) hyperammonemic rats. Using a "freeze-blowing" technique it was shown that the overwhelming route for metabolism of blood-borne [13N]ammonia in normal, chronically hyperammonemic and acutely hyperammonemic rat brain was incorporation into glutamine (amide). However, the rate of turnover of [13N]ammonia to L-[amide-13N]glutamine was slower in the hyperammonemic rat brain than in the normal rat brain. The activities of several enzymes involved in cerebral ammonia and glutamate metabolism were also measured in the brains of 14-week portacaval-shunted rats. The rat brain appears to have little capacity to adapt to chronic hyperammonemia because there were no differences in activity compared with those of weight-matched controls for the following brain enzymes involved in glutamate/ammonia metabolism: glutamine synthetase, glutamate dehydrogenase, aspartate aminotransferase, glutamine transaminase, glutaminase, and glutamate decarboxylase. The present findings are discussed in the context of the known deleterious effects on the CNS of high ammonia levels in a variety of diseases.
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PMID:Cerebral ammonia metabolism in hyperammonemic rats. 285 53

Activity levels of the enzymes of glutamate metabolism were determined in the neuronal perikarya and synaptosomes isolated from the cerebral cortex of normal and hyperammonemic rats. In neuronal perikarya, the activities of glutamate dehydrogenase, aspartate, alanine aminotransferases and glutamine synthetase were elevated in hyperammonemic states. In synaptosomes, glutamate dehydrogenase and aspartate aminotransferase were suppressed, while glutamine synthetase and glutaminase were elevated. These results suggested the involvement of neuronal perikarya in ammonia detoxification at least in acute hyperammonemic states.
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PMID:Differential response of enzymes of glutamate metabolism in neuronal perikarya and synaptosomes in acute hyperammonemia in rat. 286 71

The relationship between nitrogen assimilation, metabolism and aflatoxin formation has been investigated in a toxigenic and a non-toxigenic strain of Aspergillus parasiticus. Ammonia from the medium is mainly assimilated via NADP-requiring glutamate dehydrogenase. During growth NAD-requiring glutamate dehydrogenase followed an inverse pattern of activity with respect to NADP glutamate dehydrogenase. Alpha-ketoglutarate, the product of NAD glutamate dehydrogenase, stimulated acetate incorporation into aflatoxins. Glutamine synthetase, ornithine transcarbamylase, both utilizing glutamate as substrate were assayed under different growth conditions. An important regulatory role for glutamine synthetase is suggested. The metabolic route of asparagine utilization was also investigated. Both the known pathways, glutamate oxaloacetate transaminase and glutamate pyruvate transaminase are operative simultaneously.
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PMID:Nitrogen metabolism in Aspergillus parasiticus NRRL 3240 and A. flavus NRRL 3537 in relation to aflatoxin production. 287 96

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.
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PMID:Short-term metabolic fate of [13N]ammonia in rat liver in vivo. 287 38


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