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

1. Isolated hepatocytes were used to establish the reasons for the accumulation of aspartate, previously observed when the isolated rat liver was perfused with ethanol in the presence of alanine or ammonium lactate. 2. The isolated cells did not form aspartate when incubated with alanine and ethanol, but much aspartate was formed on incubation with ammonium lactate and ethanol. 3. Urea was the main nitrogenous product on incubation with alanine, in contrast with the perfused liver, where major quantities of NH4+ are also formed. When the formation of urea was nullified by the addition of urease, alanine plus ethanol caused aspartate formation, indicating that aspartate formation depends on the presence of critical concentrations of NH4+. 4. The accumulated aspartate was present in the cytosol. Ethanol halved the content of 2-oxoglutarate in the cytosol and more than trebled that of glutamate in the mitochondria. 5. The findings support the assumption that 2-oxoglutarate formed by the mitochondrial aspartate aminotransferase is not translocated to the cytosol in the presence of ethanol and NH4+, because it is rapidly converted into glutamate, the dehydrogenation of ethanol providing the required NADH. Aspartate, however, is translocated to the cytosol and accumulates there because of the lack of stoicheiometric amounts of oxoglutarate.
 ...
PMID:The accumulation of aspartate in the presence of ethanol in rat liver. 120 Oct 7

Feedback control between flux through the phosphorylating electron transport chain and the coordination of flux through individual steps of the citric acid cycle have been investigated under a number of different conditions of substrate availability and workloads in the isolated perfused rat heart. The transition from substrate-free perfusion to perfusion with glucose and insulin with no change of workload was associated with increases in the pool sizes of citric acid cycle intermediates except for oxaloacetate, but with an initial imbalance of flux through individual steps in the cycle and transport of anions of the malate-aspartate cycle across the mitochondrial membrane. Flux through citrate synthase initially increased while that through alpha-ketoglutarate dehydrogenase decreased. Of the components of the malate-aspartate cycle, flux through the malate-alpha-ketoglutarate exchange was increased prior to that through the glutamate-aspartate exchange and intramitochondrial aspartate aminotransferase. These changes can be accounted for on the basis of known kinetic controls of the enzyme and transport steps in response to increased pyruvate, acetyl-CoA, and NADH delivery at an approximately constant rate of ATP turnover.
 ...
PMID:Coordination of citric acid cycle activity with electron transport flux. 126 91

In addition to the normal carboxylation reaction, phosphoenolpyruvate carboxylase from Zea mays catalyzes a HCO3(-)-dependent hydrolysis of phosphoenolpyruvate to pyruvate and Pi. Two independent methods were used to establish this reaction. First, the formation of pyruvate was coupled to lactate dehydrogenase in assay solutions containing high concentrations of L-glutamate and aspartate aminotransferase. Under these conditions, oxalacetic acid produced in the carboxylation reaction was efficiently transaminated, and decarboxylation to form spurious pyruvate was negligible. Second, sequential reduction of oxalacetate and pyruvate was achieved by initially running the reaction in the presence of malate dehydrogenase with NADH in excess over phosphoenolpyruvate. After the reaction was complete, lactate dehydrogenase was added, thus giving a measure of pyruvate concentration. At pH 8.0 in the presence of Mg2+, the rate of phosphoenolpyruvate hydrolysis was 3-7% of the total reaction rate. The hydrolysis reaction catalyzed by phosphoenolpyruvate carboxylase was strongly metal dependent, with rates decreasing in the order Ni2+ greater than Co2+ greater than Mn2+ greater than Mg2+ greater than Ca2+. These results suggest that the active site metal ion binds to the enolate oxygen, thus stabilizing the proposed enolate intermediate. The more stable the enolate, the less reactive it is toward carboxylation and the greater the opportunity for hydrolysis.
 ...
PMID:Hydrolysis of phosphoenolpyruvate catalyzed by phosphoenolpyruvate carboxylase from Zea mays. 163 56

Several key enzymes related to carbohydrate metabolism were assayed in Setaria digitata. In the cytosolic fraction pyruvate kinase, phosphoenolpyruvate carboxykinase, malate dehydrogenase, malic enzyme, aspartate transaminase and alanine transaminase were found. Among the TCA cycle enzymes succinate dehydrogenase, fumarate reductase, fumarase (malate dehydration), malate dehydrogenase (malate oxidation and oxaloacetate reduction) and malic enzyme (malate decarboxylation) were detected in the mitochondrial fraction. Only reduced nicotinamide adenine dinucleotide (NADH) dehydrogenase, NADH oxidase and NADH-cytochrome c reductase were found in the mitochondrial fraction. The significance of these results with respect to the metabolic capabilities of the worm are discussed.
 ...
PMID:Intermediary carbohydrate metabolism in the adult filarial worm Setaria digitata. 177 15

The subcellular localization of NAD- and NADP-linked glutamate dehydrogenases (GDH-NAD and GDH-NADP), alanine aminotransferase (ALAT) and aspartate aminotransferase (ASAT) in epimastigotes of Trypanosoma cruzi was studied by digitonin extraction from whole cells, subcellular fractionation by differential centrifugation and isopycnic ultracentrifugation. All enzymes presented both a cytosolic and a mitochondrial form; in addition, GDH-NADP seems to have a third, still undefined, localization. The results are compatible with the existence of two pathways for the production of L-alanine linked to the reoxidation of glycolytic NADH, one operative in the mitochondrion and the other in the cytosol, and perhaps responsible for the existence of the two alanine pools detected by 13C-nuclear magnetic resonance (B. Frydman et al., Eur. J. Biochem. 192 (1990) 363-368).
 ...
PMID:Subcellular localization of glutamate dehydrogenases and alanine aminotransferase in epimastigotes of Trypanosoma cruzi. 177 28

Sensitive flow-injection analyses of aspartate, glutamate, 2-oxoglutarate, and oxaloacetate were developed. The analytes were enzymatically coupled with NADH which was monitored by light emission from immobilized bacterial bioluminescence enzymes. Aspartate (or oxaloacetate) was assayed on the basis of NADH consumption by introducing the sample through a coimmobilized aspartate aminotransferase-malate dehydrogenase column. The assay responded linearly from 100 pmoles to 5 nmoles per assay. Glutamate (2-oxoglutarate) was determined by formation of NADH in the glutamate dehydrogenase reaction. The measuring range for glutamate was from 10 pmoles to 100 nmoles per assay. The precision of the flow-injection method was generally excellent, and the sensitivities of the described assays were 100-1000-fold higher than with spectrophotometric methods. The immobilized enzyme preparations were stable for several months in storage, and the enzyme columns could be used for 600-800 analyses. Flow-injection analyses of amino acids and related compounds by NADH/bioluminescence-coupled reactions provide a sensitive, fast, and inexpensive assay method for a wide variety of purposes.
 ...
PMID:Flow-injection analysis of amino acids and their metabolites by immobilized vitamin B6-dependent enzymes. Sensitive determination of L-aspartate, L-glutamate, 2-oxoglutarate, and oxaloacetate. 197 15

This investigation presents disturbances of the mitochondrial metabolism by arsenite, a hydrophilic dithiol reagent known as an inhibitor of mitochondrial alpha-keto acid dehydrogenases. Arsenite at concentrations of 0.1-1.0 mM was shown to induce a considerable oxidation of intramitochondrial NADPH, NADH, and glutathione without decreasing the mitochondrial membrane potential. The oxidation of NAD(P)H required the presence of phosphate and was sensitive to ruthenium red, but occurred without the addition of calcium salts. Mitochondrial reactions producing alpha-ketoglutarate from glutamate and isocitrate were modulated by arsenite through various mechanisms: (i) both glutamate transaminations, with oxaloacetate and with pyruvate, were inhibited by accumulating alpha-ketoglutarate; however, at low concentrations of alpha-ketoglutarate the aspartate aminotransferase reaction was stimulated due to the increase of NAD+ content; (ii) the oxidation of isocitrate was stimulated at its low concentration only, due to the oxidation of NADPH and NADH; this oxidation was prevented by concentrations of citrate or isocitrate greater than 1 mM; (iii) the conversion of isocitrate to citrate was suppressed, presumably as a result of the decrease of Mg2+ concentration in mitochondria. Thus the depletion of mitochondrial vicinal thiol groups in hydrophilic domains disturbs the mitochondrial metabolism not only by the inhibition of alpha-keto acid dehydrogenases but also by the oxidation of NAD(P)H and, possibly, by the change in the ion concentrations.
 ...
PMID:A complex effect of arsenite on the formation of alpha-ketoglutarate in rat liver mitochondria. 227 50

Some NADH-linked aspartate aminotransferase (AST) assay systems may produce significant errors due to endogenous pyruvate because the pre-incubation time employed is too short and/or because the reagent lactate dehydrogenase (LD) activity is inadequate. Such errors in patient specimens may go unnoticed if quality control materials themselves contain a low pyruvate concentration. A theory of pyruvate interference in AST assay is formulated and calculation programs are described which will allow a laboratory to assess whether their particular AST methods are likely to be subject to such interference and also to predict a way of removing any error thus identified.
 ...
PMID:The development of computer programs to predict and minimise the effect of sample pyruvate on aspartate aminotransferase assays. 238 59

We have found previously (Fahien, L.A., Kmiotek, E.H., MacDonald, M. J., Fibich, B., and Mandic, M. (1988) J. Biol. Chem. 263, 10687-10697) that glutamate-malate oxidation can be enhanced by cooperative binding of mitochondrial aspartate aminotransferase and malate dehydrogenase to the alpha-ketoglutarate dehydrogenase complex. The present results demonstrate that glutamate dehydrogenase, which forms binary complexes with these enzymes, adds to this ternary complex and thereby increases binding of the other enzymes. Kinetic evidence for direct transfer of alpha-ketoglutarate and NADH, within these complexes, has been obtained by measuring steady-state rates of E2 when most of the substrate or coenzyme is bound to the aminotransferase or glutamate dehydrogenase (E1). Rates significantly greater than those which can be accounted for by the concentration of free ligand, calculated from the measured values of the E1-ligand dissociation constants, require that the E1-ligand complex serve as a substrate for E2 (Srivastava, D. K., and Bernhard, S. A. (1986) Curr. Tops. Cell Regul. 28, 1-68). By this criterion, NADH is transferred directly from glutamate dehydrogenase to malate dehydrogenase and alpha-ketoglutarate is channeled from the aminotransferase to both glutamate dehydrogenase and the alpha-ketoglutarate dehydrogenase complex. Similar evidence indicates that GTP bound to an allosteric site on glutamate dehydrogenase functions as a substrate for succinic thiokinase. The potential physiological advantages to channeling of activators and inhibitors as well as substrates within multienzyme complexes organized around the alpha-ketoglutarate dehydrogenase complex are discussed.
 ...
PMID:Kinetic advantages of hetero-enzyme complexes with glutamate dehydrogenase and the alpha-ketoglutarate dehydrogenase complex. 274 45

Succinate synthesis from exogenous malate, alpha-ketoglutarate, oxaloacetate and L-glutamate in isolated oxygen-deprived rat heart mitochondria was studied using 1H NMR. The highest rate of succinate synthesis was observed during incubation of mitochondria with a mixture of L-glutamate and oxaloacetate. When mitochondria were incubated with [U-13C] glutamate and oxaloacetate the [U-13C] succinate/succinate and aspartate/succinate ratios were equal to 2. This suggests that the succinate produced from [U-13C] alpha-keto-glutarate formed via transamination of [U-13C] glutamate with oxaloacetate by aspartate aminotransferase exceeds twofold that synthesized via oxaloacetate reduction. It may thus be expected that GTP yield in a reaction catalyzed by the succinic thiokinase will be 2 times higher that of ATP production coupled with NADH-dependent fumarate reduction.
 ...
PMID:A 1H NMR study of succinate synthesis from exogenous precursors in oxygen-deprived rat heart mitochondria. 286 22


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