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)

The four half-transamination reactions [the pyridoxal form of Escherichia coli aspartate aminotransferase (AspAT) with aspartate or glutamate and the pyridoxamine form of the enzyme with oxalacetate or 2-oxoglutarate] were followed in a stopped-flow spectrometer by monitoring the absorbance change at either 333 or 358 nm. The reaction progress curves in all cases gave fits to a monophasic exponential process. Kinetic analyses of these reactions showed that each half-reaction is composed of the following three processes: (1) the rapid binding of an amino acid substrate to the pyridoxal form of the enzyme; (2) the rapid binding of the corresponding keto acid to the pyridoxamine form of the enzyme; (3) the rate-determining interconversion between the two complexes. This mechanism was supported by the findings that the equilibrium constants for half- and overall-transamination reactions and the steady-state kinetic constants (Km and kcat) agreed well with the predicted values on the basis of the above mechanism using pre-steady-state kinetic parameters. The significant primary kinetic isotope effect observed in the reaction with deuterated amino acid suggests that the withdrawal of the alpha-proton of the substrates is rate determining. The pyridoxal form of E. coli AspAT reacted with a variety of amino acids as substrates. The Gibbs free energy difference between the transition state and the unbound state (unbound enzyme plus free substrate), as calculated from the pre-steady-state kinetic parameters, showed a linear relationship with the accessible surface area of amino acid substrate bearing an uncharged side chain.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Pre-steady-state kinetics of Escherichia coli aspartate aminotransferase catalyzed reactions and thermodynamic aspects of its substrate specificity. 220 6

The enzyme aspartate aminotransferase was demonstrated cytochemically in the rat hippocampus 4, 7, and 14 days after unilateral entorhinal cortex lesion. At the light microscopic level the enzyme showed a significant activity decrease in the ipsilateral entorhinal terminal field which was similar at all postlesion times investigated. Non-denervated areas, i.e. the inner one-third of the dentate gyrus molecular layer and the radiatum layer of CA2/3, showed an increase of aminotransferase activities. At the electron microscopic level in the entorhinal terminal field of the control (unoperated) side aspartate aminotransferase was localized preferentially in a great number of boutons, containing the cytoplasmic and mitochondrial isoenzymes. Following entorhinal lesion a significant loss of these positively reacting boutons was seen. Most of the degenerating boutons contained reaction product but a small number was negative for aspartate aminotransferase. From 4 to 14 postlesion days the positively reacting boutons of the non-denervated supragranular zone expanded outward into the denervated area according to the known terminal proliferation of the commissural and associational systems. The remaining denervated entorhinal terminal field was reinnervated predominantly by negatively reacting boutons (probably terminal proliferations of septal afferents) and by a small number of positively reacting boutons (probably terminal proliferations of the crossed temporo-dentate pathway). The presence of cytoplasmic aspartate aminotransferase in the terminals of a well-known glutamatergic system is discussed in relation to the possible importance of this enzyme for the production of releasable glutamate.
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PMID:Glutamate producing aspartate aminotransferase in glutamatergic perforant path terminals of the rat hippocampus. Cytochemical and lesion studies. 222 38

Twenty-four hours after acute administration of cocaine HCl (25 mg/kg, i.p.) to male C57BL/6ByJ mice, there was no hepatotoxicity as measured by plasma aspartate aminotransferase (AST) activity. In contrast, daily administration of cocaine (25 mg/kg, i.p.) for 14 days induced marked hepatotoxicity, as characterized by a greater than 400% increase in plasma AST activity when assayed 24 hr after the last injection. Concomitantly, the liver had increased levels of cysteine, gamma-glutamylcysteine, glutathione, cysteinylglycine, glutamate, methionine, taurine, and aspartate. The effect appeared to be selective for compounds of the glutathione metabolic pathways, because repeated cocaine exposure did not affect other amino acids such as leucine, isoleucine, phenylalanine, serine, and valine. There was a positive correlation between the magnitude of the elevation of cysteine and the extent of liver damage. Daily cocaine administration did not affect striatal or frontal cortex glutathione. A final cocaine challenge (50 mg/kg, i.p.) did not affect either hepatic or cerebral glutathione metabolism. The increase in hepatic cysteine and glutathione upon daily cocaine administration is a potentially important compensatory mechanism against cocaine-induced hepatotoxicity.
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PMID:Differential effects of daily administration of cocaine on hepatic and cerebral glutathione in mice. 224 12

This study tests the importance of amino acid transamination in determining the tolerance of immature hearts to ischemic damage. Amino acid transamination was inhibited metabolically by pretreatment with aminooxyacetic acid. The aminooxyacetic acid dose and duration were determined by incubating in vitro tissue homogenate and showing that an 8 mmol/L AOA dose for 5 minutes blocked 90% of alanine aminotransferase and aspartate aminotransferase activity. Control studies in nonischemic hearts showed that coronary perfusion with aminooxyacetic acid for 5 minutes did not impair myocardial performance. In contrast, pretreatment of immature puppies with aminooxyacetic acid severely impaired recovery after 45 minutes of normothermic global ischemia (30% versus 85% recovery in untreated hearts, p less than 0.05). Biochemical analyses of hearts undergoing ischemia showed aminooxyacetic acid to limit lactate production, impair glutamate utilization, prevent alanine production, and limit succinate accumulation (p less than 0.05). These data suggest that amino acid transamination is an important adaptive process in the immature heart that improves its resistance to ischemic damage.
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PMID:Studies of myocardial protection in the immature heart. II. Evidence for importance of amino acid metabolism in tolerance to ischemia. 224 11

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.
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PMID:A complex effect of arsenite on the formation of alpha-ketoglutarate in rat liver mitochondria. 227 50

We evaluated plasma amino acid (AA) concentrations associated with a histologically defined lesion caused by bile duct ligation (BDL) in developing rats. Nineteen rats that underwent BDL at 14 days of age had marked bile duct proliferation with bridging fibrosis, multifocal lobular necrosis, and minimal polymorphonuclear periportal infiltrate in their livers at sacrifice (11-31 days after ligation). These were compared to two age-matched control groups: 21 nonoperated rats and 22 sham-operated rats; and eight rats with cirrhosis caused by carbon tetrachloride. Signs of liver damage including jaundice, growth failure, bleeding, and ascites were accompanied by elevated bilirubin, ammonia, aspartate aminotransferase (AST), and alkaline phosphatase levels in BDL rats compared to controls. They had higher concentrations of total AAs, phenylalanine, tyrosine, and cyst(c)ine when compared to controls and to CCl4-treated rats. Micronodular cirrhosis was present in CCL4-treated rats with elevated AST and alkaline phosphatase levels. Glutamine and glutamate levels were higher in them than in BDL rats or controls, and branched chain AA levels were lower. These two chronic lesions, one obstructive and one hepatotoxic, both result in fibrotic change, but their metabolic abnormalities as reflected in plasma AA levels are distinct. We found that BDL is an appropriate model with which to study metabolic changes and growth failure due to chronic biliary stasis during its progression to frank cirrhosis.
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PMID:Plasma amino acids in long-term models for obstructive versus toxic liver injury in developing rats. 232 99

The NAD analog 3-acetylpyridine adenine nucleotide (APAD), because of its higher oxidation potential, has proven useful for the direct enzymatic measurement of such compounds as lactate, malate, glutamate, etc., for which the equilibrium with NAD+ as oxidant is unfavorable. An enzymatic cycling method which is capable of increasing the sensitivity of such reactions 10,000-fold or more is described. The APADH produced in the original stoichiometric reaction is used to catalyze a cycling reaction that employs lactate and malate dehydrogenases (EC 1.1.1.27 and EC 1.1.1.37) to generate (from lactate plus oxalacetate) very large quantities of pyruvate and malate. After the cycling step, the malate formed is measured with NAD+ and with malate dehydrogenase, plus aspartate aminotransferase, and oxaloacetate to pull this indicator reaction to completion. The application of this cycling method is illustrated by analysis of malate in the range 1 to 10 pmol.
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PMID:An enzymatic cycling method for 3-acetylpyridine adenine dinucleotide to increase the sensitivity of enzymatic methods which employ this NAD analog. 236 93

The pontine nuclei form the key relay nuclei in the cerebropontocerebellar pathway. Although a great deal of information is available regarding the anatomy of this region, the identity of the neurotransmitter(s) contained in the neurons of the pontine gray are not known. The aim of the present investigation is to utilize immunohistochemical techniques to determine whether glutamate, a putative excitatory transmitter, and the enzymes responsible for its metabolism, are found in pontine neurons. Both glutaminase, an enzyme which converts glutamine to glutamate, and aspartate aminotransferase, an enzyme which is involved in the interconversion between glutamate and aspartate, have been proposed to be markers of neurons which use excitatory amino acids as neurotransmitters. The present study utilizes a monoclonal antibody against carbodiimide-fixed glutamate and polyclonal antisera against glutaminase and aspartate aminotransferase in conjunction with the indirect peroxidase technique or the peroxidase-labeled biotin-avidin procedure to localize glutamatergic neurons in the pontine nuclei of the rat. Numerous neurons in all subdivisions of the pontine nuclei were found to contain carbodiimide-fixed glutamate-like immunoreactivity, glutaminase-like immunoreactivity or aspartate aminotransferase-like immunoreactivity. Horseradish peroxidase was injected into the cerebellum of four rats for use with a combined retrograde transport-immunohistochemical procedure. Double-labeled neurons were observed in all subdivisions of the pontine nuclei, indicating that pontine neurons which contain glutamate-like immunoreactivity project to the cerebellum. Based on the hypothesis that increased levels of glutamate, glutaminase and aspartate aminotransferase reflect a transmitter role for glutamate, the present data raise the possibility that glutamate may be a major neurotransmitter of pontocerebellar fibers.
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PMID:Immunohistochemical localization of glutamate, glutaminase and aspartate aminotransferase in neurons of the pontine nuclei of the rat. 242 96

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

Substitution of a lysyl residue for Arg-386 of Escherichia coli aspartate aminotransferase resulted in an extensive decrease in Vmax values (0.8% with the aspartate-2-oxoglutarate pair and 0.2% with the glutamate-oxalacetate pair, compared with the corresponding values for the wild-type enzyme). Kinetic analysis of the four sets of half-reactions, the pyridoxal form of the enzyme with aspartate or glutamate and the pyridoxamine form with 2-oxoglutarate or oxalacetate, allowed us to define the independent effect of the mutation on the reactivity of each substrate. Decrease in the first order rate constant (kmax) was more pronounced in the reactions with five-carbon substrates (glutamate and 2-oxoglutarate) than in those with four-carbon substrates (aspartate and oxalacetate), while the increase in the apparent dissociation constant (Kd) was greater for four-carbon substrates than for five-carbon substrates. The decrease of overall catalytic efficiency as judged by the values, kmax/Kd, was more pronounced in the reactions with five-carbon substrates than in those with four-carbon substrates. Affinities for substrate analogs such as succinate, glutarate, 2-methylaspartate, and erythro-3-hydroxyaspartate, were also considerably decreased by the mutation of the enzyme. These findings indicate that the side chain of the lysyl residue, although it bears a positive charge similar to that of the arginyl residue, is not structurally adequate for the productive binding of a substrate during catalysis.
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PMID:Substitution of a lysyl residue for arginine 386 of Escherichia coli aspartate aminotransferase. 249 35


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