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)

Using purified enzymes of human origin and patients' sera, we examined factors influencing the in vitro association of pyridoxal phosphate with aspartate aminotransferase (EC 2.6.1.1). The rate of association was markedly retarded by phosphate buffer in comparison with tris(hydroxymethyl)aminomethane or six other buffers. Pyridoxal phosphate at an incubation concentration of 130 mumol/liter reactivated the entire apoenzyme portion of an apoenzyme/holoenzyme mixture within 5 min in tris(hydroxymethyl)aminomethane; in contrast, less than 20% was associated during 15 min in phosphate. Activity measured in tris(hydroxymethyl)aminomethane-buffer without exogenous pyridoxal phosphate was 4% greater than that in phosphate and was slightly increased by increasing the pH of the assay mixture from 7.5 to 8.0. Aspartate in the incubation medium did not retard the stimulation in tris(hydroxymethyl)aminomethane buffer. While the magnitude of stimulation varied greatly among sera, a consistent mean stimulation of 30% for groups of sera with normal activities was found when asparate at 125 mmol/liter, 2-oxoglutarate at 6.7 mmol/liter and tris(hydroxymethyl)aminomethane at 90 mmol/liter were used, an increase over the 16% with phosphate buffer [Clin. Chem. 19, 92 (1973)]. Absorbance spectra suggest pyridoxal phosphate exists as the Schiff base of tris(hydroxymethyl)aminomethane or aspartate, or both, under conditions of assay incubation (without addition of 2-oxoglutarate). Nonenzymatic catalysis of the reaction by pyridoxal phosphate alone or a formation of a protein/pyridoxal phosphate adduct was discounted with use of a D-asparate substrates.
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PMID:Effects of buffers on aspartate aminotransferase activity and association of the enzyme with pyridoxal phosphate. 24 May 13

The nature of the 500-nm chromophore in pig kidney diamine oxidase was investigated by absorption spectroscopy and fluorescence in the presence of various chelating or carbonyl-specific reagents. From the spectroscopic measurements the following conclusions can be drawn. First, the 500-nm absorption band is not due to copper, the reduction of which is not related to the disappearance of this band. Second, phenylhydrazine and cycloserine give rise, upon reaction with the enzyme, to absorptions very similar to those of a pyridoxal enzyme, aspartate aminotransferase. Third, these enzyme derivatives are unexpectedly non-fluorescent. Copper removal, obtained after prolonged incubation of cycloserine-treated enzyme in the presence of reducing and chelating agents, leads to a fluorescence similar to that of cycloserine-aspartate transminase. It is proposed that copper is coordinated to the postulated pyridoxal phosphate of diamine oxidase through the pyridine nitrogen.
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PMID:On the nature of chromophore in pig kidney diamine oxidase. 40 51

Physiological and pathological factors affecting intracellular red cell vitamin B6 metabolism in normal, anaemic and alcoholic man were studied using a new assay for pyridoxine kinase (PnK) together with saturated and total aspartate aminotransferase (EGOT) activities as indirect indices of intracellular pyridoxal 5-phosphate (PLP) availability. In studies of anaemic states, subjects with iron deficiency anaemia demonstrated elevated levels of both PnK and saturated EGOT, while seven out of 17 subjects with inflammatory anaemia had subnormal PnK but variable saturated EGOT activities. Despite a high incidence of complicating inflammatory disease, alcoholic subjects with or without ring sideroblastic anaemia had elevated levels of both PnK and saturated EGOT. As judged from the saturated EGOT and the ratio unsaturated EGOT/saturated EGOT, intracellular PLP availability was always appropriate to the higher levels of PnK activity.
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PMID:Vitamin B6 metabolism in anaemic and alcoholic man. 42 39

Aspartate aminotransferase activity was measured in plasma, in liver and in heart mitochondrial and cytoplasmic preparations from rats immediately after death and after a post-mortem interval of 15 h. No significant stimulation of activity on addition of pyridoxal 5-phosphate to the assay medium could be demonstrated in any preparations obtained immediately after death. Significant stimulation occurred in both cytoplasmic and mitochondrial preparations of liver and myocardium after a 15-h post-mortem interval, but not in plasma stored for the same period. It appears, therefore, that variations in the intracellular saturation of apoenzyme with coenzyme cannot account for the observed differences in activation of aspartate aminotransferase by pyridoxal 5-phosphate in sera from patients with myocardial infarction and liver disease. Changes in degree of saturation of apoenzyme seem to occur intracellularly after cell death or injury and before release into the circulation.
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PMID:The changes in activation of intracellular aspartate aminotransferase by pyridoxal 5-phosphate after cell death. 63 4

Reaction of 1,2-cyclohexanedione with chicken heart cytosolic aspartate transaminase results in loss of enzyme activity complying to first order kinetics up to 70% inactivation. The inactivation rate is markedly decreased in the presence of alpha-ketoglutarate, glutarate or alpha-methylaspartate. The number of arginine residues modified per subunit was approximately two (in enzyme preparations which retained 30% residual activity). The diketone-modified enzyme nearly completely loses affinity for alpha-methylaspartate and glutarate; in contrast, its ability to bind alpha-alanine and catalyze its transamination half-reaction with the bound coenzyme remains unimpaired. From these data it can be inferred that a functional arginine residue is the cationic binding site for the distal carboxyl group of the substrates. The transaminase apoenzyme was inactivated with cyclohexanedione at the same rate as reconstituted holoenzyme. Measurements of circular dichroism showed that the modified apoenzyme is capable to bind pyridoxal-P. No evidence was obtained for the presence of an arginine residue in the coenzyme binding site.
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PMID:[Study of the role of arginine residues in aspartate transaminase from chicken heart cytosol]. 65 97

The Center for Disease Control (CDC), the New York State Department of Health (NYSDH), the College of American Pathologists, and 23 manufacturers of diagnostic products participated in an interlaboratory study of aspartate aminotransferase (EC 2.6.1.1) methodologies. Six different lyophilized materials were prepared and characterized and then distributed to 293 laboratories for aspartate aminotransferase measurements. The specimens included one human serum; four catalytic concentrations of the cytoplasmic isoenzyme, two purified from human erythrocytes, and two from porcine heart; and one matrix bovine serum albumin (30 g/liter) blank. The purified isoenzymes were prepared in the matrix. We present data on Michaelis parameters (Km and Vmax), Arrhenius plots, activation with pyridoxal 5-phosphate, vial-to-vial variability, and stability on reconstitution. The 281 responses showed that most of the laboratories used NADH-detection methods (91.1%), monitored at 340 nm (79.4%), and reported results in U/liter (89.4%). The percentage of laboratories reporting use of reaction temperatures of 30 and 37 degrees C was evenly divided, i.e., 42.7 and 42%, respectively. Analytical values reported by participating laboratories were categorized by reporting temperature, instrument, and method. Results were most consistent for a selected group of laboratories that supplemented optimized reaction solutions with pyridoxal 5-phosphate.
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PMID:An interlaboratory study of measurement of aspartate aminotransferase activity with use of purified enzyme materials. 65 80

Various systems for estimation of aspartate aminotransferase activity were compare with regard to national and international recommendations. An increase of 1-aspartate concentration from 33 mM/1 to 200 mM/1 and of alpha-ketoglutarate from 6.7 mM/1 to 12 mM/1 elevated the enzymatic activity by 30-40%. Addition of pyridoxal phosphate into reaction mixture caused a decrease in the activation from 33% to 7.3%, respectively. The ratio of activation varied from 9.9% to 53.3% in the optimal test using blood serum from patients and phosphate buffer. Thus, one of requirements on evaluation of maximal aspartate aminotransferase activity and on production of reproducible results is application of optimal concentrations of reagents with addition of pyridoxal phosphate into reaction mixture.
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PMID:[Selection of optimal conditions for measuring aspartate aminotransferase activity]. 66 90

The carbonyl reagent amino-oxyacetate is frequently used in metabolic studies to inhibit individual pyridoxal phosphate enzymes. The reaction of this compound with three such enzymes, aspartate transaminase, 4-aminobutyrate transaminase and dopa (3,4-dihydroxyphenylalanine) decarboxylase, was studied to determine the extent to which the inhibition is reversible and the rates at which it takes place. Reactions were followed by observing changes in the absorption spectra of the bound coenzyme and by measuring loss of enzyme activity. The reactions with aspartate transaminase and aminobutyrate transaminase were not rapidly reversible and had second-order rate constants (21 degrees C) of 400 M-1.s.1 and 1300 M-1.s-1 respectively and all all concentrations studied showed the kinetics of a simple bimolecular reaction. The reaction with 4-aminobutyrate transaminase could not be reversed and that with aspartate transaminase could only be reversed significantly by addition of cysteinesulphinate to convert the enzyme into its pyridoxamine form. The first-order rate constant (21 degrees C) for the reverse reaction was 4 X 10(-5)s-1. Dopa decarboxylase inhibition by amino-oxyacetate was more rapid and more readily reversible, but measurements of rate and equilibrium constants were not obtained for this enzyme.
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PMID:The reaction of amino-oxyacetate with pyridoxal phosphate-dependent enzymes. 66 36

Crystalline complexes of cytoplasmic aspartate aminotransferase of pig heart with the substrates L-glutamate and L-aspartate, and with other amino acids, have been prepared and polarized light absorption spectra have been measured. Striking differences in the directions of polarization of the absorption bands are seen. A complete half-transamination of pyridoxal phosphate to pyridoxamine phosphate by aspartate or by cysteine sulfinate can be demonstrated in the crystal as can the accumulation of a quinonoid intermediate with erythro-beta-hydroxyaspartate. X-ray diffraction studies show that the crystals with erythro-beta-hydroxyaspartate and alpha-methylaspartate are isomorphous with those of both alpha and beta subforms of the native enzyme.
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PMID:Crystalline enzyme.substrate complexes of asparate aminotransferase. 67 Jan 92

1. Diets containing graded levels of pyridoxine hydrochloride (to supply 0.26--30 mg pyridoxine/kg) were given to seven duplicate groups of turbot (Scophthalmus maximus) for 12 weeks and their growth rate was measured during this period. 2. Good growth was obtained on all treatments except those groups given less than 1.0 mg pyridoxine/kg diet. These fish grew normally until weeks 8--10 but thereafter their weight gain was significantly less than that for other treatments. 3. Measurements of aspartate aminotransferase (EC 2.6.1.1) in muscle and liver and of alanine amino-transferase (EC 2.6.1.2) in liver of the turbot showed that the activities of these enzymes increased with increasing dietary pyridoxine intake up to a level of 2.5 mg pyridoxine/kg. The activities of these enzymes were not further enhanced by additional dietary pyridoxine. 4. Percentage stimulation of these enzymes by pre-incubation of extracts with pyridoxal phosphate was minimal with those groups of turbot given 2.5 mg pyridoxine/kg diet or more. 5. It is concluded that the dietary requirement of turbot for vitamin B6 can be safely met with a diet containing between 1.0 and 2.5 mg pyridoxine/kg. 6. An eighth group of turbot given the pyridoxine antagonist 4-deoxypyridoxine hydrochloride (20 mg/kg) showed retarded growth after 2 weeks, together with a high mortality rate.
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PMID:Studies on the nutrition of marine flatfish. The pyridoxine requirement of turbot (Scophthalmus maximus). 69 64


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