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)

Conditions for reductive methylation of amine groups in proteins using formaldehyde and cyanoborohydride can be chosen to modify selectively the active site lysyl residue of aspartate aminotransferase among the 19 lysyl residues in each subunit of this protein. Apoenzyme must be treated, under mildly acidic conditions (pH = 6), at a relatively low molar ratio of formaldehyde to protein (40:1); and, upon reduction with sodium cyanoborohydride, 85% of the formaldehyde is incorporated at Lysine 258 and 15% at the amino-terminal alanyl residue. The modified protein, characterized after tryptic hydrolysis, separation of the peptides by high performance liquid chromatography procedures and subsequent amino acid analysis, shows that lysine 258 is preferentially modified as a dimethylated derivative. Modified apoenzyme can accept and tightly bind added coenzyme pyridoxal phosphate, as measured by circular dichroism procedures. The methylated enzyme is essentially catalytically inactive when measured by standard enzymatic assays. On the other hand, addition of the substrate, glutamate, produces the characteristic absorption spectral shifts for conversion of the active site-bound pyridoxal form of the coenzyme (absorbance at 400 nm) to its pyridoxamine form (absorbance at 330 nm). Such a half-transamination-like process occurs as in native enzyme, albeit at several orders of magnitude lower rate. This event takes place even though the characteristic internal holoenzyme Schiff's base between Lys-258 and aldehyde of bound pyridoxal phosphate does not exist in methylated, reconstituted holoenzyme. It is concluded that this chemically transformed enzyme can undergo a half-transamination reaction with conversion of active site-bound coenzyme from a pyridoxal to a pyridoxamine form, even when overall catalytic turnover transamination cannot be detected.
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PMID:Site-specific methylation of a strategic lysyl residue in aspartate aminotransferase. 313 Mar 80

The performance characteristics of the Scandinavian Committee on Enzymes (SCE) methods for the assay of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were determined using six automated enzyme analysers. The reagent formulation did not include pyridoxal phosphate (PLP). An optimal operating mode was defined for each instrument and precision was assessed in greater detail on four instruments. A points rating system was devised to place the instruments in the following order of proficiency: IL Multistat III, LKB-8600, Gilford 3500, ABA 100. In contrast to AST, the ALT activity of patient samples was unstable at -20 degrees C over periods as short as seven days. The performance characteristics of the IFCC methods for assay of AST and ALT activities were determined by using three automated enzyme analyzers in order to assess the effect of PLP upon precision and activity of four quality control sera, and to compare the SCE and IFCC methods. Precision of AST assays did not alter on omission of PLP from the IFCC formulation, while that of ALT assays showed slight deterioration. The decrease in activity on omitting PLP was variable with each instrument. A points-rating system was devised to place the methods in the following order of precision: AST: IFCC (-PLP) 118, IFCC 109, SCE 61; ALT: IFCC 125, IFCC (-PLP) 97, SCE 66. The IFCC methods offer better precision, and the overall change on omitting PLP is minimal.
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PMID:Evaluation of commercially formulated aspartate aminotransferase and alanine aminotransferase activity determinations by the Scandinavian Committee on Enzymes and IFCC methods as modified for use with automated enzyme analysers. 323 38

Serum aspartate aminotransferase (AST) activity was measured by the methods recommended by the Scandinavian Committee on Enzymes (SCE) and by the International Federation of Clinical Chemistry (IFCC) with pyridoxal phosphate (PLP) and without (-PLP) in one laboratory at 37 degrees C with the Abbott ABA-100 and in another at 30 degrees C with the IL Multistat III. Reference ranges were determined on 195 healthy hospital staff. Sera from 102 patients with suspected hepatobiliary disease (HBD) and 104 with suspected myocardial infarction (MI) were assayed at both laboratories by all three methods. Based on the above reference ranges, all assays with each method at both hospitals were abnormal in 59 of 67 cases with HBD and 53 of 55 with MI. In aggregate, all three methods yielded comparable rates of misclassification (20-23). The SCE method gave highest false negatives (18) and lowest false positives (5); the IFCC method gave lowest false negatives (1) and highest false positives (20); intermediate values of 8 false positives and 12 false negatives were given by the IFCC (-PLP) method. Using receiver operating characteristic (ROC) curves, the SCE method was clearly superior at 30 degrees C, and the IFCC (-PLP) method was marginally superior at 37 degrees C. However, when the decision threshold corresponded with a 2.5% false positive rate in the non-HBD, non-MI patients, the SCE method gave the lowest false negatives at both temperatures and, on the basis of the present data, must be considered to be the method of choice for AST activity determinations.
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PMID:The diagnostic accuracy of three recommended methods for serum aspartate aminotransferase assays in patients suspected of myocardial infarction and hepatobiliary diseases. 323 44

The distribution of mitochondrial aspartate aminotransferase (AspATm) in liver cells was studied in rats fed pyridoxine-deficient and control diets. Mitochondrial aminotransferase activity was found mainly in the matrix fraction, with smaller amounts in the outer membranes, intermembrane space and cytosol. The precursor of the enzyme was detected in the liver cytosol of both vitamin B-6--deficient and control rats, and its amount was similar in the two groups. When pyridoxal phosphate was added to the assay system, the ratio of enzyme activity to antigenic activity (E/A) of mitochondrial aspartate aminotransferase in the cytosol of both vitamin B-6--deficient and control rats was about 70% of that in the matrix of control rats. On the other hand, the E/A of the matrix enzyme in deficient rats was 53% of that of controls. From these results we concluded that pyridoxal phosphate is not necessary for translocation of mitochondrial aspartate aminotransferase into mitochondrial matrix and that abnormal molecules of the enzyme may be formed in the matrix of vitamin B-6--deficient rat liver.
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PMID:Abnormal molecules of mitochondrial aspartate aminotransferase in the liver of vitamin B-6--deficient rats may be produced in the mitochondrial matrix. 336 40

Ultraviolet-visible absorption spectra of cytosolic aspartate aminotransferase of pig hearts have been analyzed by resolution with lognormal distribution curves. These have been compared with spectra of reference Schiff bases of pyridoxal 5'-phosphate. Spectra of the free enzyme in two different states of protonation and of complexes with monoanions, dicarboxylates, the substrates L-glutamate, L-aspartate, and L-erythro-3-hydroxyaspartate, and the quasi-substrate 2-methylaspartate have been analyzed. Relative amounts of three tautomeric species have been estimated, as have amounts of various enzyme-substrate intermediates. Bandshape parameters which can be used as a guide to analysis of spectra of other pyridoxal phosphate-dependent enzymes are tabulated. Some formation constants and pKa values, which were evaluated at the same time as the spectra of the complexes, are also reported.
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PMID:Quantitative description of absorption spectra of a pyridoxal phosphate-dependent enzyme using lognormal distribution curves. 343 76

The present work describes the purification from rat heart of the mitochondrial and cytosolic forms of the enzymes of the malate--aspartate shuttle, aspartate aminotransferase (EC 2.6.1.1) and malate dehydrogenase (EC 1.1.1.37), by a single procedure after the preparation of the original crude extract. In 10 purification steps, the four enzymes were obtained electrophoretically pure in yields ranging from 6 to 54% of their respective isoenzyme levels in the crude extract. Apoenzymes were formed from the aminotransferases by reacting them with cysteine sulfinate and dialyzing. Complete reconstitution was obtained after a brief incubation with pyridoxal phosphate. All four enzymes are dimers. The mitochondrial isoenzymes are of slightly lower molecular weight than their respective cytosolic forms. Michaelis constants and maximal velocities were derived by the use of primary and secondary plots. In general, the properties of the enzymes from rat heart are similar to the properties of the enzymes from other animal sources.
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PMID:Purification and properties of the cytosolic and mitochondrial forms of aspartate aminotransferase and malate dehydrogenase from rat heart. 358 Jan 73

The relationship between riboflavin and pyridoxine status was studied in 40 patients with sickle cell disease (SCD) and 12 normal children by measuring activation coefficients of erythrocyte glutathione reductase (EGRAC) and aspartate transaminase (ASTAC). Prevalence of riboflavin deficiency was significantly lower in SCD (42.5%) than in control subjects (83%) and there was less pyridoxine deficiency in SCD (10.3%) than control subjects (54.5%). Aspartate transaminase (AST) activities in SCD patients were double those in control subjects. Pyridoxine status of patients, but not of control subjects, was directly affected by riboflavin status as judged from significant correlations between EGRAC and both AST activity and ASTAC. Poor riboflavin status in patients may be restricting availability of pyridoxal phosphate (PLP) due to combined effects of enhanced PLP requirements and effects of poor riboflavin status on the synthesis of PLP by pyridoxine phosphate oxidase (PPO). PPO activity was no different in the two groups.
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PMID:Dependence of pyridoxine metabolism on riboflavin status in sickle cell patients. 360 73

31P NMR spectra of the cytosolic chicken aspartate aminotransferase have been recorded at 161.7 MHz in the pH range of 5.7 to 8.2. The 31P chemical shift was found to be pH-dependent with a pK of 6.85; difference in the chemical shift at pH 5.7 and 8.2 is only 0.35 ppm. The monoanion-dianion transition of 5'-phosphate group of a model Schiff base of pyridoxal phosphate with 2-aminobutanol in methanol is accompanied by a change in 31P chemical shift of 5.2 ppm. It is inferred that the phosphate group of the protein--bound coenzyme is in dianionic form throughout the investigated pH range; the small pH-dependent change of chemical shift may be due to a protein conformational change that affects O-P-O bond angle. In the presence of the 0.1 M succinate, 31P chemical shift of the enzyme remains constant in the pH range of 5.0 to 8.3.
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PMID:[31P-NMR spectra of aspartate aminotransferase from cytosol of the chicken heart]. 360 76

31P-nuclear magnetic resonance and absorption spectra of cytosolic chicken aspartate aminotransferase (L-aspartate:2-oxoglutarate aminotransferase, EC 2.6.1.1) have been recorded in the pH range from 5 to 8.5. The 31P chemical shift was found to be pH-dependent with a pK of 6.85; the chemical shift change was 0.35 ppm. The pK value found by spectrophotometric titration of the enzyme proved to be about 6.0. The monoanion-dianion transition of the 5'-phosphate group of a model Schiff base of pyridoxal phosphate with 2-aminobutanol in methanol is accompanied by a change in the 31P chemical shift of 5.2 ppm. It is inferred that the phosphate group of the protein-bound coenzyme is in a dianionic form throughout the investigated pH range; the pH-dependence of the 31P chemical shift may be due to a conformational change at the active site. In the presence of 100 mM succinate, 6 mM aminooxyacetate or 25 mM cycloserine, the 31P chemical shift is insensitive to pH variations.
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PMID:Phosphorus-31 nuclear magnetic resonance of aspartate aminotransferase from chicken heart cytosol. 365 77

1. In vitro activation of erythrocyte aspartate aminotransferase (EC 2.6.1.1) activity by pyridoxal phosphate was used to assess vitamin B6 nutritional status in forty Sudanese women taking combined, low-dose oral contraceptives (oestrogen-progestogen; OC) and in thirty healthy, non-pregnant women not taking OC. 2. Fourteen (35%) out of forty OC users showed apparent vitamin B6 deficiency. 3. Side-effects associated with OC were more common among the apparently vitamin-B6-deficient OC users than among OC users and non-OC users not deficient in vitamin B6.
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PMID:The effect of oral contraceptives on the apparent vitamin B6 status in some Sudanese women. 367 17


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