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PubMed2003

Cloning, structural analysis and expression of the gene encoding aspartate aminotransferase from the thermophilic cyanobacterium Phormidium lapideum.

The aspartate aminotransferase gene from the thermophilic cyanobacterium Phormidium lapideum was cloned and expressed in Escherichia coli. The ORF of 1167 nucleotides encodes a protein of 388 amino acids having a molecular weight of 42,099. A molecular model of PIAspAT shows structural features similar to those of the Thermus thermophilus AspAT.

Journal Article↗
PubMed2004

An optimized method for the assay of the red blood cell--age-related enzyme aspartate aminotransferase.

Three methods of preparation of red blood cell concentrate for erythrocyte aspartate aminotransferase measurement were compared: (1) filtration of whole blood through a cellulose column (n = 36); (2) washing of whole blood and aspiration of buffy coat after centrifugation (n = 48); (3) optimized method with washing without aspiration of buffy coat (n = 229).

Aspartate Aminotransferases↗
PubMed1989

Aspartate aminotransferase isoenzymes in Leptosphaeria michotii. Properties and intracellular location.

Two forms of aspartate aminotransferase were obtained from the fungus Leptosphaeria michotii and purified to a state of apparent homogeneity by a five-step purification procedure ending with blue Ultrogel chromatography. Holoenzyme specific activities were 13430 and 9110 nkat oxalacetate/mg protein-1 and isoelectric points were 7.1 and 7.0 for forms A and B, respectively. Both isoenzymes were isologous dimers of Mr 92,000. They differed mainly in their Km for 2-oxoglutarate and aspartate, their ability to use cysteine sulfinate as a substrate and their ability in vitro to be specifically tightly associated as follows: form A with a malate dehydrogenase monomer of Mr 25,000; form B with an unidentified protein of Mr 40,000-44,000. Rabbit antiserum raised against the form A holoenzyme was not reactive against the form B holoenzyme and vice versa. Association of the holoenzyme with the complex essentially provoked a shift of the isoelectric point to 5.8 for form B [corrected] and to 5.2 for form B, without affecting kinetic parameters. In order to localize in situ the two transaminase forms, ultrastructural detection was carried out by immunogold staining of thin sections of Lowicryl-K4M-embedded colonies. Antiserum against form A essentially labelled cytoplasm and cell wall and, to some extent, mitochondria, while antiserum against form B heavily labelled mitochondria and cell wall and to a lesser extent cytoplasm. Moreover, mitochondria were isolated and purified by Percoll-density-gradient centrifugation. Only form A was identified in this subcellular fraction using ELISA.

Ascomycota↗
PubMed1966

Amino acid composition and terminal residues of aspartate aminotransferase from ox heart.

1. The amino acid composition of highly purified aspartate aminotransferase from ox heart was determined. 2. Alanine is the only N-terminal residue. 3. Leucine was identified as the only C-terminal residue. 4. No disulphide bridges are present in the enzyme molecule. 5. The thiol groups are not equally accessible, the accessibility being comparatively easier in the apoenzyme molecule.

Amino Acids↗
PubMed1985

Concomitant purification of three porcine heart mitochondrial enzymes: citrate synthase, aspartate aminotransferase, and malate dehydrogenase.

The mitochondrial enzymes citrate synthase, malate dehydrogenase, and aspartate aminotransferase were purified to homogeneity from porcine hearts by use of Bio-Rex 70, carboxymethylcellulose CM32, and Affi-Gel blue chromatography. This procedure provides relatively rapid, large-scale preparation of the three enzymes based on their differential binding to commercially available cation-exchange resins followed by a final affinity chromatography step.

Ammonium Sulfate↗
PubMed1978

A new cause of increased serum aspartate aminotransferase activity.

Two healthy young women had an unexplained persistent elevation of aspartate aminotransferase (ASAT) activity. In both cases electrophoresis of serum ASAT isoenzymes displayed an abnormally moving fraction that comprised the whole serum activity, while liver and muscle revealed the normal cytoplasmic and mitochondrial isoenzymes. In the first case serum ASAT was found to be bound by serum IgG, in the second case the binding protein remained unidentified.

Adult↗
PubMed1982

Influence of pyridoxal-5'-phosphate on temperature relationship of aspartate aminotransferase and alanine aminotransferase.

The influence of pyridoxal-5'-phosphate on the temperature relationship of aspartate aminotransferase and alanine aminotransferase has been determined. On varying the reaction temperature from 25 degrees to 45 degrees both enzymes showed small but significant deviations from a linear Arrhenius relationship. Supplementation with pyridoxal-5'-phosphate in general enhanced the catalytic activity to the same degree over the entire temperature range. Our results corroborate the findings of Rej but not those of Jung et al.

Alanine Transaminase↗
PubMed1988

Aspartate aminotransferase and alanine aminotransferase serum activities in neonatal transient myocardial ischemia.

The behavior of serum aspartate aminotransferase and alanine aminotransferase was evaluated during the first 30 postnatal days in 16 neonates with clinical, electrocardiographic and echocardiographic features of transient myocardial ischemia. These common laboratory tests, requested usually as an aid to diagnosis and surveillance of myocardial damage both in the adult and infant age groups, do not seem to have any value in the perinatal period compared to established reference values of healthy or asphyxiated controls.

Alanine Transaminase↗
PubMed1987

A kinetic method for quantification of aspartate aminotransferase isoenzymes.

A spectrophotometric assay is proposed to determine the levels of aspartate aminotransferase (AAT) isoenzymes from chicken liver by a steady-state kinetic method which depends on the differential inhibition of these isoenzyme forms by high concentrations of substrate 2-oxoglutarate at pH 6.2. The use of a standard curve permits the determination of the percentage of chicken liver c-AAT and m-AAT isoenzymes. This method yields results in good correlation with those achieved by different extent adipate inhibition and by differential centrifugation.

Animals↗
PubMed1992

Coenzyme binding of a folding intermediate of aspartate aminotransferase detected by HPLC fluorescence measurements.

Equilibrium dissociation and unfolding of dimeric aspartate aminotransferase from Escherichia coli proceeds via two compact monomeric intermediates which have similar hydrodynamic volumes but different fluorescence properties. We probed binding of the coenzyme pyridoxal 5'-phosphate to these intermediates by coupling fluorescence detection to size-exclusion HPLC. This procedure gave additionally an internal conformational probe of the unfolding transitions of the enzyme. It was shown that the first intermediate, M, is able to bind the coenzyme, whereas the second intermediate, M*, is not. It is likely that M is the correctly folded monomer of the protein.

Aspartate Aminotransferases↗
PubMed1986

Plasma clearance of mitochondrial aspartate aminotransferase in the rat: competition with mitochondrial malate dehydrogenase.

In previous experiments we have shown that the rapid clearance in rats of alcohol dehydrogenase, lactate dehydrogenase M4, and the mitochondrial and cytosolic isoenzymes of malate dehydrogenase is largely due to endocytosis by macrophages in liver, spleen and bone marrow. Competition experiments indicated that the dehydrogenases as well as adenylate kinase and creatine kinase MM are endocytosed via the same receptor. We suggested that this receptor contains a group with affinity for the nucleotide-binding sites of the enzymes. We now demonstrate that competition also occurs between mitochondrial malate dehydrogenase and mitochondrial aspartate aminotransferase, which does not require a nucleotide for its activity. At low doses, mitochondrial aspartate aminotransferase was cleared following first-order kinetics (half-life: 19 min). Simultaneous injection of a high dose of mitochondrial malate dehydrogenase strongly retarded the clearance of the aminotransferase. These results make unlikely the hypothesis that a nucleotide-binding site is involved in recognition of enzymes by macrophages.

Animals↗
PubMed1992

AAT1, a gene encoding a mitochondrial aspartate aminotransferase in Saccharomyces cerevisiae.

We have isolated a gene, AAT1, encoding an aspartate aminotransferase (AspAT) from a Saccharomyces cerevisiae genomic library. AAT1 encodes a 451 amino acid protein with a predicted molecular weight of 51,687, which is likely to be the yeast mitochondrial AspAT. Sequence comparison of this yeast AspAT with AspATs from other organisms shows a high degree of homology in regions previously shown to be important for catalysis. However, the yeast mitochondrial AspAT contains four obvious insertions with respect to all other known AspATs, suggesting that the AAT1-encoded protein represents a distinct AspAT.

Amino Acid Sequence↗
PubMed1981

Studies on the influence of combustion exhaust gases and the products of their reaction with ammonia on the living organism. II. The influence on aspartate aminotransferase (AspAT) and alanine aminotransferase (AiAt) activities in the liver of guinea pig.

The behaviour of aspartate aminotransferase (AspAT) an alanine aminotransferase (AIAT) in the whole homogenate and subcellular liver fractions of guinea pigs exposed to combustion exhaust gases and the neutralization products of these gases is presented in this paper. In the liver of animals exposed to the chronic action of combustion exhaust gases a decrease of both enzyme activities in the whole homogenate as well as in the subcellular fractions could be noted. Statistically significant changes are shown by AspAT. In the group of animals subjected to the action of neutralization products an increase of AIAT activity was observed. The activity of AspAT still shows a decrease, but less distinct in comparison with group I. An exception here is the mitochondrial fraction in which the AspAT activity is distinctly increased.

Alanine Transaminase↗
PubMed1982

Covalently modified peptides isolated from aspartate aminotransferase after reaction with pyridoxal 5'-sulfate.

The apoenzyme form of cytosolic aspartate aminotransferase of pig hearts was allowed to react at room temperature with 1 equiv of pyridoxal 5'-sulfate. The resulting covalently modified enzyme was degraded with pepsin. Fluorescent tri-, tetra-, and hexapeptides were isolated and characterized as fragments of the active site sequence: Phe-Ser-Lys-Asn-Phe-Gly-Leu. This sequence contains a modified form (Lys) of lysine-258 that is known to form a Schiff base with pyridoxal phosphate in the active site. The peptides were further degraded by acid hydrolysis to give a fluorescent derivative of lysine with light absorption and chemical properties similar to those of the original modified enzyme. A related series of peptides were obtained from apoenzyme after reaction with the 5-carboxyethenyl analogue of pyridoxal 5'-phosphate.

Amino Acids↗
PubMed1984

Enzyme immunoassay of human cytosolic aspartate aminotransferase.

A sensitive and specific sandwich enzyme immunoassay (EIA) for human cytosolic aspartate aminotransferase (c-AST) has been developed. Serum was incubated with anti-c-AST antibody-coated polystyrene beads, and further incubated with anti-c-AST antibody-peroxidase conjugate. The peroxidase activity bound to the polystyrene bead was proportional to the amount of c-AST. The method allows measurement of serum c-AST ranging from 50-2,000 micrograms/l. No cross-reactivity with m-AST or other serum components was observed. Recovery, within-day precision, and day-to-day precision were good. The levels of c-AST obtained by the proposed EIA were compared with those based on enzyme activity. The results suggest that there is a considerable excess of immunologically active but catalytically inactive c-AST in normal and patient's sera, and that variable specific activities of c-AST are may be found in sera from different individuals.

Antibody Specificity↗
PubMed1990

Aging and vitamin B-6 depletion: effects on plasma pyridoxal-5'-phosphate and erythrocyte aspartate aminotransferase activity coefficients in rats.

Plasma pyridoxal-5'-phosphate (PLP) and erythrocyte aspartate aminotransferase activity coefficients were longitudinally determined in rats. Blood was obtained at weeks 0, 1, 2, 4, 6, 9, and 11 from rats initially aged 3 wk, 3 mo, 12 mo, and 23 mo (weeks 0, 1, 4, 6, and 9 only). The diet groups were ad libitum control (ALC), deficient (DEF), and pair-fed control (PF). Plasma PLP concentrations of controls were highest at 3 mo, intermediate at 3 wk and 12 mo, and lowest at 23 mo. When an additional group of 22-mo-old rats was fed a high-vitamin B-6 diet for 4 wk, their low baseline plasma PLP concentrations did not increase significantly. Plasma PLP decreased significantly within 1 wk and activity coefficients increased significantly by week 4 in all DEF rats. Depletion was most rapid and severe in the youngest DEF rats and least in 12-mo-old DEF rats. Mechanisms for the low plasma PLP control values and resistance to depletion in aged rats remain to be determined.

Aging↗
PubMed1982

Observations on the isoenzymes of aspartate aminotransferase in equine tissues and serum.

The distribution of the isoenzymes of aspartate aminotransferase (AST, E.C. 2.6.1.1.) in equine tissues has been studied to ascertain whether the organ of origin may be identified when the total AST activity of serum is raised. Most tissues contain 3 isoenzymes of cytoplasmic origin (cAST) with isoelectric points of 5.6, 5.7 and 5.9, and one isoenzyme of mitochondrial (mAST) origin with an isoelectric point of 9. Serum from horses with azoturia contained an additional cytoplasmic subform with an isoelectric point of 5.8. This form could not be generated by ageing, freezing and thawing or binding of the enzyme to gamma globulins or lipids. The ratio of cAST to mAST when separated by ion exchange chromatography varies widely between tissues, with no cAST detection in lung and no mAST detection in serum. Ageing of equine muscle homogenates caused the formation of 2 artefactual subforms with isoelectric points of 6.0 and 6.1. It is concluded that, although the ratio of mitochondrial to cytoplasmic AST varies between tissues, there is no tissue specificity of either cytoplasmic or mitochondrial isoenzymes and examination of serum would not indicate the source.

Animals↗