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PubMed1984

Coenzyme active site occupancy as an indicator of independence of the subunits of mitochondrial aspartate aminotransferase.

The enzyme, aspartate aminotransferase, is a dimer consisting of two identical subunits which contain overlapping subunit regions ( Eichele , G., Ford, G.C., Glor , M., Jansonius , J.N., Mavrides , C., and Christen , P. (1979) J. Mol. Biol. 133, 161-180), suggesting the possibility of subunit interactions. The structurally similar cytosolic isozyme exhibits noncooperative binding of pyridoxal 5'-phosphate ( Boettcher , M., and Martinez -Carrion, M. (1975) Biochemistry 14, 4528-4531; Relimpio , A., Iriarte , A., Chlebowski , J.F., and Martinez -Carrion, M. (1981) J. Biol. Chem. 256, 4478-4488) in which the apoenzyme/holoenzyme hybrid dimer shows a distinctive thermal stability. Using a nonequilibrium isoelectric focusing technique, it can be shown that mitochondrial aspartate aminotransferase also binds cofactor in a noncooperative random fashion. However, differential scanning calorimetry (DSC) thermograms show different characteristics from the cytosolic form. These differences are interpreted in terms of unique subunit interactions in this isozyme. Heating to the various DSC transition temperatures shows that the anomalous DSC thermograms in partially coenzyme-saturated apoenzyme preparations are due to a selective dissociation of apoenzyme subunits into monomers which are irreversibly denatured. The remaining holoenzyme monomers reassociate and form stable holoenzyme dimers. The net result is retention of the initial concentration of holoenzyme subunits present in any given mixture. Random occupancy of active sites and similar electrophoretic and DSC patterns upon heating of partially saturated apoenzyme preparations is observed whether the coenzyme, pyridoxal phosphate or pyridoxamine phosphate alone, or borohydride-reduced Schiff's bases of coenzyme-substrate analogue derivatives are used as active site directed ligands. The latter resemble covalent enzyme-substrate intermediates.

Animals↗

PubMed1980

An immunochemical procedure for determination of mitochondrial aspartate aminotransferase in human serum.

An immunochemical procedure is described for quantitation of mitochondrial aspartate aminotransferase (m-AspAT; EC 2.6.1.1) activity in human serum specimens. Antibodies directed against purified soluble aspartate aminotransferase (s-AspAT) from human erythrocytes were produced in rabbits and partly purified. Antibody sufficient for analyses of > 6000 specimens could be obtained from 15 mL of rabbit antiserum; contaminant AspAT activity of the antibody preparation was < 0.4 U/L. Addition of antibody directly to purified AspAT isoenzymes resulted in inhibition of s-AspAT but had no measurable effect upon m-AspAT. Antibody is incubated with serum in the presence of polyethylene glycol for 60 min at room temperature, then 60 min at 4 degrees C, and centrifuged (7000 x g, 4 degrees C, 15 min). No detectable s-AspAT activity remains in the supernatant fluid; thus m-AspAT activity can be measured directly. Precision, both within-day and day-to-day, was < 1 U/L, or 3.0% of residual m-AspAT activity. The method completely removed 1200 U of purified s-AspAT activity per liter; addition of s-AspAT to serum in increasing concentrations of about 500 U/L had no effect upon the measurement of residual m-AspAT activity. Results of the procedure described showed excellent correlation with those by an alternative procedure involving antibodies directed against m-AspAT. Addition of both anti-s- and anti-m-AspAT antibodies resulted in complete removal of serum AspAT activity. Univalent Fab fragments prepared anti-s-AspAT antibodies were capable of directly inhibiting s-AspAT activity without precipitation. Although a homogeneous immunoinhibition assay was possible, the greater precision of the precipitation assay made it preferable.

Animals↗

PubMed1982

Chemical modification of a functional arginyl residue (Arg 292) of mitochondrial aspartate aminotransferase. Identification as the binding site for the distal carboxylate group of the substrate.

Mitochondrial aspartate aminotransferase is inactivated by dicarbonyl reagents selectively modifying arginyl residues. Treatment with phenylglyoxal inactivates the enzyme with concomitant modification of 2.7 mol of arginyl residues/mol of subunit. If the reaction is performed in the presence of the transaminating substrate pair aspartate/oxalacetate, only 1.3 mol of arginyl residues/mol of subunit are labeled and the enzymic activity remains at 75% of the original value. One particular residue, identified by peptide analysis as Arg 292, is completely protected against modification in the presence of the substrate pair, indicating a role of its guanidinium group in substrate binding. On the basis of x-ray crystallographic studies of the complex of apoenzyme with N-(5'-phosphopyridoxyl)-aspartate (minus pyridoxal form of the enzyme), Arg 292 has been proposed as the binding site of the distal carboxylate group (Ford, G. C., Eichele, G., and Jansonius, J. N. (1980) Proc. Natl. Acad. Sci. U. S. A. 77, 2559-2563). The enzyme with blocked Arg 292 is not completely inactive, and its molecular activity toward dicarboxylic substrates is of the same order of magnitude as that of the native enzyme toward alanine, which is 10(5) times lower than that toward dicarboxylic substrates. The activity toward alanine is unchanged but the rate-enhancing effect of formate on the transamination of alanine is impaired. Formate is assumed to occupy the binding site of the distal carboxylate group (Morino, Y., Osman, A. M., and Okamoto, M. (1974) J. Biol. Chem. 249, 6684-6692). Apparently, the interaction of the distal carboxylate group of the substrate with Arg 292 underlies not only the binding specificity but also the kinetic specificity of aspartate aminotransferase for dicarboxylic substrates.

Aldehydes↗

PubMed1981

[Modification of blood serum mineral levels and aspartate aminotransferase, leucine aminopeptidase and alkaline phosphatase activity and plasma in glucose levels in healthy cattle by Ca-Mg-containing solutions].

Three high-performance cows in lactation were tested each for the effects of two kinds of infusion each, 500 ml of Tetamag-2 solution (60 g of calcium gluconate and 60 g of magnesium adipate) and 500 ml of Calcimag (100 g of calcium gluconate and 20 g of magnesium adipate), upon the levels of calcium, magnesium, Pa, potassium, and sodium as well as upon the activities of aspartate-aminotransferase, leucine-aminopeptidase, and alkaline phosphatase in blood serum and upon glucose levels in blood plasma. Migration of calcium out of blood plasma was found to take place at much higher rate than that of magnesium. Infusion of Pa and glucose was followed soon by some temporary drop of values. No directional effects were recordable from potassium and sodium. Aspartate-aminotransferase activity did not change in response to transfusion. Intravenous infusion of Tetamag-2 solution caused strong temporary rise in magnesium concentration and, consequently, activation of leucine-aminopeptidase.

Alkaline Phosphatase↗

PubMedDate not supplied

Changes in the activity of aspartate and alanine aminotransferase caused by aseptic inflammatory reaction and ionizing radiation in the liver, kidney and spleen of mice.

The activity of aspartate aminotransferase and alanine aminotransferase and the content of soluble proteins were determined in mice irradiated with single dose of 100 R or injected with turpentine and in mice subjected to both these stress factors. The aim of this study was determination of changes in the activity of both these enzymes in the liver, kidney and spleen within 48 hours). It was found that the action of both these stress factors caused significant changes in the activity of AspAT and A1AT in the first phase of the response of the organism to stress and caused statistically significant changes of this activity on the second day of the experiment.

Alanine Transaminase↗

PubMed1981

Direct immunological determination of aspartate aminotransferase isoenzymes.

We examined the suitability of a rapid immunological technique to determine the amount of aspartate aminotransferase (EC 2.6.1.1) isoenzymes in human serum or tissue extracts. Purified isoenzymes were absorbed as a monolayer to the surface of an indium metal film on glass. The enzyme retains immunological reactivity, allowing the specific binding of aspartate aminotransferase antibodies at the surface. The amount of isoenzyme in a specimen is estimated from the competition for the antibody between the free isoenzyme in the specimen and that at the surface. The surface is further incubated with goat antibodies to rabbit IgG, and the extent of antibody binding is determined by densitometry. There is no cross reactivity between the cytoplasmic and mitochondrial forms, so these two isoenzymes can be determined simultaneously. The minimum detectable concentration by this technique is about 50 micrograms of enzyme protein per liter. The within-day coefficient of variation for determination of either isoenzyme was about 20%. Our results suggest that normal and patients' sera contain considerably more immunologically active than catalytically active isoenzymes.

Aspartate Aminotransferases↗

PubMed1980

Improved serum-initiated aspartate aminotransferase assay by inhibition of lactate dehydrogenase with oxamate.

We describe a serum-inititated aspartate aminotransferase (EC 2.6.1.1) assay that obviates the need for added lactate dehydrogenase (EC 1.1.1.27) in the reagent system. Interference from the oxidation of NADH by endogeneous lactate dehydrogenase is eliminated by adding sodium oxamate, a competitive inhibitor of the enzyme. The advantages of oxamate inhibition over lactate dehydrogenase addition are a shorter preincubation period, an increase in the linear range from less than 600 to more than 1400 U/L, no interference from above-normal concentrations of ketoacids, and elimination of bias between serum-initiated and the standard oxoglutarate-initiated assays for aspartate aminotransferase.

Amino Acids↗

PubMedDate not supplied

Serum cytoplasmic and mitochondrial aspartate aminotransferase in Duchenne's progressive muscular dystrophy.

The activities of cytoplasmic and mitochondrial aspartate aminotransferase isoforms in serum in 20 outpatients with Duchenne's progressive muscular dystrophy and seven carriers of the gene of that disease were determined. The control group consisted of 19 patients with other neuromuscular disorders. Twenty, age-matched healthy persons comprised the normal control group. The activity of the cytoplasmic isoform was increased in 85% of Duchenne's dystrophy cases. In these cases the reaction of the cytoplasmic isoenzyme in the presence of pyridoxal 5'-phosphate was abnormal. In the remaining Duchenne's dystrophy cases normal activity of this isoform and normal stimulation to pyridoxal 5'-phosphate was found. The mitochondrial isoform was significantly increased in 30% of Duchenne's dystrophy cases. In all Duchenne's dystrophy patients the reaction of the mitochondrial isoenzyme to supplementation with pyridoxal 5'-phosphate was normal. We conclude that the evaluation of aspartate aminotransferase isoforms in serum in Duchenne's dystrophy can be of clinical importance, especially in evaluating the degree of muscle cell damage.

Aspartate Aminotransferases↗

PubMed1995

Multienzyme control serum (Seraclear-HE) containing human enzymes from established cell lines and other sources. 2: Evaluation as candidate working enzyme Reference Material for alanine and aspartate aminotransferases.

Seraclear-HE, containing seven enzyme analytes from human sources, was evaluated as an intermethod calibrator for aspartate aminotransferase (AST) and alanine aminotransferase (ALT) to transfer Reference Method values to seven routine methods, including one based on hydrogen peroxide detection for possible unification of values (interlaboratory comparability of data). The commutabilities of AST from erythrocytes and ALT from a hepatoma cell line were studied between the consensus methods of Japan Society of Clinical Chemistry (chosen as the Reference Methods) and each of the automated routine methods at reaction temperatures of 30 degrees C and 37 degrees C. For AST, calibration of patients' sera with Seraclear-HE decreased average intermethod variation (CV) from 12% to 2%; for ALT, the decrease was from 20% to 3%. For both enzymes, Seraclear-HE was judged to be commutable between the Reference Methods and each of the methods investigated. The limitations for such use are discussed.

Alanine Transaminase↗

PubMedDate not supplied

[Activity of alanine- and aspartate-aminotransferases in organs of albino rats subjected to whole body gamma-irradiation and physical exercise].

The investigations of enzyme activity such as aspartate aminotransferase (AST, KE 2.6.1.1.) and alanine aminotransferase (ALT, KE 2.6.1.2) playing an important role in proteins metabolism were carried out in cell fraction of rat liver, myocardial and skeleton muscle after the influence of ionizing radiation (6 Gy) and the maximum physical loading. It was shown that physical loading furthered the increase of ALT-activity in all cell fractions except liver cytosol. And it was noted a strongly pronounced tendency of AST-activity to lowering, except muscle cell fractions. ALT-activity level in irradiated animals showed phase changes dependent on the term of observation and the kind of investigated tissues. The primary lowering of AST-activity in cell fractions of the investigated tissues is a conformity to natural laws of the gamma-irradiation influence on AST in most cases. It was shown that the physical tiredness made worse penetrated radiation action on the investigated enzymes.

Alanine Transaminase↗

PubMed1994

Aspartate aminotransferase macroenzyme complex in serum identified and characterized.

Macromolecular aspartate aminotransferase was found in the serum of an apparently healthy patient. This complex was composed of aspartate aminotransferase (AST; EC 2.6.1.1) and immunoglobulin. Electrophoresis of the patient's serum showed an abnormal band migrating between mitochondrial (m) and cytosolic (s) AST. The macromolecular complex was purified by gel filtration on Sephacryl S300. The molecular mass of the complex was estimated to be 250 kDa, suggesting that the complex probably consists of one immunoglobulin molecule associated with one AST molecule. By immunoelectrophoresis, the immunoglobulin was found to be an IgG with kappa-lambda type light chain. When we used polyclonal antibodies against human mAST or sAST, the sAST antibodies strongly inhibited the AST activity of the macrocomplex, whereas the mAST antibodies had no effect. Thus the AST molecule of the macrocomplex is an sAST type.

Aged↗

PubMed1994

Crystalline mitochondrial aspartate aminotransferase exists in only two conformations.

The subunits of the alpha 2-dimeric enzyme aspartate aminotransferase are composed of two distinct domains, one large and one small. The active sites are situated close to both the intersubunit and the interdomain interface. Binding of substrate analogues to the active site induces a large conformational change in the enzyme, whereby the small domain rotates by 13 degrees relative to the large domain and completely buries the ligand. We have determined the crystal structures of chicken mitochondrial aspartate aminotransferase (mAATase) in two new crystal forms. A comparison of the structures of mAATase in five crystal forms, including both the unliganded and the liganded enzyme, shows that mAATase exists in either one of two unique conformations, with only minimal adaptations to the crystal lattice. This suggests that both the open, unliganded and closed, liganded structure of mAATase are, to a large extent, stabilized by intramolecular interactions, and are consequently representative of functional states of the protein in solution. A 2-fold-symmetric packing interaction between small domains occurring identically in three crystal forms of mAATase is described.

Animals↗

PubMed1994

Testis-specific transcription start site in the aspartate aminotransferase housekeeping gene promoter.

We have studied the expression and regulation of the rat testis cytosolic aspartate aminotransferase gene. The cytosolic aspartate aminotransferase activity was 5-fold lower in the testis than in the liver and kidney. A 1.9-kilobase mRNA form was detected in the rat testis in contrast to the 2.1- and 1.8-kilobase forms present in other organs. Using Northern blot and S1 mapping analyses, we found that the proximal polyadenylation site was almost exclusively used in the testis as opposed to other organs where the distal site was preferentially used. RNase protection and primer extension analysis showed that transcription was initiated at multiple sites in all organs, but the pattern of those start sites was different in the testis; in particular, a novel transcription start site was specifically detected in this organ (at position -115 from the translation start site). This site was first observed in 29-day-old rats and was maximally utilized in the adult testis. DNase I footprinting using testis nuclear extracts revealed the presence of three sites of DNA-protein interaction in the 250-base pair proximal promoter, a pattern similar to the one found using liver nuclear extracts. However, the proteins bound had different properties as shown by gel retardation experiments. We conclude that the pattern of transcription initiation and the polyadenylation site selection of a housekeeping gene can be tissue-specific.

Animals↗

PubMedDate not supplied

Transient increase of aminotransferases in RA patients treated with methotrexate.

Sixty-two patients with rheumatoid arthritis (RA) were treated with methotrexate (MTX) for 3 months. Methotrexate was given orally in a single dose of 7.5-15.0 mg/week. At the onset of the treatment increased activity of aminotransferases has been observed. Eighteen patients (29%) displayed higher enzyme activity in the first 3 weeks. Despite the continuous drug administration the activity of aminotransferase became normal at week 12 in all but one patient. In this patient MTX had to be withdrawn.

Adult↗

PubMed1993

[Increased activity of aminotransferases (ALAT, AspAT) in pregnant women threatened with immature and premature delivery treated with fenoterol].

2330 pregnant women were admitted to the 2nd Department of Pregnancy Pathology at the Polish Mother's Memorial Hospital (PMMH) in Lódź, Poland, during the period from 28th March, 1989 to 30th June, 1991. Out of the group 1055 pregnancies were treated because of the risk of premature delivery (45.28%). In five (5) cases a significant rise of ALAT and AspAT aminotransferase activity occurred during fenoterol therapy. Laboratory tests excluded infectious etiology in the rise of the enzymes in question (no markers typical for HBV, HAV infection). Toxic injury of hepatic cells being suspected, fenoterol therapy was withdrawn, followed by a decrease of aminotransferases activity to normal values in those five (5) cases. No increase in the activity of ALAT and AspAT occurred in further follow up of the pregnant women in pregnancy and in puerperium. Since no other hepatotoxic factors appeared, it may be assumed that a chronic administration of fenoterol can cause transient injuries of hepatic cells. For this reason all pregnant women treated with betamimetics require examinations of the liver.

Alanine Transaminase↗

PubMed1993

[Muscular exertion--"embarrassment" in the evaluation of aminotransferases and creatine kinase serum levels].

The authors draw attention to the problem of elevated values of aspartate aminotransferase (AST), alanine aminotransferase (ALT) and creatine kinase (CK) serum activities in adolescents which they encountered recently in two patients hospitalized in their clinic. In common practice it is important when evaluating results of ALT, AST and CK in serum to take into account the effect of physical load, encountered frequently in this age group of adolescents.

Adolescent↗

PubMed1977

Biological variability in aspartate aminotransferase activity in serum of healthy persons, and effect of in vitro supplemantation with pyridoxal 5-phosphate.

Aspartate aminotransferase (EC 2.6.1.1) activities in sera from nine healthy individuals were monitored during two weeks, both with and without first supplementing the serum with pyridoxal phosphate. Pyridoxal phosphate supplementation caused a mean increase of 39% (range, 33-55%) in measured activity. The biological variability during the two-week period was independent of pyridoxal phosphate supplemantation. The intra-individual variability (CV) was 5.3% and 5.1% with and without pyridoxal phosphate supplementation, respectively; the corresponding inter-individual variability was 13.2% and 13.6%. We conclude that the reference interval will be insensitive to intra-individual fluctuations in aspartate aminotransferase activity in serum, whether or not the serum is supplemented with pyridoxal phosphate.

Adult↗

PubMed1993

[Contribution of liver biopsy and serology of hepatitis C virus to the diagnosis of a moderate and prolonged elevation of aminotransferases].

The aim of this study was to evaluate the diagnostic usefulness of percutaneous liver biopsy and screening for hepatitis C virus antibodies with 1st and 2nd generation ELISA in asymptomatic blood donors with persistent (> 1 year) and moderate elevation (> 1.5 times the upper limit of normal) of serum alanine aminotransferase. The diagnosis was established from clinical, biological and ultrasound data before biopsies were obtained, then compared to the histological diagnosis. Thirty one of 56 blood donors who satisfied the preceding criteria accepted liver biopsy and were subsequently included in the study. An accurate diagnosis was proposed before biopsy in 20 cases. This was in agreement with the histological results in 19 cases but in 2 of these, unexpected lobular hepatitis was associated with the expected steatosis. Positive hepatitis C virus tests corresponded to chronic hepatitis in all cases (n = 5). No accurate diagnosis could be proposed in the 11 remaining cases owing to the lack of evidence of any etiology (n = 4) or because several potential etiologies were possible for the same subject (n = 7). Histological diagnoses were: isolated steatosis (n = 12), steatosis associated with lobular hepatitis (n = 7) or with chronic persistent hepatitis (n = 1), chronic active (n = 2) or chronic persistent hepatitis (n = 3), alcoholic hepatitis (n = 2), hemochromatosis (n = 1), and normal liver (n = 3). Liver biopsy is essential to the accurate etiological diagnosis of persistent and moderate elevation of aminotransferases despite hepatitis virus C tests which are associated with the correct diagnosis of chronic hepatitis in 16% of cases.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗