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PubMed2003

[Clinico-morphological characteristics of chronic HbcAg-negative HBV infection with a normal level of aminotransferases].

To study clinicomorphological characteristics and a course of chronic HbeAg-negative HBV-infection with a normal level of aminotransferases, 38 patients whose blood contained HbsAg, HBVDNA and anti-Hbe were divided into 2 groups: with normal (20 patients, test group) and elevated (18 patients, control group) level is of aminotransferases. All the patients' livers were studied morphologically and semiquantitative test for viremia was made. Compared to the controls, the test group patients had low morphological activity (3.4 +/- 1.1 and 8.7 +/- 3.2, respectively, p < 0.005), a fibrosis degree (1.1 +/- 0.4 and 2.3 +/- 1.4 score, respectively p < 0.01) and viremia (log 10 - 3.7 +/- 1.2 vs 6.1 +/- 2.4, p < 0.05). The monofactor analysis has established that viremia 10(5) cop/ml maximum significantly associates with a normal level of aminotransferases (chi-square = 7.89, p = 0.005) while viremia higher than 10(7) cop/ml strongly correlates with a high level of aminotransferases (chi-square = 4.11, p = 0.043). Follow-up of patients with a normal level of aminotransferases for 28 +/- 24 months (6-72 months) showed neither deterioration of the clinical status nor laboratory changes. Thus, patients having anti-HBe and no HbeAg with a normal level of ALT and low viremia (under 10(5) cop/ml) can be considered inactive carriers of HbsAg. In spite of a relatively favourable prognosis, these patients should be followed up for a long time.

Adult↗

PubMed1975

Inhibitory effect of cortisone acetate on the stimulation of rat liver cytosol L-serrine. Pyruvate aminotransferase by dibutyryl adenosine 3,5-monophosphate.

An injection of cortisone acetate at a dose of 5 mg/100 g body weight concomitant with dibutyryl cyclic AMP prevents the increase in the activity of rat liver cytosol serine aminotransferase (L-serine:pyruvate aminotransferase, EC 2.6.1.51) elicited by the nucleotide with a lag of about 2 h. If the glucocorticoid is given 2 h prior to the nucleotide inducer, the lag disappears. The inhibitory effect of cortisone acetate gradually decays and is no longer detectable 12 h following its administration. Theophylline, insulin and glucose at doses which affect significantly the level of tyrosine aminotransferase, have not effect on the level of serine aminotransferase and on the cortisone inhibition. The inhibitory effect of the glucocorticoid on the dibutyryl cyclic AMP-mediated increase in serin aminotransferase diminishes with the age of animall. Increases in the enzyme activity by a single dose of glucagon can also be inhibited by cortisone acetate and actinomycin D as in the case with dibutyryl cyclic AMP as an inducer. The possibility of the existence of a specific inhibitory factor which is formed in response to cortisone acetate is discussed.

Age Factors↗

PubMed1977

Nucleus-dependent regulation of tyrosine aminotransferase degradation in hepatoma tissue culture cells.

Upon removal of the nucleus from rat hepatoma tissue culture cells, levels of the enzyme tyrosine aminotransferase no longer change in response to withdrawal of glucocorticoids. The rate of tyrosine aminotransferase degradation is drastically reduced in rat hepatoma tissue culture cytoplasts leading to stabilization of pre-existing levels of tyrosine aminotransferase. Moreover, the rate of synthesis of the enzyme in cytoplasts is very low near that observed in uninduced whole cells. These effects of enucleation occur very rapidly and appear to be specific for tyrosine aminotransferase and a small number of other unstable hepatoma proteins. A nuclear effect is thus directly involved in the control of tyrosine aminotransferase degradation and synthesis.

Carcinoma, Hepatocellular↗

PubMed1990

Interaction of L-canaline with ornithine aminotransferase of the tobacco hornworm, Manduca sexta (Sphingidae).

Ornithine aminotransferase (L-ornithine:2-oxo-acid aminotransferase (EC 2.6.1.13)) has been purified to homogeneity from last instar larvae of the tobacco hornworm, Manduca sexta (Sphingidae). This enzyme is a 144,000-Da tetramer constructed from 36,000-Da protomeric units. It has a high aspartate/asparagine and glutamate/glutamine content and 2 cysteine residues/subunit. All 8 cysteine residues can react with N-ethylmaleimide to inactivate the enzyme. Maintenance of the enzyme in the presence of 2-mercaptoethanol and dithiothreitol maximizes enzymatic activity and improves storage conditions, presumably by protecting these sulfhydryl groups. The apparent Km values for L-ornithine and 2-oxoglutaric acid are 2.3 and 3.2 mM, respectively. The turnover number is 2.0 +/- 0.1 mumol min-1 mumol-1. L-Canaline (L-2-amino-4-(aminooxy)butyric acid) is a potent ornithine aminotransferase inhibitor. Reaction of the enzyme with L-[U-14C]canaline produces an enzyme-bound, covalently linked, radiolabeled canaline-pyridoxal phosphate oxime. The L-[U-14C]canaline-pyridoxal phosphate oxime has been isolated from canaline-treated enzyme. Dialysis of canaline-inactivated ornithine aminotransferase against free pyridoxal phosphate slowly reactivates the enzyme as the oxime is replaced by pyridoxal phosphate. Analysis of L-[U-14C]canaline binding to ornithine aminotransferase reveals the presence of 4 mol of pyridoxal phosphate/mol of enzyme.

Amino Acids↗

PubMed1989

A review of donor alanine aminotransferase testing. Implications for the blood donor and practitioner.

To reduce the incidence of post-transfusion non-A, non-B hepatitis, the American Association of Blood Banks has required that serum alanine aminotransferase activity be used to screen blood donors. Consequently, approximately 2% to 3% of all blood donations will be discarded owing to an elevated alanine aminotransferase level. In addition, approximately 0.7% of blood donors will be notified of an abnormal alanine aminotransferase result. While some of these donors may have viral hepatitis, factors such as the donor's age, gender, body weight, ethnic background, alcohol intake, diet, and exercise must also be considered when interpreting an elevated alanine aminotransferase level. Donors with significant or persistently elevated alanine aminotransferase levels should have their conditions evaluated so that treatable diseases can be recognized and/or treated.

Alanine Transaminase↗

PubMed1985

[Hormonal induction of tyrosine aminotransferase and RNA synthesis in the cells of Morris hepatoma strain 7777].

The transfer of Morris hepatoma cells induced by the hormone within 10-60 min in to a hormone-free medium is associated with the augmentation of tyrosine aminotransferase synthesis. The kinetics of this process does not differ from that of the hormone-induced enzyme. The return of tyrosine aminotransferase synthesis to the basal level occurs 15-20 hours after the hormone withdrawal from the medium, although the concentration of the intranuclear hormone sharply decreases already after 3 hours. It was demonstrated that the presence in the hepatoma cell nuclei of 20-25% of the initially bound hormone for at least 20 hours after the cell transfer to the hormone-free medium is not sufficient for maintaining a high level of tyrosine aminotransferase gene expression. Using two-dimensional electrophoresis of 3H-labeled hepatoma cell proteins, it was demonstrated that the observed high activity of tyrosine aminotransferase is due to the de novo synthesis of enzyme molecules rather than to the existence of preformed long-living tyrosine aminotransferase molecules inside the cell. Study of [14C]uridine incorporation into non-ribosomal nuclear RNA of hepatoma cells showed a long-term presence of the label in the RNA throughout the chase experiment. It was assumed that the high activity of the enzyme for 10-15 hours after the hormone release from the hepatoma cell nuclei is due to the accumulation in the nuclei of long-living pre-mRNA molecules synthesized after the hormone addition to the cells and during the first hours after the cell transfer to the hormone-free medium.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1986

In vitro phosphorylation of 4-aminobutyrate aminotransferase by cAMP dependent protein kinase.

Highly purified 4-aminobutyrate aminotransferase from pig brain is susceptible to phosphorylation by the purified cAMP-dependent protein kinase catalytic subunit. Up to 0.7 moles of phosphate from ATP-(gamma)-32P can be incorporated per mole of dimeric holoenzyme. Maximum phosphorylation was observed within about 90 minutes at 30 degrees C. Despite the extensive degree of phosphorylation observed, no kinetic property of the enzyme was perceptibly altered. Removal of cofactor had no detectable impact on the extent of phosphorylation but thermal inactivation of the enzyme increased and mild reduction with sodium borohydride decreased the phosphorylatability of the aminotransferase. It was possible to separate the enzyme into phospho and dephospho forms by the use of DEAE chromatography. Validation that the two fractions represented genuine aminotransferase was obtained by proteolytic peptide mapping. The phospho form of the enzyme was found to possess little or no aminotransferase activity while that of the dephospho form exhibited higher specific activity than the purified enzyme prior to phosphorylation. Furthermore, the dephospho form of the enzyme could not be detectably phosphorylated by reincubation with the kinase following DEAE chromatography unless it was subjected to thermal inactivation. The stoichiometry of phosphorylation of the fraction containing 32P from DEAE chromatography was approximately 1 mole/mole of dimer. These results suggest that the substrate for phosphorylation by the kinase is a form of the aminotransferase which is somehow inactivated during routine purification even when extensive precautions are taken to maximally preserve catalytic activity.

4-Aminobutyrate Transaminase↗

PubMed1983

Translational and pretranslational control of ornithine aminotransferase synthesis in rat liver.

The mitochondrial matrix enzyme, ornithine aminotransferase, is induced in rat liver by the administration of a diet high in protein and by glucagon. The rate of synthesis of the enzyme is increased 100-fold in the livers of rats maintained on a 60% relative to a 0% protein diet, whereas the levels of functional and hybridizable mRNA measured by in vitro translation and through the use of a cloned cDNA probe increased by only 2- to 6-fold and 2- to 3-fold, respectively. Under conditions of glucagon induction that resulted in a 10- to 12-fold increase in the rate of enzyme synthesis, the relative level of functional ornithine aminotransferase mRNA increased by only 2-fold, and the level of hybridizable mRNA actually decreased. The rate of polypeptide chain elongation and the relative number of ornithine aminotransferase nascent chains on polysomes were 2-fold and 23-fold greater, respectively, in hepatocytes derived from 60% relative to 0% protein-fed rats. Using these data, a 23-fold increase in the translational efficiency of the mRNA was calculated. This increase, along with a 2-fold increase in the mRNA level, completely account for the 40-fold increase in the rate of ornithine aminotransferase synthesis observed in hepatocytes derived from 60% protein-fed rats. We conclude that ornithine aminotransferase synthesis is regulated at both a translational and a pretranslational level in rat liver.

Animals↗

PubMed1983

Induction of tyrosine aminotransferase activity by concanavalin A in cultured rat hepatoma cells.

Concanavalin (Con A) induced tyrosine aminotransferase activity in cultured rat hepatoma cells (R117-21B). The highest level of the induced enzyme activity was observed at 6 to 8 hr of incubation with Con A, and the activity returned to the control level after 24 hr. This enzyme induction was dose-dependent in the range of 0.5 to 5 micrograms Con A per ml, while at higher concentrations (more than 50 micrograms/ml) the induction was very small or absent. The addition of alpha-methyl-D-mannoside abolished the effect of Con A. A 4 hr incubation of the cells with Con A and a subsequent 2 hr incubation was necessary to yield the maximal induction of tyrosine aminotransferase activity. Simultaneous incubation of the cells with Con A (5 micrograms/ml) and insulin or dexamethasone, induced tyrosine aminotransferase activity to levels higher than each activator alone, and the effect of Con A on the induction of tyrosine aminotransferase activity by dexamethasone was almost an additive. It was concluded that Con A at low concentrations mimics insulin in the induction of tyrosine aminotransferase activity in R117-21B cells, and that the effect of Con A and insulin on the induction of the enzyme is different from the effect of dexamethasone on this process.

Animals↗

PubMed1982

In vitro synthesis and processing of a precursor to ornithine aminotransferase.

Poly(A)+ RNA was isolated from liver-free polysomes of rats maintained on a 60% casein diet by sodium dodecyl sulfate-phenol-chloroform extraction and oligo(dT)-cellulose chromatography. Poly(A)+ RNA translated in a rabbit reticulocyte lysate system produced a polypeptide of 49,000 daltons that was immunoprecipitated by monospecific, affinity-purified IgG antibodies to ornithine aminotransferase (ornithine-oxo acid aminotransferase, EC 2.6.1.13). This polypeptide is 6,000 daltons larger than mature ornithine aminotransferase when electrophoresed on sodium dodecyl sulfate polyacrylamide gels. One-dimensional peptide mapping demonstrated that this 49,000-dalton polypeptide is structurally related to ornithine aminotransferase. Furthermore, it can be processed to a polypeptide of 43,000 daltons by a rat liver mitochondrial fraction. We have concluded that this polypeptide is a precursor to ornithine aminotransferase.

Animals↗

PubMed1976

[Histochemical evidence of aminotransferases. VII. Quantitative histochemical and biochemical investigations of the amino-transferases of branched chain amino acids, glycine and serine in the rat organs during development (author's transl)].

Ontogenetic changes of the activity and isoenzymes of the aminotransferases of branched chain amino acids, glycine and serine in the rat organs have been studied by quantitative histochemical method and by electrophoresis. An increase of the enzymatic activity with the 3 branched chain amino acids has been observed up to the 7th day after birth. Thereafter the changes with leucine and isoleucine are rather similar. The intensity of the specific leucine aminotransferase isoenzymes in the liver and the brain gradually increase in the development. Despite this, the nonspecific isoenzymes are available only in the embryonic and early postnatal stages. Glycine- and serine aminotransferases show relatively similar pattern of activity and more prominent change between the 7th and 14th postnatal day. The variant pattern of the aminotransferase activity in the growing rats is discussed with regard to the metabolic, structural and hormonal changes in the development. The differences in the activity of one and the same aminotransferase or its isoenzymes in the organs are most probably related to the functional differentiation.

Animals↗

PubMed1993

Isolation and characterization of recombinant mitochondrial 4-aminobutyrate aminotransferase.

4-Aminobutyrate aminotransferase, which catalyzes the conversion of 4-aminobutyrate to succinic semialdehyde, is a key enzyme of the 4-aminobutyrate shunt. The amino acid sequence predicted from the cDNA sequence shows that the precursor protein consists of the mature enzyme of 473 amino acid residues and an amino-terminal segment of 27 amino acids (Kwon, O. S., Park, J., and Churchich, J. E. (1992) J. Biol. Chem. 267, 7215-7216). A recombinant 4-aminobutyrate aminotransferase has been expressed in Escherichia coli using pETIId as expression vector. The protein has been purified and characterized as a dimer (2 x 55 kDa). NH2-terminal sequence analysis has revealed the presence of an extra amino-terminal segment (signal peptide) predicted from the cDNA sequence. The isolated precursor of 4-aminobutyrate aminotransferase contains pyridoxal 5-phosphate and exhibits catalytic activity (18 units/mg) comparable to that of the mature enzyme (20 units/mg). The presequence peptide of the precursor of mitochondrial 4-aminobutyrate aminotransferase does not interfere with the folding and functional properties of the mature moiety of the aminotransferase.

4-Aminobutyrate Transaminase↗

PubMed1989

The nature of unexplained chronic aminotransferase elevations of a mild to moderate degree in asymptomatic patients.

To determine the nature of unexplained chronic serum aspartate aminotransferase elevations of a mild to moderate degree in asymptomatic patients, we performed systematic clinical, biochemical and histologic examinations in 47 individuals who had been screened for virus-, alcohol- or drug-related disease. Serum aspartate aminotransferase levels ranged from 3- to 8-fold normal (mean: 156 +/- 7 units per liter) for at least 6 months (mean: 30 +/- 6 months). Serum alanine aminotransferase levels were also increased but to a lesser degree in most patients. Thirty-four patients (72%) had histologic features of chronic active hepatitis, including 16 with cirrhosis. Ten patients (21%) had steatohepatitis and three (6%) had miscellaneous disorders. Patients with chronic active hepatitis and cirrhosis could not be distinguished from counterparts without cirrhosis by individual clinical or laboratory findings. Antinuclear or smooth muscle antibodies were detected in 18 of the patients with chronic active hepatitis (53%). All patients with steatohepatitis were women, and they had laboratory changes at presentation, including seropositivity for antinuclear antibodies, that overlapped with those of patients with chronic active hepatitis. We conclude that asymptomatic patients with unexplained chronic aspartate aminotransferase elevations of a mild to moderate degree frequently have chronic active hepatitis and that many have cirrhosis. Immunoserologic findings compatible with autoimmune hepatitis are commonly present. Steatohepatitis is the most frequent alternative diagnosis, especially in women, and it is not excluded by the presence of antinuclear antibodies. Differentiation of the disorders is possible only by histologic examination.

Adult↗

PubMed2004

Crystal structure of a putative aspartate aminotransferase belonging to subgroup IV.

Protein TT0402 from Thermus thermophilus HB8 exhibits about 30-35% sequence identity with proteins belonging to subgroup IV in the aminotransferase family of the fold-type I pyridoxal 5'-phosphate (PLP)-dependent enzymes. In this study, we determined the crystal structure of TT0402 at 2.3 A resolution (R(factor) = 19.9%, R(free) = 23.6%). The overall structure of TT0402 exhibits the fold conserved in aminotransferases, and is most similar to that of the Escherichia coli phosphoserine aminotransferase, which belongs to subgroup IV but shares as little as 13% sequence identity with TT0402. Kinetic assays confirmed that TT0402 has higher transamination activities with the amino group donor, L-glutamate, and somewhat lower activities with L-aspartate. These results indicate that TT0402 is a subgroup IV aminotransferase for the synthesis/degradation of either L-aspartate or a similar compound.

Amino Acid Sequence↗

PubMed1997

Cloning and sequencing of aspartate aminotransferase from Thermus aquaticus YT1.

A 39-base oligonucleotide "guessmer" probe, based on partial N-terminal sequence analysis of the aspartate aminotransferase purified from Thermus aquaticus strain YT1, was used to screen a genomic library prepared from T. aquaticus DNA. A 1842 bp DNA fragment was isolated that proved to contain the coding sequence for the aspartate aminotransferase. The gene is 1152 bases long and codes for a protein of 383 amino acid residues. The amino acid sequence obtained showed 88.7%, 45.1% and 32.9% identity of sequence with those of thermostable aspartate aminotransferases from T. thermophilus, Bacillus YM2, and Sulfolobus solfataricus, respectively. It showed 39.1% identity with one of the gene products tentatively identified as aspartate aminotransferase from the methanogenic archaebacterium Methanococcus jannaschii. Neither the amino acid compositions nor the aligned amino acid sequences provides any obvious clue as to the origin of thermal stability in this group of enzymes.

Amino Acid Sequence↗

PubMed1987

Aminotransferase changes in burned patients.

The time course of serum transaminases (alanine aminotransferase and aspartate aminotransferase) has been followed in 30 selected consecutive patients presenting burn sizes ranging from 10% to 95% of the total body surface (mean 43.13) and a survival index from 0.99 to 0.00 (mean 0.59). The results show that in all the patients both transaminases change in parallel, increasing in 18 patients (60%). In nearly all patients both enzymes increase during the second week after injury and aspartate aminotransferase increases later than alanine aminotransferase. The higher transaminase levels are noted in moderately ill patients. No clear correlation between the overall increase of transaminases and the extent of burned surface area has been found. We conclude that functional liver alterations mostly contribute to the increase of serum transaminases in burns.

Adolescent↗

PubMed1994

Aspartate aminotransferase and glutaminase activities in rat olfactory bulb and cochlear nucleus; comparisons with retina and with concentrations of substrate and product amino acids.

The quantitative distributions of aspartate aminotransferase and glutaminase were mapped in subregions of olfactory bulb and cochlear nucleus of rat, and were compared with similar data for retina and with the distributions of their substrate and product amino acids aspartate, glutamate, and glutamine. The distributions of both enzymes paralleled that of aspartate in the olfactory bulb and that of glutamate in the cochlear nucleus. In retina (excluding inner segments), there were similarities between aspartate aminotransferase and both glutamate and aspartate distributions. The distribution of gamma-aminobutyrate (GABA) was similar to those of both enzymes in olfactory bulb, to aspartate aminotransferase in cochlear nucleus, and to glutaminase in retina (excluding inner segments). The results are consistent with significant involvement of aspartate aminotransferase, especially the cytosolic isoenzyme, and glutaminase in accumulation of the neurotransmitter amino acids glutamate, aspartate, and GABA, although with preferential accumulation of different amino acids in different brain regions.

Amino Acids↗

PubMed1987

Quantitation of aspartate aminotransferase isoenzymes after electrophoretic separation.

A scheme for the quantitative detection of aspartate aminotransferase isoenzymes and multiple forms after electrophoretic separation is described. Glutamate generated from the aminotransferase reaction is quantitated by using the glutamate dehydrogenase/diaphorase-coupled enzyme system to form a formazan dye. Product inhibition of aspartate aminotransferase by oxaloacetate is prevented by including oxaloacetate decarboxylase in the overlay reagent. Results compare favorably with those of an immunochemical precipitation procedure. The method can also be used to detect quantitatively subforms and atypical forms (genetic variants, immunoglobulin-enzyme complexes) of aspartate aminotransferase.

Animals↗