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At least 757 records · Page 42Linked to original sources

PubMed1993

A study of branched-chain amino acid aminotransferase and isolation of mutations affecting the catabolism of branched-chain amino acids in Saccharomyces cerevisiae.

The specific activity of branched-chain amino acid aminotransferase was highest when S. cerevisiae was grown in minimal medium containing a branched-chain amino acid as nitrogen source. Growth in complex media with glycerol or ethanol gave moderately high levels, whereas with glucose and fructose the specific activity was very low. Mutagenesis defined three genes (BAA1 to BAA3) required for branched-chain amino acid catabolism. The baa1 mutation reduced the specific activity of the aminotransferase, the stationary phase density in YEPD and caused gross morphological disturbance. Branched-chain amino acid aminotransferase is essential for sporulation.

Amino Acids, Branched-Chain↗

PubMed1991

Interaction of 5-azacytidine and dexamethasone in the control of hepatic tyrosine aminotransferase.

The nucleoside analog 5-azacytidine is able to induce tyrosine aminotransferase several-fold in the liver of suckling rats. Bilateral adrenalectomy abolishes this inducing effect. The drug also decreases significantly the concentration of cytosolic glucocorticoid receptor accompanied by an increase of the glucocorticoid receptor concentration in the nuclei. The antiglucocorticoid RU 486 which abolishes the induction of tyrosine aminotransferase and serine dehydratase by dexamethasone very effectively is not able to inhibit either the induction of tyrosine aminotransferase or the translocation of the glucocorticoid receptor into the nuclei by 5-azacytidine.

Animals↗

PubMed1984

Kinetics of 4-aminobutyrate:2-oxoglutarate aminotransferase from Nippostrongylus brasiliensis.

A gamma-aminobutyric acid transferase (4-aminobutyrate:2-oxoglutarate aminotransferase; EC 2.6.1.19) preparation from Nippostrongylus brasiliensis was found to contain only one peak of enzyme activity with a highly basic pI of 10.5 when analysed by isoelectric focusing and chromatofocusing. This material was used in kinetic studies to demonstrate that the parasite enzyme reaction mechanism conforms to the usual binary, non-sequential ('Bi Bi Ping Pong') type found with aminotransferases. The Km for 4-aminobutyrate was 0.33 mM, the Km for 2-oxoglutarate was 0.57 mM and Ki for glutamate was 0.35 mM. In holoenzyme reconstitution experiments with the cofactor, pyridoxal 5-phosphate, the KD was 1.54 microM. The values are comparable to those reported for other tissues. Only 2-oxoglutarate could function as the keto acid substrate whereas several amino acids besides 4-aminobutyrate (beta-alanine, alpha-L-alanine, L-aspartate and L-arginine) could apparently act as substrate although the possible presence of other amino acid:2-oxoglutarate aminotransferases was not excluded. In preliminary studies on the usefulness of conventional substrate analogues as parasite gamma-aminobutyric acid transferase inhibitors only canaline was effective.

4-Aminobutyrate Transaminase↗

PubMed1996

Phosphoserine aminotransferase from Bacillus circulans subsp. alkalophilus: purification, gene cloning and sequencing.

Two peaks of aspartate aminotransferase (AspAT) catalytic activity were observed during DEAE chromatography of a protein extract from alkalophilic B. circulans. The enzyme purified from the major peak appeared to be not aspartate but phosphoserine aminotransferase (PSAT) with a considerably high AspAT side activity. The sequence of the enzyme N-terminus was determined, and the PSAT gene was cloned as two separate fragments. DNA sequencing revealed the open reading frame for the PSAT starting from TTG, putative ribosomal binding site and terminator of transcription. The PSAT gene encodes a protein of 361 amino acids (M(r) 39793) which shows moderate homology to other known phosphoserine aminotransferases (36-46% of identity, 60-64% of similarity). The PSAT from the alkalophile shares with all of them the consensus sequence pattern around the pyridoxal 5'-phosphate attachment site.

Amino Acid Sequence↗

PubMed1982

Concanavalin A alters the turnover rate of tyrosine aminotransferase in cultured hepatoma cells.

Concanavalin A added to monolayer cultures of Reuber H-35 hepatoma cells caused a rapid inactivation of tyrosine aminotransferase (L-tyrosine:2-oxoglutarate aminotransferase, E.C. 2.6.1.5) and loss of reactivity with antibody against the native, dimeric enzyme. Analysis of treated cells with an antibody raised against carboxymethylated, denatured enzyme showed that the inactivated enzyme was reactive with this reagent, which does not react with the native enzyme. Subsequent addition of alpha-methyl-D-mannopyranoside to remove concanavalin A restored both enzyme activity and reactivity to antibody against native enzyme. After long-term treatment with concanavalin A, the restored enzyme levels were significantly higher than in controls treated with the sugar but not the lectin. Analysis of the turnover of the enzyme by two methods revealed that the rate of its degradation is reduced about 2-fold in concanavalin A-treated cells. Treatment with H-35 cells with concanavalin A thus effects an alteration in conformation of tyrosine aminotransferase, rendering it somewhat less sensitive to intracellular degradation.

Animals↗

PubMed1989

L-Histidinol phosphate aminotransferase from Salmonella typhimurium. Kinetic behavior and sequence at the pyridoxal-P binding site.

A coupled assay with alpha-hydroxyglutarate dehydrogenase was used to analyze the kinetic behavior of histidinol phosphate aminotransferase from Salmonella typhymurium. Data obtained from studies of initial velocity, inhibition by products or substrate analogues, isotope exchange rates, and the determination of the equilibrium constant were consistent only with a Ping-Pong Bi Bi mechanism. Variations in inhibition patterns by different substrate analogues indicate that the microenvironment about the pyridoxal phosphate and the pyridoxamine phosphate forms of histidinol phosphate amino-transferase are different, and favor the presence of one active site with partially overlapping substrate-binding subsites for these 2 forms of the enzyme. Histidinol phosphate aminotransferase also catalyzes decomposition of beta-chloro-L-alanine to pyruvate, NH3 and Cl-; no transamination of this substrate occurs and inactivation of the enzyme accompanies this reaction. After reduction of histidinol-P aminotransferase with [3H]NaBH4, carboxymethylation, and tryptic digestion, one major radioactive peptide absorbing at 325 nm was isolated. Its primary structure was determined to be TLSK*AFALAGLR, where K* is the P-pyridoxyllysine residue. Although this peptide is only 30-40% homologous with the corresponding segment reported for other transaminases, all of these peptides are similar in placement of an hydroxyamino acid residue three residues upstream from the lysine residue, and in the cluster of hydrophobic amino acid residues immediately following the lysine residue.

Binding Sites↗

PubMed1977

Interconversion of multiple forms of tyrosine aminotransferase in vitro and in vivo in cultured hepatoma cells.

Corticosteroid-induced tyrosine aminotransferase (EC 2.6.1.5) from cultured hepatoma cells was separated by carboxymethyl-Sephadex chromatography into three molecular forms resembling those described previously in the rat liver. Enzyme forms were isolated and used as purified substrates to examine their in vitro interconversion by various subcellular fractions. Isolated form III was converted to forms II and I, and isolated form II was converted to form I by the coarse particulate fraction sedimenting at 1000 X g. This activity was inhibited by the serine enzyme inhibitor phenylmethane sulfonyl fluoride or by raising the pH to 8.7. Conversion of enzyme forms in vitro in the opposite direction (I leads to II leads to III) could not be detected. The distribution of enzyme forms in vivo was examined by the use of experimental conditions that prevent their in vitro interconversion during cell extraction. Tyrosine aminotransferase extracted from cell subjected to various treatments that affect the rates of enzyme synthesis or degradation existed always predominantly as form III. It appears, therefore, that multiple forms of tyrosine aminotransferase are not related to the turnover of this enzyme in vivo.

Carcinoma, Hepatocellular↗

PubMed1982

Ornithine oxoacid aminotransferase found in AH 130 ascites hepatoma cells.

We found heterogenous ornithine oxoacid aminotransferase (L-ornithine: 2-oxo-acid aminotransferase, EC 2.6.1.1.3) in rat ascites hepatoma AH 130 cells. Compared with enzymes from normal rat tissues, this heterogenous enzyme showed larger Km values for 2-oxoglutarate, a different elution-profile upon affinity chromatography with 2-oxoglutarate, more anionic mobility upon polyacrylamide gell electrophoresis, and a clearly different salting-out property upon ammonium sulfate fractionation. Similar heterogeneity of this aminotransferase was found in human cancer cells.

Animals↗

PubMed1986

The level of beta-alanine aminotransferase activity in regenerating and differentiating rat liver.

beta-Alanine aminotransferase from rat liver was purified to electrophoretic homogeneity. The immunological and kinetic properties of this enzyme were similar to those of the enzyme from rat brain. However, the liver enzyme transaminates from beta-alanine to 2-oxoglutaric acid, while the brain enzyme transaminates from gamma-aminobutyric acid. beta-Alanine aminotransferase activity in regenerating rat liver was lower than that in control rat liver. Activity of this enzyme, as well as of other uracil-catabolizing enzymes (Weber, G., Queener, S.F. and Ferdinandus, A. (1970) in Advances in Enzyme Regulation (Weber, G., ed.), Vol. 9, pp. 63-95, Pergamon Press, Oxford), was low in newborn rat liver and increased about 5-fold, reaching the level observed in adult rat liver. beta-Alanine and prednisolone induced beta-alanine aminotransferase in rat liver.

Age Factors↗

PubMed1979

L-serine dehydratase and L-serine-pyruvate aminotransferase activities in different animal species.

1. A rough inverse correlation between liver serine dehydratase activity and species body size was observed with mammals. This was not found for glutamate, malate or lactate dehydrogenase, fumarase or aspartate-2-oxoglutarate aminotransferase. Serine dehydratase (and certain liver aminotransferases showing a similar species-size dependence) may have a role in the stimulation of heat production. 2. Cold-exposed rats showed a 3-4 fold increase in serine dehydratase activity. 3. No liver serine dehydratase was measurable in amphibia. 4. In mammals high liver serine-pyruvate aminotransferase is associated with a flesh-eating dietary habit. High activity was found in amphibia and goldfish. A gluconeogenic role is suggested.

Animals↗

PubMed1984

Tyrosine aminotransferase activity of frog (Rana esculenta) liver. III. A circannual study.

A circannual study of tyrosine aminotransferase and other metabolic enzymes in frog liver is reported. The subcellular distribution of all enzymatic activities under investigation was also studied. Results show significant oscillations of all enzymatic activities throughout the year; in particular tyrosine aminotransferase has a marked summer maximum. The subcellular distribution of tyrosine aminotransferase shows significant variations: the soluble activity of the enzyme presents a bimodal circannual distribution, which has its counterpart in an increased activity of heavier fractions.

Acid Phosphatase↗

PubMed1988

Alanine:glyoxylate aminotransferase activities in liver of Suncus murinus (insectivora).

1. The distribution of L-alanine:glyoxylate aminotransferase (AGT) activities were found in Suncus liver, 55% in particulate fraction and 45% in supernatant. 2. 65% of AGT activities in particulate were dependent on AGT isoenzyme 2 (AGT 2) having molecular weight 210,000, the remainder (35%) of AGT activities were dependent on AGT isoenzyme 1 (AGT 1) which have aminotransferase activity for serine. AGT activities in supernatant were dependent on AGT 1, AGT 2 and alanine:2-oxoglutarate aminotransferase (GPT), and their activity ratios were 10, 15 and 75%, respectively. 3. Km values for alanine were 0.52 mM; AGT 1, 3.3 mM; AGT 2, 0.88 mM; GPT measuring with AGT activity. AGT activity of GPT was inhibited by addition of glutamate and its Ki value was 1.8 mM. 4. Some other properties of AGT 1, AGT 2 and GPT are described.

Alanine Transaminase↗

PubMed1987

Influence of oxypangam upon the induction of tyrosine aminotransferase, the NAD content and the ADPR transferase activity in several organs of the rat.

Oxypangam is a substance applied therapeutically against a number of diseases, such as chronic liver damages, angina pectoris, and psychosomatic disturbances. The mode of action of oxypangam has not yet conclusively been described. The only well-known properties of this substance are its intensive methylating and lipolytic effects. The present paper serves to elucidate the influence of oxypangam on the induction of the tyrosine aminotransferase, on the NAD content and on the activity of the ADPR transferase in the liver. Our studies showed that in normal animals, increasing doses of oxypangam support the induction of tyrosine aminotransferase. Up to a concentration of 100 mg/kg oxypangam enhances also the induction of tyrosine aminotransferase by tryptophan. In both cases, however, it does not work in adrenalectomized animals. Under the influence of oxypangam the NAD content of the liver remained unchanged, while the activity of the ADPR transferase was influenced only slightly.

Animals↗

PubMed2004

Natural history of hepatitis B e antigen to antibody seroconversion in patients with normal serum aminotransferase levels.

BACKGROUND: Natural history studies of hepatitis B virus infection have shown relapse of hepatitis in 5% to 15% of patients and progression to cirrhosis in 2% to 6% annually. Follow-up of patients beginning at the early phase of infection might provide data with less referral bias than in previous studies. METHODS: Test of liver biochemistry, assessment of virological markers, and ultrasound examinations were performed at regular intervals during the course of hepatitis B e antigen (HBeAg) to antibody (anti-HBe) seroconversion in 240 HBeAg carriers with normal alanine aminotransferase levels at baseline. Factors predictive of cirrhosis were identified by multivariate analysis. RESULTS: We enrolled 130 men and 110 women. The mean (+/- SD) age at entry was 27.6 +/- 6.2 years. During the HBeAg-positive phase, 29% of patients had alanine aminotransferase levels > or =200 U/L, 3% had bilirubin levels > or =2.0 mg/dL, and 5% had two or more episodes of alanine aminotransferase levels > or =200 U/L. The mean age at anti-HBe seroconversion was 31.3 +/- 7.0 years, with remission of hepatitis in all patients. However, hepatitis recurred in 36 patients (15%), with an annual rate of 2.2%. Thirteen patients (5%) progressed to cirrhosis. The annual incidence of cirrhosis was 0.5%, and the cumulative probability of cirrhosis after 17 years was 12.6%. Age at anti-HBe seroconversion and relapse of hepatitis were independent risk factors for cirrhosis. CONCLUSION: The clinical severity of chronic hepatitis B was milder in this cohort than in previous studies. Delayed HBeAg seroconversion and relapse of hepatitis were associated with increased risk of cirrhosis.

Adolescent↗

PubMed2005

Persistent normalization of serum alanine aminotransferase levels improves the prognosis of type 1 autoimmune hepatitis.

BACKGROUND/AIMS: Autoimmune hepatitis shows a good response to immunosuppressive treatment, and the prognosis may be determined by the clinical course. The present study was conducted in order to analyze the factors contributing to the outcomes of patients with type 1 autoimmune hepatitis. METHODS: Eighty-four consecutive patients with type 1 autoimmune hepatitis were followed up regularly for a median follow-up period of 70.5 months (16.2-163 months). We analyzed the prognostic factors using time-fixed and time-dependent Cox proportional hazard models. The end point was progression of the disease to decompensated liver cirrhosis. RESULTS: Seventy-seven patients (92%) were treated with prednisolone during the follow-up period, and 11 patients (13%) developed decompensated liver cirrhosis. Using a time-dependent multivariate model, the starting dose of corticosteroid (dose of prednisolone <20 mg/day), relapse within 3 months after the normalization of serum alanine aminotransferase levels with initial treatment, and elevated serum alanine aminotransferase levels during the follow-up period (>40 IU/L), all showed a significant association with progression of the disease. CONCLUSIONS: The prognosis of type 1 autoimmune hepatitis on adequate immunosuppressive treatment improves when the serum alanine aminotransferase level persists at < or = 40 IU/L. Factors existing prior to medical treatment may not affect the prognosis.

Adolescent↗

PubMed2000

Utility of alpha-glutathione S-transferase assessment in chronic hepatitis C patients with near normal alanine aminotransferase levels.

OBJECTIVES: To study whether determining alpha-glutathione S-transferase (alpha-GST) might improve the assessment of chronic hepatitis C (CHC) patients with near normal alanine aminotransferase levels (NNA). DESIGN AND METHODS: We studied 119 viraemic CHC patients. They were subdivided into two groups according to the pattern of alanine aminotransferase (ALT) alteration, i.e. consistently above (HA) or below (NNA) twice the upper normal value. In these patients we assessed alpha-GST and correlated its levels to clinical, histological, and virological findings, further evaluating whether alpha-GST might improve the assessment of CHC patients with NNA. RESULTS: alpha-GST showed a significant correlation with aminotransferases, though not with histological necroinflammatory activity and fibrosis or with hepatitis C virus RNA levels. Twenty-seven patients had NNA (23%), and within this subgroup of patients alpha-GST identified a subset of patients with a higher viral load. CONCLUSIONS: alpha-GST in CHC patients is related to hepatocellular necrosis parameters, but unrelated both to histology and to viraemia. However, in patients with NNA, alpha-GST identified a subgroup of patients with a higher viral load. In this subgroup of patients alpha-GST alteration likely represents the expression of a more severe damage. Because this injury is not detectable by the usual biochemical or histological work-up, we suggest that alpha-GST could a useful tool for monitoring liver damage over time.

Adult↗

PubMed2002

Comparative characterization of Aedes 3-hydroxykynurenine transaminase/alanine glyoxylate transaminase and Drosophila serine pyruvate aminotransferase.

This study describes the comparative analysis of two insect recombinant aminotransferases, Aedes aegypti 3-hydroxykynurenine (3-HK) transaminase/alanine glyoxylate aminotransferase (Ae-HKT/AGT) and Drosophila melanogaster serine pyruvate aminotransferase (Dm-Spat), which share 52% identity in their amino acid sequences. Both enzymes showed AGT activity. In addition, Ae-HKT/AGT is also able to catalyze the transamination of 3-HK or kynurenine with glyoxylate, pyruvate or oxaloacetate as the amino acceptor. Kinetic analysis and other data suggest that Ae-HKT/AGT plays a critical role in mosquito tryptophan catabolism by detoxifying 3-HK and that Dm-Spat is primarily involved in glyoxylate detoxification.

Aedes↗

PubMed1999

Synechococcus mutants resistant to an enamine mechanism inhibitor of glutamate-1-semialdehyde aminotransferase.

An enamine mechanism-based inactivator of mammalian delta-aminobutyric acid aminotransferase, 4-amino 5-fluoropentanoic acid is a potent inhibitor of cell growth and pigment formation in the cyanobacterium Synechococcus PCC 6301. It was demonstrated that 4-amino 5-fluoropentanoic acid inhibits the aminolaevulinate synthesis at glutamate 1-semialdehyde aminotransferase and that in the mutant obtained by exposing cells to 40 microM 4-amino 5-fluoropentanoic acid, this enzyme was insensitive to the inhibitor. The specific activity of glutamate 1-semialdehyde aminotransferase in cell extracts was lower in the mutant, although the cell growth rate was unaffected. The decrease in sensitivity to 4-amino 5-fluoropentanoic acid in the mutant is due to a structural gene mutation, a single base change in the hemL gene resulting in a S162T substitution in the gene product.

Aminolevulinic Acid↗