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PubMed1990

Structure of the genes of two homologous intracellularly heterotopic isoenzymes. Cytosolic and mitochondrial aspartate aminotransferase of chicken.

The genes of mitochondrial and cytosolic aspartate aminotransferase of chicken were cloned and sequenced. In both genes nine exons encode the mature enzyme. The additional exon for the N-terminal presequence that directs mitochondrial aspartate aminotransferase into the mitochondria is separated by the largest intron from the rest of the gene. A comparison of the two genes of chicken with the aspartate aminotransferase genes of mouse [Tsuzuki, T., Obaru, K., Setoyama, C. & Shimada, K. (1987) J. Mol. Biol. 198, 21-31; Obaru, K., Tsuzuki, T., Setoyama, C. & Shimada, K. (1988) J. Mol. Biol. 200, 13-22] reveals closely similar structures: in the gene of both the mitochondrial and the cytosolic isoenzyme all but one intron positions are conserved in the two species and five introns out of nine are placed at the same positions in all four genes indicating that the introns were in place before the genes of the two isoenzymes diverged. The variant consensus sequence (T/C)11 T(C/T)AG at the 3' splice site of the introns of the genes for nuclear-encoded mitochondrial proteins, which had been deduced from a total of 34 introns [Juretić, N., Jaussi, R., Mattes, U. & Christen, P. (1987) Nucleic Acids Res. 15, 10,083-10,086], was confirmed by including an additional 22 introns into the comparison. The position -4 at the 3' splice site is occupied by base T in 43% of the total 56 introns and appears to be subject to a special evolutionary constraint in this particular group of genes. The following course of evolution of the aspartate aminotransferase genes is proposed. Originating from a common ancestor, the genes of the two isoenzymes intermediarily evolved in separate lineages, i.e. the ancestor eukaryotic and ancestor endosymbiontic cells. When endosymbiosis was established, part of the endosymbiontic genome, including the aspartate aminotransferase gene, was transferred to the nucleus. This process probably led to the conservation of certain splicing factors specific for nuclear-encoded mitochondrial proteins. The presequence for the mitochondrial isoenzyme was acquired by DNA rearrangement. In the eukaryotic lineage, the mitochondrial isoenzyme evolved more slowly than its cytosolic counterpart.

Amino Acid Sequence↗

PubMed1976

Purification, characterization and identification of tryptophan aminotransferase from rat brain.

Tryptophan aminotransferase was purified from rat brain extracts. The purified enzyme had an isoelectric point at pH 6.2 and a pH optimum near 8.0. On electrophoresis the enzyme migrated to the anode. The enzyme was active with oxaloacetate or 2-oxoglutarate as amino acceptor but not with pyruvate, and utilized various L-amino acids as amino donors. With 2-oxoglutarate, the order of effectiveness of the L-amino acids was aspartate >> 5-hydroxytryptophan > tryptophan > tyrosine > phenylalanine. Aminotransferase activity of the enzyme towards tryptophan was inhibited by L-glutamate. Sucrose density gradient centrifugation gave a molecular weight of approx. 55,000. The enzyme was present in both the cytosol and synaptosomal cytosol, but not in the mitochondria. The isoelectric focusing profile of tryptophan: oxaloacetate aminotransferase activity was identical with that of L-aspartate: 2-oxoglutarate aminotransferase (EC 2.6.1.1) activity, with both subcellular fractions. On the basis of these data, it is suggested that the enzyme is identical with the cytosol aspartate: 2-oxoglutarate aminotransferase.

Animals↗

PubMed2006

The prevalence and predictors of elevated serum aminotransferase activity in the United States in 1999-2002.

OBJECTIVES: The presence of elevated serum aminotransferase activity is a sign of possible underlying liver disease. We aimed to describe the prevalence and associations of elevated serum aminotransferase activity in a recent, nationally representative U.S. survey. METHODS: We described the prevalence and predictors of elevated alanine aminotransferase (ALT >43 IU/L) or elevated aspartate aminotransferase (AST >40 IU/L) activity among 6,823 participants of the National Health and Nutrition Examination Survey (NHANES) conducted between 1999 and 2002. We compared our findings to the results already published based on the NHANES conducted between 1988 and 1994. RESULTS: In NHANES 1999-2002, the prevalences of elevated ALT, AST, or either ALT or AST were 8.9%, 4.9%, and 9.8%, respectively, in the entire population and 7.3%, 3.6%, and 8.1%, respectively, after excluding participants who tested positive for hepatitis C virus (HCV) antibody or reported excessive alcohol consumption. Strong predictors of elevated ALT activity included increasing waist circumference and body mass index, alcohol consumption, male sex, Mexican American ethnicity, decreasing age, and presence of HCV antibody. In NHANES 1988-1994, which employed a different assay methodology, the prevalences of elevated aminotransferases were approximately half of the prevalences we describe in NHANES 1999-2002, but the predictors of elevated ALT activity were similar. CONCLUSIONS: The current prevalence of elevated ALT activity in the United States (8.9%) is more than double that of previously available estimates. This prevalence is very high (7.3%) even among persons without viral hepatitis C or excessive alcohol consumption and is strongly associated with risk factors for nonalcoholic fatty liver disease.

Adult↗

PubMed1993

Isolation and characterization of a gene coding for a novel aspartate aminotransferase from Rhizobium meliloti.

Aspartate aminotransferase (AAT) is an important enzyme in aspartate catabolism and biosynthesis and, by converting tricarboxylic acid cycle intermediates to amino acids, AAT is also significant in linking carbon metabolism with nitrogen metabolism. To examine the role of AAT in symbiotic nitrogen fixation further, plasmids encoding three different aminotransferases from Rhizobium meliloti 104A14 were isolated by complementation of an Escherichia coli auxotroph that lacks three aminotransferases. pJA10 contained a gene, aatB, that coded for a previously undescribed AAT, AatB. pJA30 encoded an aromatic aminotransferase, TatA, that had significant AAT activity, and pJA20 encoded a branched-chain aminotransferase designated BatA. Genes for the latter two enzymes, tatA and batA, were previously isolated from R. meliloti. aatB is distinct from but hybridizes to aatA, which codes for AatA, a protein required for symbiotic nitrogen fixation. The DNA sequence of aatB contained an open reading frame that could encode a protein 410 amino acids long and with a monomer molecular mass of 45,100 Da. The amino acid sequence of aatB is unusual, and AatB appears to be a member of a newly described class of AATs. AatB expressed in E. coli has a Km for aspartate of 5.3 mM and a Km for 2-oxoglutarate of 0.87 mM. Its pH optimum is between 8.0 and 8.5. Mutations were constructed in aatB and tatA and transferred to the genome of R. meliloti 104A14. Both mutants were prototrophs and were able to carry out symbiotic nitrogen fixation.

Amino Acid Sequence↗

PubMed1996

Comparison of effect of cafetière and filtered coffee on serum concentrations of liver aminotransferases and lipids: six month randomised controlled trial.

OBJECTIVE: To study the effects of prolonged intake of cafetière coffee, which is rich in the diterpenes cafestol and kahweol, on serum aminotransferase and lipid concentrations. DESIGN: Randomised parallel controlled trial. SUBJECTS: 46 healthy men and women aged 19 to 69. INTERVENTION: Consumption of five to six strong cups (0.9 litres) a day of either cafetière (22 subjects) or filtered coffee (24 subjects) for 24 weeks. MAIN OUTCOME MEASURES: Mean changes in serum aminotransferase and lipid concentrations. RESULTS: Cafetière coffee raised alanine aminotransferase concentration by up to 80% above baseline values relative to filtered coffee. After 24 weeks the rise was still 45% (9 U/l (95% confidence interval 3 to 15 U/l), P = 0.007). Alanine aminotransferase concentration exceeded the upper limit of normal in eight of the 22 subjects drinking cafetière coffee, being twice the upper limit of normal in three of them. Cafetière coffee raised low density lipoprotein cholesterol concentrations by 9-14%. After 24 weeks the rise was 0.26 mmol/l (0.04 to 0.47 mmol/l) (P = 0.03) relative to filtered coffee. Triglyceride concentrations initially rose by 26% with cafetière coffee but returned close to baseline values within six months. All increases were reversible after the intervention was stopped. CONCLUSIONS: Daily consumption of five to six cups of strong cafetière coffee affects the integrity of liver cells as suggested by small increases in serum alanine aminotransferase concentration. The effect does not subside with prolonged intake. High intakes of coffee brews rich in cafestol and kahweol may thus be responsible for unexplained increases in this enzyme activity in apparently healthy subjects. Cafetière coffee also raises low density lipoprotein cholesterol concentration and thus the risk of coronary heart disease.

Adult↗

PubMed2003

Circulating intercellular adhesion molecule-1 in chronic hepatitis C patients with normal or elevated aminotransferase before and after alpha-interferon treatment.

OBJECTIVES: Intercellular adhesion molecule-1 (ICAM-1) plays a fundamental role during liver inflammation. In fact, weak ICAM-1 expression is physiologically restricted to the endothelium of portal vessels and to sinusoidal lining cells, but it becomes markedly evident on sinusoidal lining cells and at the surface of hepatocytes during inflammatory liver diseases. The aim of this study was to evaluate the behaviour of soluble ICAM-1 (sICAM-1) in chronic hepatitis C (CH-C) patients with persistently normal aminotransferase in comparison with patients with CH-C and elevated aminotransferase, and its changes during alpha-interferon (IFN) therapy. Immunohistochemical localization of ICAM-1 was also performed on liver tissue specimens of both groups. METHODS: Sixty subjects were divided into 3 groups: group A included 19 patients with CH-C and persistently normal aminotransferase; group B included 21 patients with CH-C and persistently elevated aminotransferase levels, and group C included 20 healthy subjects representing the control group. The first two groups were treated with recombinant alpha-IFN 2b at a dose of 6 MU 3 times a week for 3 months and followed up with 3 MU 3 times a week for another 3 months. RESULTS: Baseline values of serum ICAM-1 in groups A and B were significantly higher than those in group C (p < 0.0001). The median baseline value of sICAM-1 in group A (525.0 ng/ml) was lower than that of group B (561.0 ng/ml), but the difference was not statistically significant. Furthermore, there was a trend toward higher ICAM-1 values as histological severity increased (Mantel-Haenszel chi(2) 8.8, p < 0.003). Post-treatment sICAM-1 serum values showed a marked decrease in both groups, but only among responder patients, while ICAM-1 levels were unchanged in non-responders. Immunohistochemical localization showed no staining for ICAM-1 in normal liver specimens, while there was a quite similar staining for ICAM-1 in the two groups of patients, consistent with an inflammatory process. CONCLUSIONS: This study shows that circulating ICAM-1 levels in most patients with CH-C and persistently normal aminotransferase are higher than those in a control group and the fact that ICAM-1 molecules are also expressed on the hepatocyte membrane suggests that they could play an important role, in association with other molecules, in the intercellular adhesion processes during the induction and maintenance phases of the immune response. In both groups, only patients responding to alpha-IFN therapy showed a marked decrease in serum ICAM-1 below baseline values.

Adult↗

PubMed2006

Retrospective analysis of transient elevations in alanine aminotransferase during long-term treatment with acetaminophen in osteoarthritis clinical trials.

BACKGROUND: In two recent osteoarthritis trials, alanine aminotransferase (ALT) elevations were observed more frequently in patients receiving acetaminophen 3.9 g daily than in patients receiving placebo, and the rates were higher than aminotransferase values observed in some previous osteoarthritis studies with acetaminophen. OBJECTIVE: To retrospectively analyze ALT data from McNeil osteoarthritis clinical studies involving acetaminophen in order to assess the frequency and magnitude of ALT elevations and rate of ALT resolution while patients remained on acetaminophen treatment. A review of the literature revealed a few reports of isolated aminotransferase elevations occurring during acetaminophen therapy, but these reports were not included in the analysis because they did not include enough information to evaluate the frequency, magnitude, and rate of ALT elevations while patients remained on acetaminophen treatment. RESEARCH DESIGN AND METHODS: Nine controlled clinical trials were identified in which at least one of the treatments was acetaminophen alone. Studies were included if patients had ALT and aspartate aminotransferase (AST) values obtained at baseline and an ALT value at an additional visit after initiating therapy. Seven studies met these criteria and were included in this analysis. In these studies, patients received acetaminophen 1950-4000 mg/day for 4 weeks up to 12 months. Laboratory testing was performed at weeks 0 and 4 in the three 4-week studies; at weeks 0, 2, 4, 8, and 12 in the two 12-week studies; at weeks 0, 1, 2, 4, 6, 8, and 13 in the 13-week study; and at months 0, 1, 3, 6, 9, and 12 in the 12-month study. The pooled data set consisted of patient demographics, dosing records, aminotransferase and bilirubin laboratory values, and adverse events. RESULTS: There were no reports of hepatotoxicity or hepatic failure in any acetaminophen-treated patient (n = 1530). In the seven studies, 1039 patients had both baseline AST and ALT activity < or = upper limit of the reference range and an on-treatment ALT measurement. While on long-term acetaminophen treatment, 181 of 1039 (17.4%) patients had an ALT value that exceeded the upper limit of the reference range. None of the 1039 patients had an on-treatment ALT level > 3 times upper limit of the reference range in conjunction with a serum bilirubin > upper limit of the reference range, and no patient had an ALT level > 10 times upper limit of the reference range. Of the 1039 patients, 44 (4.2%) had an on-treatment ALT level > 1.5 times upper limit of the reference range, and 31 of the 44 patients had a subsequent measurement of ALT. Of these 31 patients, 29 (93.5%) had documented resolution or decreasing ALT while on treatment. An ALT level > 1.5 times upper limit of the reference range was not associated with a higher frequency of symptoms potentially related to hepatic origin. LIMITATIONS: The studies included in this analysis were limited to McNeil studies, none of which were designed to specifically evaluate the patterns of ALT activity. Thus, the incidence of ALT elevations after any specific duration of dosing, and the temporal pattern of ALT elevations, cannot be accurately determined. In addition, methodological differences existed across the studies. CONCLUSION: This analysis involving > 1000 acetaminophen-treated patients shows that low-level, transient ALT elevations usually resolve or decrease with continued acetaminophen treatment, are unaccompanied by signs or symptoms of liver injury, and, as such, appear to be clinically insignificant. Maximum recommended daily doses of acetaminophen did not cause liver failure or dysfunction.

Acetaminophen↗

PubMed1987

Effect of vitamin B6 on the synthesis and degradation of aspartate aminotransferase in chicken embryo fibroblasts.

The effect of pyridoxal depletion and supplementation on the intracellular level of mitochondrial and cytosolic aspartate aminotransferase in cultured chicken embryo fibroblasts was examined. No apoenzyme was detected in cells grown in the presence of pyridoxal, and the specific activity of total enzyme did not vary profoundly from primary to quaternary cultures. Under pyridoxal depletion, up to 40% apoenzyme was found in tertiary cultures which was entirely due to the mitochondrial isoenzyme. Cytosolic apoenzyme was never detected. Total aspartate aminotransferase relative to total protein was increased 2-fold in secondary cultures; only the mitochondrial isoenzyme contributed to the increased specific activity. The cytosolic isoenzyme decreased steadily and was below the limit of detection in quaternary cultures. The changes are attributed to an increased and decreased synthesis of mitochondrial and cytosolic isoenzyme, respectively. No induction of either isoenzyme was observed after incubating the cells with different hormones and substrates. In secondary cultures, no degradation of mitochondrial isoenzyme could be detected under pyridoxal deficiency or supplementation during 4.4 days, an interpassage duration. The cytosolic aspartate aminotransferase was degraded initially with an apparent half-life of approximately 0.9 day under both sets of conditions. The pronounced stability of mitochondrial aspartate aminotransferase, even though one-third of it was present as apoenzyme, excludes the formation of the apoform to be the rate-limiting step in its degradation. The present results show that pyridoxal affects the synthesis of mitochondrial and cytosolic aspartate aminotransferase, but differently.

Animals↗

PubMed1985

Regulation of aminotransferase-glutamate dehydrogenase interactions by carbamyl phosphate synthase-I, Mg2+ plus leucine versus citrate and malate.

Citrate, malate, and high levels of ATP dissociate the mitochondrial aspartate aminotransferase-glutamate dehydrogenase complex and have an inhibitory effect on the latter enzyme. These effects are opposed by Mg2+, leucine, Mg2+ plus ATP, and carbamyl phosphate synthase-I. In addition, Mg2+ directly facilitates formation of a complex between glutamate dehydrogenase and the aminotransferase and displaces the aminotransferase from the inner mitochondrial membrane which could enable it to interact with glutamate dehydrogenase in the matrix. Zn2+ also favors an aminotransferase-glutamate dehydrogenase complex. It, however, is a potent inhibitor of and has a high affinity for glutamate dehydrogenase. Leucine, however, enhances binding of Mg2+ and decreases binding of and the effect of Zn2+ on the enzyme. Thus, since both metal ions enhance enzyme-enzyme interaction and Zn2+ is a more potent inhibitor, the addition of leucine in the presence of both metal ions results in activation of glutamate dehydrogenase without disruption of the enzyme-enzyme complex. Furthermore, the combination of leucine plus Mg2+ produces slightly more activation than leucine alone. These results indicate that leucine, carbamyl phosphate synthase-I, and its substrate and cofactor, ATP and Mg2+, operate synergistically to facilitate glutamate dehydrogenase activity and interaction between this enzyme and the aminotransferase. Alternatively, Krebs cycle intermediates, such as citrate and malate, have opposing effects.

Adenosine Triphosphate↗

PubMed1977

Aspartate aminotransferase of Pediococcus cerevisiae.

A five-step procedure is described for preparing highly purified aspartate aminotransferase (L-aspartate: 2-oxoglutarate aminotransferase, EC.2.6.1.1) from cell-freee enzyme extracts of Pediococcus cerevisiae. An overall purification of 130-fold was achieved. Some of P. cerevisiae aspartate aminotransferase properties were studied, i.s. pH optimum (7.8--8.0), optimum of temperature (37 degrees), Michaelis constans for 4 enzyme substrates and substrate specificity of enzyme. The enzyme is very thermolabile. During purification the enzyme was stabilizated by 2-oxoglutarate. The highly purified preparation was stored in the solution containing ammonium sulphate. The obtained aspartate aminotransferase preparation was free of alanine and aromatic amino acids aminotransferase activites and did not reveal malate dehydrogenase activity.

Aspartate Aminotransferases↗

PubMedDate not supplied

[Effect of pyridoxal phosphate on the activity of aminotransferases in different structure-functional regions of the rabbit brain in radiation sickness].

Pyridoxal enzymes of transamination (aspartate aminotransferase, KF 2.6.1.1. and alanine aminotransferase, KF 2.6.1.2) have been studied for their activity in different departments of the rabbit brain under the effect of ionizing radiation and introduction of pyridoxal phosphate. It has been established that the effect of ionizing radiations does not evoke the change in aspartate aminotransferase and alanine aminotransferase activity in different structure-functional departments of the rabbit brain, the decrease of aminotransferases activity in the acute period of the radiation sickness being natural. Introduction of pyridoxal phosphate irradiated animals promotes relative normalization of activity of the enzymes under study.

Alanine Transaminase↗

PubMed1996

Correlation between the severity of acute hepatic necrosis induced by acetaminophen and serum aminotransferase levels in fasted and sucrose-fed rats.

The relationship between serum aminotransferase levels and the acute hepatic necrosis induced by acetaminophen was studied in 24 male Wistar rats (220-265 g). The animals were divided into two groups, one of which was fasted for 66 h (group I) while the other was fed only sucrose cubes ad libitum (group II). The animals received I g acetaminophen per kg body weight 42 h after the onset of the experiment. Twenty-four hours later, blood was drawn to measure aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels and the liver was removed for both macro- and microscopic examination. The intensity of the hepatic necrosis was scored according to the extent of the lesion. The hepatic necrosis was more frequent and intense in group I, with the aminotransferase levels being higher in this group (median AST and ALT levels were 3900 IU/l and 2511 IU/l, respectively, for group I and 119 IU/l and 79 IU/l, respectively, for group II). There was a positive correlation (rs) between the intensity of hepatic necrosis assessed microscopically and the levels of AST (group I, rs = 0.83; group II, rs = 0.79) and ALT (group I, rs = 0.58; group II, rs = 0.80). These findings suggest that aminotransferase levels are a reliable indicator of the degree of hepatic necrosis in this model of acetaminophen intoxication.

Acetaminophen↗

PubMed1997

Virological response to interferon treatment in hepatitis C virus carriers with normal aminotransferase levels and chronic hepatitis.

Hepatitis C virus (HCV) carriers with normal aminotransferase levels often show histological chronic hepatitis. This study was undertaken to determine the effect of interferon (IFN) in such patients. Nineteen HCV carriers with normal aminotransferase activities and chronic hepatitis were randomized to receive IFN-alpha2b (3 million units 3 times weekly for 12 months) or no treatment. Therapy was monitored by qualitative and quantitative determination of viral RNA. Patients who did not clear HCV RNA after 6 months discontinued therapy. In all, 9 patients constituted the control group, while 10 patients were treated. Five of these patients, still viremic after 6 months, stopped IFN. The remaining 5 patients, who cleared the viral RNA within 6 months, completed the 12-month course. Three of these patients relapsed off treatment, and 2 were still free of viremia 12 months after stopping therapy. A transient flare-up of aminotransferase activities was detected in 2 patients during treatment and in 3 patients after. None of the 9 control patients cleared the viral RNA during follow-up. A variable degree of sequence heterogeneity was detected in the hypervariable region before therapy, and IFN treatment decreased sequence diversity in all patients. These results indicate that IFN therapy can be effective in chronic HCV carriers with normal aminotransferase activities, inducing short-term virological response in 3 of 10 patients and sustained response in 2. The effects of treatment on viral load and quasispecies complexity were similar to those reported previously in patients with increased aminotransferase activities.

Adult↗

PubMed1983

Possible involvement of cGMP in the control of tyrosine aminotransferase degradation in rat hepatocytes.

Addition of theophylline to primary cultures of rat hepatocytes in which tyrosine aminotransferase had been preinduced with dexamethasone caused a further increase in specific activity of the enzyme. This increase was due in part to a reduction in the rate of tyrosine aminotransferase degradation that began about 2 hr after theophylline was added. The level of cGMP also increased with a similar time lag following the addition of theophylline. The concentration of theophylline which produced the above effects (1 mM) did not alter the rate of general protein degradation in hepatocytes. Addition of 8-bromo-cGMP (0.5 mM) resulted in an immediate reduction in the rate of tyrosine aminotransferase degradation and in an increase in the activity of the enzyme. Treating hepatocytes with MnCl2 (0.9 mM) caused an elevation of cGMP and a concomitant slowing of tyrosine aminotransferase degradation without changing the level of cAMP significantly. These results suggest an inverse relationship between the level of cGMP and the rate of tyrosine aminotransferase degradation in hepatocytes.

Animals↗

PubMed1978

Genetic variation in the activity of the histidine catabolic enzymes between inbred strains of mice: a structural locus for a cytosol histidine aminotransferase isozyme (Hat-1).

Variation in activity of the main histidine catabolic enzymes (histidase, urocanase, and aminotransferase) has been surveyed using inbred strains of mice (C57BL, DBA, Peru, SM, and SWR). Some variation was found in the activity of all enzymes, but only in the case of cytosolic histidine aminotransferase was it greater than twofold (SM 3.3-fold greater than C57BL). The divergent strains for the activity of this enzyme were crossed and the F1's were backcrossed; the segregation analysis indicated a single locus with additively acting alleles (designated Hat-1: a allele SM, b allele C57BL). Cytosolic histidine aminotransferase differed in heat stability between SM and C57BL, indicating that Hat-1 is a structural locus. The conflict in the biochemical literature (Morris et al., 1973; Noguchi et al., 1976a,b) over the number and subcellular distribution of the histidine aminotransferase isozymes is partly resolved by the acquisition of a variant at the Hat-1 locus. Hat-1 affects the cytosolic form but not the mitochondrial form of the enzyme. Purification and analysis of the isozymes of histidine aminotransferase from livers of C57BL and SM mice will further clarify the situation.

Animals↗

PubMed1978

Distribution and tissue specificity of 4-aminobutyrate-2-oxoglutarate aminotransferase.

A rapid and specific method for assaying 4-aminobutyrate-2-oxoglutarate aminotransferase was developed. The method was based on the selectivity of ion exchange resin and the speed of vacuum filtration. With this new method, the aminotransferase activity in various tissues has been determined as follows: brain, 10.2; spinal cord, 11.8; liver, 5.7; kidney, 4.6; heart, 0.5; lung, 0.4 nmol glutamate formed/min/mg. No activity could be detected in muscle preparations. When the aminotransferases were tested with the antibody against the purified 4-aminobutyrate aminotransferase from brain, no difference could be detected among brain, spinal cord, and kidney preparations as judged from the results of immunodiffusion, inhibition of enzyme activity by antibody, and microcomplement fixation. It is concluded that 4-aminobutyrate aminotransferases from various tissues of the mouse are probably identical or closely related.

4-Aminobutyrate Transaminase↗

PubMed2005

Characterization of the oat1 gene of Penicillium chrysogenum encoding an omega-aminotransferase: induction by L-lysine, L-ornithine and L-arginine and repression by ammonium.

The Penicillium chrysogenum oat1 gene, which encodes a class III omega-aminotransferase, was cloned and characterized. This enzyme converts lysine into 2-aminoadipic semialdehyde, and plays an important role in the biosynthesis of 2-aminoadipic acid, a precursor of penicillin and other beta-lactam antibiotics. The enzyme is related to ornithine-5-aminotransferases and to the lysine-6-aminotransferases encoded by the lat genes found in bacterial cephamycin gene clusters. Expression of oat1 is induced by lysine, ornithine and arginine, and repressed by ammonium ions. AreA-binding GATA and GATT sequences involved in regulation by ammonium, and an 8-bp direct repeat associated with arginine induction in Emericella (Aspergillus nidulans and Saccharomyces cerevisiae, were found in the oat1 promoter region. Deletion of the oat1 gene resulted in the loss of omega-aminotransferase activity. The null mutants were unable to grow on ornithine or arginine as sole nitrogen sources and showed reduced growth on lysine. Complementation of the null mutant with the oat1 gene restored normal levels of omega-aminotransferase activity and the ability to grow on ornithine, arginine and lysine. The role of the oat1 gene in the biosynthesis of 2-aminoadipic acid is discussed.

2-Aminoadipic Acid↗

PubMed1986

Insulin enhances transcription of the tyrosine aminotransferase gene in rat liver.

The mechanism of insulin-mediated induction of tyrosine aminotransferase in rat liver was investigated using a cloned cDNA probe. The level of aminotransferase mRNA increases about fourfold following administration of the hormone. This induced mRNA accumulation does not require de novo protein synthesis. Nuclear runoff transcription assays in isolated liver nuclei demonstrate that insulin has a rapid and time-dependent stimulatory effect on aminotransferase gene transcription. The magnitude of enhanced transcription can fully account for the increase in the mRNA. We conclude that the induction of tyrosine aminotransferase in rat liver by insulin is primarily a consequence of a selective increase in the rate of transcription of the aminotransferase gene.

Animals↗