Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.6.1.1 (aspartate aminotransferase)
21,665 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Mutants of Escherichia coli K-12 that require L-tryptophan (trp) are normally unable to utilize D-tryptophan to fulfill their requirement. However, secondary mutations (dadR) that confer this ability can be isolated. In such strains two distinct enzymes are found to be produced at high levels: D-amino acid oxidase (EC 1.4.3.3) and D-tryptophan oxidase. A convenient assay procedure for D-tryptophan oxidase is described. The two enzymes could be distinguished on the basis of their sensitivity to inhibition by L-phenylalanine and L-tyrosine. Strains that were trp dadR could not grow with D-tryptophan in the presence of L-phenylalanine, but further mutations, Fyo, could be isolated that allowed growth under these conditions. Some of them were characterized by further increases in the level of D-tryptophan oxidase activity and a sharp decrease in D-amino acid oxidase. These kinds of Fyo mutations lay in or near the dadR gene. The substrate specificity of the two enzymes toward a large number of compounds was examined. The transamination of aromatic keto acids was investigated. In the wild-type strain only a single enzyme, transaminase A (EC 2.6.1.5), was found, and it was irreversibly activated when subjected to elevated temperatures. The present state of our knowledge on D-amino acid utilization in E. coli is summarized.
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PMID:Role of D-tryptophan oxidase in D-tryptophan utilization by Escherichia coli. 0 93

Two new mutations are described which, together, eliminate essentially all the aminotransferase activity required for de novo biosynthesis of tyrosine, phenylalanine, and aspartic acid in a K-12 strain of Escherichia coli. One mutation, designated tyrB, lies at about 80 min on the E. coli map and inactivates the "tyrosine-repressible" tyrosine/phenylalanine aminotransferase. The second mutation, aspC, maps at about 20 min and inactivates a nonrespressible aspartate aminotransferase that also has activity on the aromatic amino acids. In ilvE- strains, which lack the branched-chain amino acid aminotransferase, the presence of either the tyrosine-repressible aminotransferase or the aspartate aminotransferase is sufficient for growth in the absence of exogenous tyrosine, phenylalanine, or aspartate; the tyrosine-repressible enzyme is also active in leucine biosynthesis. The ilvE gene product alone can reverse a phenylalanine requirement. Biochemical studies on extracts of strains carrying combinations of these aminotransferase mutations confirm the existence of two distinct enzymes with overlapping specificities for the alpha-keto acid analogues of tyrosine, phenylalanine, and aspartate. These enzymes can be distinguished by electrophoretic mobilities, by kinetic parameters using various substrates, and by a difference in tyrosine repressibility. In extracts of an ilvE- tyrB- aspC- triple mutant, no aminotransferase activity for the alpha-keto acids of tyrosine, phenylalanine, or aspartate could be detected.
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PMID:Escherichia coli mutants deficient in the aspartate and aromatic amino acid aminotransferases. 1 83

Two aminotransferases from Escherichia coli were purified to homogeneity by the criterion of gel electrophoresis. The first (enzyme A) is active on L-aspartic acid, L-tyrosine, L-phenylalanine, and L-tryptophan; the second (enzyme B) is active on the aromatic amiono acids. Enzyme A is identical in substrate specificity with transaminase A and is mainly an aspartate aminotransferase; enzyme B has never been described before and is an aromatic amino acid aminotransferase. The two enzymes are different in the Vmax and Km values with their common substrates and pyridoxal phosphate, in heat stability (enzyme A being heat-stable and enzyme B being heat-labile at 55 degrees) and in pH optima with the amino acid substrates. They are similar in their amino acid composition, each enzyme appears to consist of two subunits, and enzyme B may be converted to enzyme A by controlled proteolysis with subtilsin. The conversion was detected by the generation of new aspartate aminotransferase activity from enzyme B and was further verified by identification by acrylamide gel electrophoresis of the newly formed enzyme A. The two enzymes appear to be products of two genes different in a small, probably terminal, nucleotide sequence.
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PMID:Multispecific aspartate and aromatic amino acid aminotransferases in Escherichia coli. 23 11

Escherichia coli aspartate aminotransferase was exposed to aspartate or phenylalanine without oxo acid in buffered 2H2O. The alpha-hydrogen of the amino acids underwent first-order exchange with respect to both substrate and enzyme. P.m.r. spectroscopy gave consistent reaction-rate constants. The deuterium-exchange rate was only moderately increased by addition of oxo acids and was of the same order as the transamination rate. No beta-deuteration was observed. The C(alpha)-H-bond-breaking step is discussed as a part of the entire transamination mechanism.
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PMID:Kinetic studies with the use of proton-magnetic-resonance spectroscopy of the specific alpha-deuteration of amino acids by Escherichia coli aspartate aminotransferase. 35 42

Transaminase B (branched-chain amino acid aminotransferase, EC 2.6.1.42), the ilvE gene product, was purified to apparent homogeneity from an Escherichia coli K-12 strain which carries the ilvE gene both on the host chromosome and on a plasmid. The oligomeric structure of the enzyme, as determined by analytical ultracentrifugation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, was confirmed to be that of a hexamer with a molecular weight of about 182,000 and apparently identical subunits. Cross-linking with dimethylsuberimidate yielded trimers, dimers, and monomers, but essentially no species of higher molecular weight. These results are consistent with a double-trimer arrangement of the subunits in native enzyme. The amino-terminal sequence was found to be: Gly Thr Lys Lys Ala Asp Tyr Ile (Trp) Phe Asn Gly (Thr) (Met) Val. Purified transaminase B catalyzed transamination between alpha-ketoglutarate and l-isoleucine, l-leucine, l-valine, and, to a lesser extent, l-phenylalanine and l-tyrosine, the latter reacting very sluggishly. The enzyme was free of aspartate transaminase and of transaminase C. The apparent K(m) values for the branched-chain alpha-ketoacids were smaller than those for the corresponding amino acids. The lowest K(m) was recorded for dl-alpha-keto-beta-methyl-n-valerate, and the highest was recorded for l-valine. The ratio of the valine- and isoleucine-alpha-ketoglutarate activities did not change significantly during purification, and both activities were quantitatively removed from crude extract by antibody raised against purified transaminase B. These observations argue against the existence of a separate valine-alpha-ketoglutarate transaminase. Anti-E. coli transaminase B antibody cross-reacted with crude extract from Salmonella typhimurium, but not with extract obtained from Pseudomonas aeruginosa.
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PMID:Transaminase B from Escherichia coli: quaternary structure, amino-terminal sequence, substrate specificity, and absence of a separate valine-alpha-ketoglutarate activity. 37 64

Two proteins (form A and form B2) with aromatic-amino-acid aminotransferase activity were detected in extracts of Bacillus subtilis. A histidinol phosphate aminotransferase (protein B1) with aminotransferase activity for the aromatic amino acids was also present. The aspartate aminotransferase (L-aspartate:2-oxoglutarate aminotransferase, EC 2.6.1.1) (protein C) also displayed similar activity. Each of the four proteins was isolated free from the others by the successive application of DEAE-cellulose column chromatography and flat-bed isoelectric focusing at pH range 4-6. Form B2 is the major form of the aromatic-amino-acid aminotransferase (aromatic-amino-acid:2-oxoglutarate amino-transferase, EC 2.6.1.57) and the Km values of tyrosine and phenylalanine with this form are somewhat lower than with the minor form A. The Km of tyrosine with histidinol phosphate aminotransferase (protein B1) is in the same range, but the Km of phenylalanine with this enzyme is 12-20 times higher than the corresponding values with the two forms of the aromatic-amino-acid amino-transferase. Apparent molecular weights were estimated with Sephadex gel filtration to be approx. 73 000, 64 000, 54 000 and 66 000 for form A, form B2, histidinol phosphate aminotransferase and aspartate aminotransferase, respectively. Form B2 is being reported for the first time in this communication.
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PMID:Aminotransferases for aromatic amino acids and aspartate in Bacillus subtilis. 41 16

Photooxidation of a histidine residue in aspartate transaminase leads to proportionate loss of the enzyme activity in reactions with L-aspartate and L-phenylalanine. Modification of two arginine residues by 1,2-cyclohexanedione strongly inhibits transamination of aspartate but, in contrast, slightly increases the rate of phenylalanine transamination. A stimulatory effect of a number of aromatic and aliphatic monocarboxylate anions on the rate of alanine transamination in the active site was observed. Indolylbutyrate was the most effective compound among those tested. Indolylbutyrate and indolylacetate act as competitive inhibitors in the case of transamination of phenylalanine or aspartate. The results were interpreted as indicating the presence in the active center of transaminase of a hydrophobic subsite participating in the binding of aromatic aminoacids.
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PMID:[Effect of chemical modification and carboxylate anions on transamination of phenylalanine and alanine in the active center of chicken cytosol aspartate transaminase]. 56 50

Aspartate transaminase from chicken heart cytosol was immobilized covalently on activated thiol-Sepharose and digested with trypsin. After washing, the thiol-containing peptides were eluted with 2-mercaptoethanol and further purified by gel-filtration and paper chromatography. Three pure cysteinyl peptides were isolated. One of them may be represented as Ile-(Asp, Met, Cys, Gly, Leu, Thr2)-Lys; this peptide is identical to the fragment comprizing residues 387--395 in the peptide chain of aspartate transaminase from pig heart cytosol. It thus contains a cysteine residue homologous to Cys-390 of the pig heart enzyme. The second cysteinyl peptide had the following composition and partial sequence: Tyr-Phe-Val-Ser-Glu-Gly-Phe-Glu-Leu-Phe (Cys, Ala, Glu, Ser2, Phe)Lys, which corresponds to the sequence 242--258 of the pig enzyme and thus contains a cysteine residue homologous to Cys-252. The third cysteinyl peptide was similar to the tryptic peptide of the pig enzyme containing Cys-191.
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PMID:[Thiol peptides from the aspartate transaminase of chicken heart cytosol]. 59 23

It was demonstrated that a combined effect of 20.5-day space flight and gamma-irradiation reduced the content of biologically important amino acids (methionine, phenylalanine, serine, aspartic and glutamic acids) and inhibited the activity of aspartate aminotransferase of sarcoplasmatic proteins in the quadriceps muscle of rats. Comparison of these data with the Cosmos-605 results and literature reports suggested that gamma-irradiation inhibited the synthetic processes in the skeletal muscle.
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PMID:[Effect of space flight and of the accompanying radiation on amino acid metabolism in the skeletal muscle of rats]. 62 8

At least four separate enzymes are found to catalyze the transamination between phenylalanine and alpha-ketoglutarate in E. coli K 12, one of them being the aspartate aminotransferase. The Km of the latter enzyme for alpha-ketoglutarate is 0.3 or 0.035 mM according to the acceptor aminoacid being phenylalanine or aspartate respectively. The double specificity of aspartate aminotransferase in E. coli is however clearly shown by thermal inactivation studies using various effectors or different temperatures, and by the finding of an active transamination between aspartate and phenylpyruvate in the absence of ketoglutarate. This reaction shows the usual ping-pong type of mechanism, which implies that both substances are substrates for the same protein. Contrary to the phenylalanine-alpha-ketoglutarate reaction, which is probably of little importance in vivo when catalyzed by this enzyme, the direct ketoglutarate-free transamination between aspartate and the aromatic alpha-ketoacid is likely to represent a physiological function in regulating, at least partially, the balance between biosynthetic pathways for aromatic aminoacids and aspartate, for instance by maintaining similar ratios between the aminoacid and its ketoacid partner in both cases. For the sake of clarity it is proposed that the name "transaminase A", first devised by Rudman and Meister, be used for aspartate aminotransferase only, knowing that the specificity of this peculiar enzyme behaves as an accessory agent in the transamination of the aromatic compounds.
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PMID:[Transamination of L-aspartate and L-phenylalanine in Escherichia coli K 12]. 76 47


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