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Query: UNIPROT:P17174 (aspartate aminotransferase)
 14,872 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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

A method for the purification of mitochondrial isoenzyme of sheep liver aspartate aminotransferase (EC 2.6.1.1) is described. The final preparation is homogeneous by ultracentrifuge analyses and polyacrylamide-gel electrophoresis and has a high specific activity (182 units/mg). The molecular weight determined by sedimentation equilibrium is 87,100 +/- 680. The amino acid composition is presented; it is similar to that of other mitochondrial isoenzymes, but with a higher content of tyrosine and threonine. Subforms have been detected. On isoelectric focusing a broad band was obtained, with pI 9.14. The properties of the mitochondrial aspartate aminotransferase are compared with those of the cytoplasmic isoenzyme. The Km for L-aspartate and 2-oxoglutarate for the cytoplasmic enzyme were 2.96 +/- 0.20 mM and 0.093 +/- 0.010 mM respectively; the corresponding values for the mitochondrial form were 0.40 +/- 0.12 mM and 0.98 +/- 0.14 mM. Cytoplasmic aspartate aminotransferase showed substrate inhibition by concentrations of 2-oxoglutarate above 0.25 mM in the presence of aspartate up to 2mM. The mitochondrial isoenzyme was not inhibited in this way. Pi at pH 7.4 inhibited cytoplasmic holoenzyme activity by up to about 60% and mitochondrial holoenzyme activity up to 40%. The apparent dissociation constants for pyridoxal 5'-phosphate were 0.23 micrometer (cytoplasmic) and 0.062 micrometer (mitochondrial) and for pyridoxamine 5'-phosphate they were 70 micrometer (cytoplasmic) and 40 micrometer (mitochondrial). Pi competitively inhibited coenzyme binding to the apoenzymes; the inhibition constants at 37 degree C were 32 micrometer for the cytoplasmic isoenzyme and 19.5 micrometer for the mitochondrial form.
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PMID:Some kinetic and other properties of the isoenzymes of aspartate aminotransferase isolated from sheep liver. 3 56

Liver of rat foetuses from 14 to 19 days of gestation and cultured hepatocytes derived from foetuses of 14 or 15 days gestation show a limited capacity to transaminate tyrosine. This low tyrosine transamination activity can be ascribed to aspartate aminotransferase. Definitive tyrosine aminotransferase can be demonstrated in 1-day-old cultures of hepatocytes taken from 19-day foetuses, but not from 15-day foetuses. However, after 3 days of culture hepatocytes from 15-day foetuses are able to synthesize tyrosine aminotransferase. Induction studies reveal that dexamethasone is capable of increasing tyrosine aminotransferase activity once it is detectable in culture.
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PMID:Hepatocyte differentiation in culture. Appearance of tyrosine aminotransferase. 3 44

A middle-aged adult male with a mild form of tyrosinemia II (Richner-Hanhart syndrome) is described. Treatment with a low-tyrosine diet caused a fall in plasma tyrosine and clearing of the hyperkeratosis of the soles. Liver biopsy of this patient revealed low but measurable levels of cytoplasmic tyrosine aminotransferase and elevated levels of the mitochondrial tyrosine-metabolizing enzyme aspartate aminotransferase. It is hypothesized that these enzymes have been induced in sufficient amounts to account for the mild clinical course.
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PMID:Hepatic enzymes of tyrosine metabolism in tyrosinemia II. 4 76

The levels of tyrosine, aspartate and alanine aminotransferases of fetal rat liver were measured and compared with values reported in the literature. Incubation of explants of fetal liver in organ culture resulted in spontaneous increases in tyrosine and alanine aminotransferases, and decrease in aspartate aminotransferase.
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PMID:Activities of tyrosine, alanine and aspartate aminotransferases of fetal rat liver in organ culture. 23 79

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

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

At pH 7, the apoenzyme of carboxymethylated and acylated aspartate aminotransferase reacts selectively with 1,5-difluoro-2,4-dinitrobenzene to form a single intramolecular covalent bond with the epsilon-amino group of the functional lysine residue located within the active centre. On shifting the pH to 9, the second fluorine atom of the bifunctional reagent is substituted with the sterically adjacent side groups of cysteine and tyrosine residues. The modified apoenzyme was subjected to partial proteolysis with pronase, and the digest was used to obtain and isolate the labeled products and to localize amino acid residues involved in the reaction. The established structures of several peptides containing Cys-2,4-dinitrobenzene-Lys and Tyr-2,4-dinitrobenzene-Lys allowed the identification of the amino acid residues involved in the reaction with the bifunctional reagent as Lys 258, Cys 390 and probably Tyr-70. The residues of Cys and Tyr are thus located at a distance of approximately 5 A (the length of the dinitrophenylene bridge) from the lysine residue forming an aldimine bond with pyridoxal 5'-phosphate in the active site.
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PMID:Two-step modification of aspartate aminotransferase with 1,5-difluoro-2,4-dinitrobenzene. Cross-link localization. 66 10

The activity of the aspartate-, alanine-, tyrosine-, phenylalanine- and tryptophane aminotransferases in the rat organes in development have been investigated by quantitative histochemical methods. The isoenzymes have also been examined. The variable increase of the aminotransferase activity has been observed in the liver, brain, heart, skeletal muscle and kidney. In spite of the differences of the aspartate aminotransferase activity in the organs, the increase up to the 7th postnatal day, the reduction after that and the repeated increase after the 14th day reaching the level of the adult animals is evident as a common trend. A considerable increase of the alanine aminotransferase activity has been observed in the late postnatal period. While the difference in the activity of the aromatic aminotransferases in the embryonic organs is small, the changes of the 3 enzymes are different in the postnatal development. The number and the intensity of the isoenzymes of the aspartate- and alanine aminotransferases increase in the development. The isoenzyme spectrum of aromatic aminotransferases in the embryo proves an equal in number and intensity of fractions. In the development this similarity is preserved only with regard to cathode isoenzymes, while with anode once some differences appear.
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PMID:Histochemical evidence of aminotransferases. 82 67


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