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

L-Tyrosine:2-oxoglutarate aminotransferase (EC 2.6.1.5; TAT) and other enzymes that transaminate tyrosine in rat liver cytosol have been separated into four fractions by isoelectric focussing. One of the forms is probably identical to mitochondrial L-aspartate:2-oxoglutarate aminotransferase (EC 2.6.1.1.; mASAT). The other three forms have pI's of 4.72, 4.98 and 5.30 and Km values of 1.3 and 0.3 mM for tyrosine and alpha-ketoglutarate. These heat stable forms have little or no ASAT activity. Rat liver TAT is also separated into three peaks by hydroxylapatite. Each fraction gives only one peak of activity when electrofocussed separately. In the frog, three groups of peaks of TAT activity have been separated by hydroxylapatite column chromatography. The first group is connected with ASAT activity. These peaks (pI's 6.35, 6.50 and 6.90) are heat stable and have a Km value for tyrosine of 4 mM. These fractions probably represent cytoplasmic ASAT (sASAT). The second group of peaks has at least two subforms (pI's 9.0 and 9.4, Km for tyrosine 15 mM). These forms probably represent mASAT. The third group consists of three forms that resemble the major forms of rat liver TAT. These results indicate that heterogeneity is common to many aminotransferases and independent of regulation by glucocorticoids.
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PMID:Heterogeneity of hepatic tyrosine aminotransferase. Separation of the multiple forms from rat and frog liver by isoelectric focussing and hydroxylapatite column chromatography and their partial characterization. 0 12

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

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

DL-alpha-Methyltryptophan (alphaMeTrp), a synthetic analogue of tryptophan, has been found to be a potent inducer of hepatic tyrosine aminotransferase activity in the adrenalectomized rat. alphaMeTrp is inactive in vitro. Unlike the action of other known inducers (tryptophan, hydrocortisone, adenosine cyclic 3:5-monophosphate, and glucagon), maximal stimulation of enzyme activity occurs only 16 to 30 hours after alphaMeTrp administration and the activity is still elevated at 96 hours. Only the L isomer of alphaMeTrp is active, and addition of a hydroxyl group to position 5 of the indole ring renders an inactive compound. The induction can be prevented by actinomycin D or cycloheximide but not galactosamine. Administration of alphaMeTrp together with hydrocortisone produced an additive stimulation of enzyme activity. alphaMeTrp given along with glucagon or adenosine cyclic 3:5-monophosphate caused a further but not additive increase in enzyme activity. Tryptophan given along with alphaMeTrp promoted no extra stimulation whatsoever. These data indicate that alphaMeTrp and tryptophan may act via a common pathway which in part requires RNA synthesis. Other enzymes, namely alanine and aspartate aminotransferase, ornithine aminotransferase, ornithine carbamoyltransferase, serine dehydratase, and histidine ammonialyase, were not affected by treatment of rats with alphaMeTrp.
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PMID:Stimulation of tyrosine aminotransferase activity by dl-alpha-methyltryptophan. 23 76

A convenient method for the purification of aspartate aminotransferase [L-aspartate-2-oxoglutarate aminotransferase (EC 2.6.1.1)] from wheat germ is described. An overall purification of 150 fold was achieved. On polyacrylamide gel electrophoresis at pH 8.9 the purified enzyme revealed two protein bands both provided with enzymatic activity. The holoenzyme is readily resolved on conversion to the aminic form and gel-filtration. The apoenzyme is reactivated by pyridoxal-5-phosphate. Kinetic data indicate that a Ping-Pong mechanism is operative similar to that found for the tyrosine aminotransferase by Litwack and Cleland (1968). Phosphate ion behaves as a competitive inhibitor towards the coenzyme. The relatively low affinity between coenzyme and apoenzyme from wheat germ allowed the determination of the dissociation constants for coenzymes (pyridoxal-5'-phosphate and pyridoxamine-5'-phosphate) and of the inhibition constant for phosphate.
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PMID:Aspartate aminotransferase from wheat germ: purification and kinetic properties. 115 51

Cell-free extracts of epimastigotes of Trypanosoma cruzi contain tyrosine aminotransferase (TAT) and p-hydroxyphenyllactate dehydrogenase (pHPLDH). The TAT activity could be separated from aspartate aminotransferase (ASAT) by polyacrylamide gel electrophoresis or DEAE-cellulose chromatography; the latter procedure also allowed complete separation of pHPLDH. The subcellular localization of both T. cruzi enzymes, as determined by digitonin extraction, subcellular fractionation by differential centrifugation, and isopycnic ultracentrifugation in sucrose gradients, was mainly cytosolic, with low mitochondrial activities.
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PMID:Presence and subcellular localization of tyrosine aminotransferase and p-hydroxyphenyllactate dehydrogenase in epimastigotes of Trypanosoma cruzi. 135 Oct 16

We present a new model for E. coli tyrosine aminotransferase based on the X-ray structures of the wild type and Val39Leu mutant of E. coli aspartate aminotransferase and computer simulation studies. Active site characteristics of the model are correlated with experimental observations on the specificity of these enzymes towards aromatic/dicarboxylic acid substrates.
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PMID:Computational approach towards the three-dimensional structure of E. coli tyrosine aminotransferase. 135 27

The role of DNA methylation in the expression of the rat gamma-glutamyl transpeptidase (GGT) gene was assessed in the Fao cell line using a hypomethylating agent, 5-azacytidine. Ten repetitive treatments of the cells, with 8 microM 5-azacytidine for 24 h, led to 13- and 80-fold increases, respectively, in GGT activity and in GGT mRNA level. The DNA methylation patterns generated by the isoschizomeric restriction enzymes Hpa II and Msp I indicated that the GGT gene, highly methylated in Fao cells, became strongly demethylated after 5-azacytidine treatments. Thus, DNA demethylation increases the expression of the GGT gene. 5-Azacytidine treatments also increased, but to a lesser extent, mRNAs level for actin, albumin, mitochondrial aspartate aminotransferase, aldolase B mRNAs (12- to 16-fold) as well as for tubulin, gluthathione transferase, and tyrosine aminotransferase mRNAs (2- to 5-fold). The GGT gene expression was further studied in B4 cells, cloned from the demethylated Fao cell population. This clone B4 exhibited a stable and strong GGT activity and a highly demethylated GGT gene. Among the three GGT mRNA I, II, or III, transcribed from three different promoters of the single rat GGT gene, only mRNA III was detected in Fao cells and was increased in clone B4, indicating that the demethylation acts on the promoter for mRNA III. The analysis of the differentiation state of B4 cells, as compared to Fao cells, showed a loss of the regulation of GGT and aspartate aminotransferase genes by dexamethasone, as well as a loss of the gluconeogenic pathway. Interestingly, B4 cells have retained many other specific functions of hepatic differentiation and have acquired alpha-fetoprotein expression; thus this clone exhibits the characteristics of a hepatic fetal phenotype.
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PMID:Repetitive 5-azacytidine treatments of Fao cells induce a stable and strong expression of gamma-glutamyl transpeptidase. 138 52


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