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)

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

The content of free amino acids, activity of aspartate and alanine transaminase, number of sulphydryl groups in fish tissues were studied as affected by lethal amounts (3.2 g/l) of blue-green algae. Blue-green algae have a certain affect on fishes not only by excreting biologically active substances in the process of vital activity and decay but also changing the gas regime of the medium (the oxygen content lowers, the amount of carbon dioxide increases). Under the algae effect the total content of free amino acids in the fish liver, intestine and muscles increases, mainly due to a rise in the content of glutamic acid with threonine and aspartic acid with serine. These changes are most essential in the liver, intestine and are less pronounced in the muscles. Under the effect of blue-green algae the activity of aspartate transaminase increases in the heart, brain and decreases in the intestine. The activity of alanine transaminase enhances in the heart, intestine and brain. The ration value for these enzymes changes significantly in the brain, liver, intestine, but does not differ from the control in the muscles.
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PMID:[Amino acid composition and transaminase activity in fish tissues, in a medium containing Cyanophyceae]. 10 39

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

A method for the purification of two cysteinesulphinate transaminases, A and B (EC 2.6.1), is described. These enzymes catalyse the conversion of cysteinesulphinic acid to beta-sulphinyl pyruvate. The final preparations are homogeneous by polyacrylamide gel electrophoresis, sodium dodecyl sulphate-polyacrylamide gel electrophoresis and isoelectrofocusing. The molecular weight of the subunits is 41 000 for cysteinesulphinate transaminase A and 43 400 for B. Both enzymes are unspecific, as L-asparate, L-glutamate and L-cysteic acid serve as substrates in addition to L-cysteinesulphinic acid. Cysteinesulphinate transaminase A has a Km of 9.8 mM for cysteinesulphinic acid and 0.25 mM for aspartic acid, whereas the B enzyme has a Km of 6.5 mM for cysteinesulphinic acid and 1.4 mM for aspartic acid. The Vmax values of the A and B enzymes are respectively 7.1 and 6.2 mmol h-1 mg-1 protein for aspartic acid and 45 and 9.3 mmol h-1 mg-1 protein for cysteinesulphinic acid. Both enzymes exhibit maximum activity at pH 8.6. A high specific activity is found in optimal conditions for these two transaminases, the pI values being 9.06 and 5.70 for cysteinesulphinate transaminase A and B respectively. These results have been compared with those already obtained for purified aspartate aminotransferase. Similarities in the pathways of taurine and gamma-aminobutyric acid (GABA) metabolism are discussed.
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PMID:Similarities between cysteinesulphinate transaminase and aspartate aminotransferase. 26 60

Cysteine aminotransferase has been purified over 300-fold from rat liver mitochondria. Transamination between L-cysteine and 2-oxoglutarate, and the reverse reaction, were observed to be catalyzed by the purified enzyme but inhibited by L-aspartate. The enzyme also catalyzed transamination of alanine, 3-sulfinic acid, aspartic acid, and cysteic acid. A new reaction assay method was devised, contributing an indication that mitochondrial cysteine aminotransferase is identical to mitochondrial aspartate aminotransferase. The latter apparently catalyzed 3 transamination reactions in the cysteine degradation process within mitochondria.
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PMID:Purification and characterization of mitochondrial cysteine aminotransferase from rat liver. 75 89

Glutamate aspartate transaminase (EC 2.6.1.1) is a dimeric enzyme with identical subunits with each active site containing pyridoxal 5'-phosphate linked via an internal Shiff's base to a lysine residue. It is not known if these sites interact during catalysis but negative cooperativity has been reported for binding of the coenzyme (Arrio-Dupont, M. (1972), Eur. J. Biochem. 30, 307). Also nonequivalence of its subunits in binding 8-anilinonaphthalene-1-sulfonate (Harris, H.E., and Bayley, P. M. (1975), Biochem. J. 145, 125), in modification of only a single tyrosine with full loss of activity (Christen, P., and Riordan, J.F. (1970), Biochemistry 9, 3025), and following modification with 5,5'-dithiobis(2-nitrobenzoic acid) (Cournil, I., and Arrio-Dupont, M. (1973), Biochemie 55, 103) has been reported. However, steady-state and transient kinetic methods as well as direct titration of the active site chromophore with substrates and substrate analogs have not revealed any cooperative phenomena (Braunstein, A. E. (1973), Enzymes, 3rd Ed. 9, 379). It was therefore decided that a more direct approach should be used to clarify the quistion of subunit interaction during the covalent phase of catalysis. To this end a hybrid method was devised in which a hybrid transaminase was prepared which contained one subunit with a functional active site while the other subunit has the internal Shiff's base reduced with NaBH4. The specific activities and amount of "actively bound" pyridoxal 5'-phosphate are both in a 2:1 ratio for the native and hybrid forms. Comparison of the steady-state kinetic properties of the hybrid and native enzyme forms shows that both forms gave parallel double reciprocal plots which is characteristic of the Ping-Pong Bi-Bi mechanism of transamination. The Km values for the substrates L-aspartic acid and alpha-ketoglutaric acid are nearly identical while the Vmax value for the hybrid is one-half the value of the native transaminase. It therefore appears that the active sites of glutamate aspartate transaminase function independently and a compulsory flip-flop mechanism is not involved.
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PMID:Hybridization of glutamate aspartate transaminase. Investigation of subunit interaction. 117 14

Cytotoxic T lymphocyte (CTL)-mediated cytolysis is induced via the interaction of the specific T-cell antigen receptor and the peptidic viral antigen associated with the major histocompatibility complex class I antigen. Here we demonstrate in vitro that lymphocytic choriomeningitis virus (LCMV) can escape the cytotoxic activity of LCMV-specific cloned CTLs by single amino acid changes within the recognized T-cell epitope defined by residues 275-289 of the LCMV glycoprotein [LCMV-GP-(275-289)]. LCMV-infected fibroblasts at a multiplicity of infection of 10(-3) exposed to virus-specific CTL at an effector-to-target cell ratio of 4:1 4 hr after infection was optimal for virus mutant selection. The selections were carried out with three LCMV-GP-(275-289)-specific CTL clones expressing T-cell antigen receptors containing the identical variable gene segments V alpha 4 and V beta 10 but different junctional regions; selection was also possible with LCMV-GP-(275-289)-specific cytotoxic polyclonal T cells. The most common escape mutation was an amino acid change of asparagine (AAT) to aspartic acid (GAT) at position 280; an additional mutation was glycine (GGT) to aspartic acid (GAT) at position 282. The results presented show that relevant point mutations within the T-cell epitope of LCMV-GP-(275-289) occur frequently and that they are selectable in vitro by CTLs.
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PMID:In vitro selection of lymphocytic choriomeningitis virus escape mutants by cytotoxic T lymphocytes. 172 16

Photometric-kinetic methods for the determination of activity of aspartate aminotransferase are proposed. The flow-injection manifold used for this purpose includes a selecting valve which allows the sample to be trapped in a closed circuit where a solid reactor housing an auxiliary enzyme and a conventional single detector allows a multipeak recording to be obtained for each sample. This record represents a typical kinetic curve from which much information can be obtained to develop fixed-time and reaction-rate methods for the determination of the analyte based on its catalytic action on the L-aspartic acid-2 oxoglutarate system. The linear range is found to be between 1 and 500 U l-1, with relative standard deviation less than 1%. The utility of the methods is illustrated by the determination of the analyte in human serum from healthy and sick individuals.
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PMID:Kinetic determination of aspartate aminotransferase in human serum with a flow-injection/multidetection system. 182 Nov 42

[3H]Glutamate uptake into astrocytes in primary culture was potently inhibited by the aspartate analogues L- and D-aspartic acid, DL-threo-beta-hydroxy-aspartic acid-beta-hydroxymate (IC50's: 136, 259, 168, and 560 microM, respectively) and by beta-DL-methylene-aspartate, a suicide inhibitor of aspartate aminotransferase (IC50: 524 microM), and by the endogenous sulphur-containing amino acid L-cysteinesulfinic acid (IC50: 114 microM), [3H]Glutamate uptake was not significantly affected by either N-methyl-D-aspartate or DL-homocysteine thiolactone. These results demonstrate that other excitatory amino acids including aspartate and L-cysteinesulfinic acid (but excluding L-homocysteic acid) interact with the glutamate transport system of astrocytes. Inhibition of glutamate uptake may significantly increase the level of neuronal excitability.
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PMID:Beta-DL-methylene-aspartate, an inhibitor of aspartate aminotransferase, potently inhibits L-glutamate uptake into astrocytes. 257 Oct 95

In experiments on 6 sheep the authors found the following enzyme activities in bacteria in the rumen fluid, bacteria adhering to the epithelium of the rumen wall and bacteria adhering to food particles in the rumen (given in nkat X g-1 bacterial dry weight): GDH (NADH): 725 +/- 165, 558 +/- 127, 661 +/- 153; GDH (NADPH): 558 +/- 338, 255 +/- 88, 565 +/- 139; GOAT (NADH): 46 +/- 23, 67 +/- 31, 66 +/- 14; GOGAT/NADPH: 58 +/- 27, 56 +/- 15, 65 +/- 29; GS: 153 +/- 65, 69 +/- 35, 71 +/- 32; ALT: 71 +/- 25, 43 +/- 20, 52 +/- 11; AST: 52 +/- 12, 33 +/- 16, 28 +/- 15. The results show that, except for GDH (NADPH), there were no significant differences between the given enzyme activities in the rumen fluid and in bacteria adhering to the rumen wall and to food. Adherent rumen bacteria have the same potential possibilities as the rumen fluid bacteria for the utilization of ammonia, particularly for the synthesis of glutamic acid, glutamine, alanine and aspartic acid, with the above enzymes as catalysts. By means of the GS/GOGAT system, adherent rumen bacteria can probably synthesize glutamic acid in the presence of a limited NH3 concentration in the rumen.
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PMID:Ammonia-utilizing enzymes of adherent bacteria in the sheep's rumen. 286 70


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