Gene/Protein Disease Symptom Drug Enzyme Compound
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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

Biotin deficiency in Aspergillus nidulans resulted in a 70% increase of the protein content and increased levels of free and bound aspartate, glutamate, serine, leucine and methionine. Likewise, the activities of NADP+ glutamate dehydrogenase, NAD+ gluatmate dehydrogenase, aspartate aminotransferase and alanine aminotransferase were significantly increased. The total RNA content increased while the DNA content was unaffected. The rRNA/tRNA ratio remained higher in biotin-deficient cells. Supplementation of glutamate, aspartate, serine, leucine and methionine to the culture medium raised the rRNA/tRNA ratio, and the difference observed in the qualitative and the quantitative patterns of protein and dry cell mass between normal and biotin-deficient cultures was abolished.
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PMID:Factors affecting protein synthesis during biotin deficiency in Aspergillus nidulans. 4 77

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

1. The concentration of HCO3- (independent of any change of pH) exerts different effects on glutamine metabolism in rat kidney-cortex tubules, hepatocytes and enterocytes.2. In kidney tubules HCO3- (10.5-50 MM) has no effect on glutaminase (EC 3.5.1.2), whereas glutamate dehydrogenase (EC 1.4.1.3) is inhibited as HCO3- concentration is increased. The result is that flux through the entire glutamate-to-glucose pathway is inhibited by increasing HCO3- concentrations. A large proportion (more than 30%) of the glutamine removed undergoes complete oxidation. 3. In hepatocytes, and to a smaller extent in enterocytes, HCO3- is an accelerator of glutaminase. Synthesis of glucose and urea from glutamine in hepatocytes increases as HCO3- concentration is increased. Calculations show that fumarate, formed via aspartate aminotransferase and arginino-succinate lyase, is the precursor of the glucose. There is no complete oxidation of the carbon skeleton of glutamine in hepatocytes. 4. Leucine at near-physiological concentrations (0.1-1 mM) is an accelerator of glutaminase in hepatocytes, but not in kidney tubules or in enterocytes. 5. The results are discussed in relation to regulation of acid/base balance in vivo.
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PMID:A role for bicarbonate in the regulation of mammalian glutamine metabolism. 54 52

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

The pyridoxal form of both cytosolic and mitochondrial aspartate aminotransferase is irreversibly inactivated consequent to its interaction with the beta,gamma-unsaturated substrate analogue vinylglycine. Per catalytic cycle, 90% of the enzyme molecules are inactivated while 10% escape inactivation by transamination to the pyridoxamine form. In the presence of vinylglycine plus 2-oxoglutarate, inactivation is complete because of retransamination of the pyridoxamine form to the susceptible pyridoxal form. Peptide analyses after inactivation with [1-14C]vinylglycine showed that vinylglycine alkylates the active-site lysine residue 258 which forms the internal aldimine with the coenzyme pyridoxal 5'-phosphate. The coenzyme itself is left intact; resolution of the inactivated enzyme by base or trichloroacetic acid yields pyridoxal-5'-P. The absorption spectrum of the inactivated enzyme (lambdamax 335 nm) suggests that the cofactor is bound as a substituted aldimine. The proposed pathway of alkylation of Lys-258 involves abstraction of the alpha proton from vinylglycine, isomerization to the alpha,beta-unsaturated enamine, and subsequent nucleophilic attack of the epsilon-amino group of the lysyl residue at the beta carbon of the inhibitor. The determination of the amino acid sequence around the coenzyme-binding lysyl residue in the mitochondrial isoenzyme from chicken gave Ala-(epsilon-Pxy)Lys-Asn-Met-(Gly,Leu,Tyr) which is identical with the other mitochondrial transaminases examined so far.
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PMID:Active-site labeling of aspartate aminotransferases by the beta,gamma-unsaturated amino acid vinylglycine. 91 93

The method for the determination of enzymic activity in turbid, lipaemic sera, which involves clearing by polyanion precipitation with heparin and magnesium chloride, was critically reviewed. In the diagnosis of diseases of the liver and pancreas, which are frequently associated with hyperlipoproteinaemia, only residual enzyme activities are measured in the cleared serum after polyanion treatment. In the measurement of glutamate dehydrogenase and in the Phadebas test for alpha-amylase, the enzymes are inactivated by treatment with heparin and magnesium chloride. On the other hand, as a result of polyanion precipitation gamma-glutamyl transferase is transferred, together with lipoproteins and chylomicrons, to the lipid-rich supernatant. Acid phosphatase also exhibits only residual activity in cleared serum. The activity of aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, leucine arylamidase, cholinesterase, creatine kinase, lactate dehydrogenase, and alpha-hydroxybutyrate dehydrogenase, and the activity of alpha-amylase in the Merckotest are not affected by polyanion treatment of the serum.
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PMID:[Enzyme diagnosis in lipaemic sera before and after polyanion precipitation with heparin and magnesium chloride (author's transl)]. 92 35

The sequences of the coenzyme-binding peptide of both cytoplasmic and mitochondrial aspartate aminotransferases from sheep liver were determined. The holoenzymes were treated with NaBH4 and digested with chymotrypsin; peptides containing bound pyridoxal phosphate were then isolated. One phosphopyridoxyl peptide was obtained from sheep liver cytoplasmic aspartate aminotransferase. Its sequence was Ser-Ne-(phosphopyridoxyl)-Lys-Asn-Phe. This sequence is identical with that reported for the homologous peptide from pig heart cytoplasmic aspartate aminotransferase. Two phosphopyridoxyl peptides with different RF values were isolated from the sheep liver mitochondrial isoenzyme. They had the same N-terminal amino acid and similar amino acid composition. The mitochondrial phosphopyridoxyl peptide of highest yield and purity had the sequence Ala-Ne-(phosphopyridoxyl)-Lys-Asx-Met-Gly-Leu-Tyr. The sequence of the first four amino acids is identical with that already reported for the phosphopyridoxyl tetrapeptide from the pig heart mitochondrial isoenzyme. The heptapeptide found for the sheep liver mitochondrial isoenzyme closely resembles the corresponding sequence taken from the primary structure of the pig heart cytoplasmic aspartate aminotransferase.
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PMID:The sequences of the coenzyme-binding peptide in the cytoplasmic and the mitochondrial aspartate aminotransferases from sheep liver. 118 Aug 94

Untrained rats were subjected to a single intense physical effort. In the plasma the activity of alanine aminotransferase, aspartate aminotransferase, and the concentrations of amino acids: glycine, cystine, alanine and leucine with isoleucine were measured. The results were compared with the data obtained in a control group. Despite lack of statistically significant differences in the activity of aminotransferases and concentration of amino acids between these groups a correlation was found between the activity of AIAT and alanine concentration in the animals after exercise. The concentration of alpha-amino nitrogen was decreased statistically significantly in the group of animals subjected to intensive exercise.
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PMID:The effect of a single intense effort on the activity of aminotransferases and concentration of free amino acids in the plasma of rats. 119 42

The distribution of amino acids between plasma, liver and brain was studied in adult male rats, fed a diet containing 8.7, 17 (control animals), 32 and 51% of protein during 15 days. The caloric intake was nearly equal in all groups. The highest food intake was observed in the animals on the low protein diet. Changes in plasma amino acids were variable. In contrast to the behavior of most amino acids in plasma, the branched chain amino acids were highest in the animals fed the 51% protein diet. Despite the low protein intake in the animals fed a 8.7% protein diet, the concentration of serine, glutamic acid, glutamine, glycine, alanine, methionine, isoleucine, leucine, phenylalanine and ornithine were significantly higher compared to control animals, whereas in those receiving a high protein diet, valine, leucine, tyrosine, tryptophan and histidine increased in relation to the increased protein and amino acid intake. The plasma amino acid patterns are not greatly influenced by the amino acid distribution in the food and the amount ingested. Alanine aminotransferase, aspartate aminotransferase, glutamate dehydrogenase and cholinesterase showed a two- to fivefold increased activity in the liver of animals consuming a high protein diet. In the brain, the concentration of valine, leucine, isoleucine, phenylalanine and tyrosine in animals receiving the low protein diet was higher than in controls and increased further with increasing protein content of the diet. Glutamine was increased in all dietary groups. The predicted influx of amino acids showed increasing influx rates in dependence of the plasma amino acid concentration. The entry of tyrosine and tryptophan and their brain concentration was inversely proportional to the protein content of the diet. In the present study which considers long-term adaptation to an increasing protein and amino acid intake in comparison to a balanced control protein diet, the levels of the indispensable amino acids were maintained within narrow limits in the brain and liver. The results indicate that inspite of a variable protein intake, the body tends to keep organ amino acids in relatively narrow limits favoring in this way amino acid homeostasis.
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PMID:Effect of different protein diets on the distribution of amino acids in plasma, liver and brain in the rat. 159 Jun 69


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