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)

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

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

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

To gain some insight into the role played by certain protein domains in the import of mitochondrial aspartate aminotransferase in isolated mitochondria, three protein mutants were constructed by using the plasmid pOTS-mAspAT, which contains the nucleotide sequence encoding for the mature form of this enzyme. Two mutant proteins in which Cys-166 was substituted with either serine or alanine and another protein lacking the nine N-terminal amino acids were all synthesized in a cell-free transcription/translation system. Comparison was made among the newly synthesized mutant proteins and the newly synthesized wild type aspartate aminotransferase with respect to their capability to enter mitochondria. All the mutant proteins proved to be able to enter mitochondria even though with a lower efficiency than the wild type enzyme. Interestingly the thiol reagent mersalyl proved to inhibit import of both wild type enzyme and serine mutant, whereas import of alanine mutant was found to be insensitive to mersalyl, thus showing that Cys-166 is the unique -SH group involved in import. Import of mitochondrial aspartate aminotransferase by mitochondria is shown to involve certain protein domains present in the mature protein, two of them being the Cys-166 and the N-terminal regions.
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PMID:Import of mutant forms of mitochondrial aspartate aminotransferase into isolated mitochondria. 141 82

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

Stereochemical studies of three pyridoxal phosphate dependent decarboxylases and serine hydroxymethyltransferase have allowed the dispositions of conjugate acids that operate at the C alpha and C-4' positions of intermediate quinoids to be determined. Kinetic work with the decarboxylase group has determined that two different acids are involved, a monoprotic acid and a polyprotic acid. The use of solvent kinetic isotope effects allowed the resolution of chemical steps in the reaction coordinate profile for decarboxylation and abortive transamination and pH-sensitivities gave the molecular pKa of the monoprotic base. Thus the epsilon-ammonium group of the internal aldimine-forming lysine residue operates at C-4'-si-face of the coenzyme and the imidazolium side chain of an active site histidine residue protonates at C alpha from the 4'-si-face. Histidine serves two other functions, as a base in generating nitrogen nucleophiles during both transaldimination processes and as a binding group for the alpha-carboxyl group of substrates. The latter role for histidine was determined by comparison of the sequences for decarboxylase active site tetrapeptides (e.g. -S-X-H-K-) with that for aspartate aminotransferase (e.g. -S-X-A-K-) where it was known, from X-ray studies, that the serine and lysine residues interact with the coenzyme. By using the Dunathan Postulate, the conformation of the external aldimine was modified, and without changing the tetrapeptide conformation, the alanine residue was altered to a histidine. This model for the active site of a pyridoxal dependent decarboxylase was consistent with all available stereochemical and mechanistic data.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:A structural and mechanistic comparison of pyridoxal 5'-phosphate dependent decarboxylase and transaminase enzymes. 167 32

The five cysteines, at positions 82, 191, 192, 270, and 401, of Escherichia coli aspartate aminotransferase (AATase) were, individually and in some combinations, converted to alanine by site-directed mutagenesis (C82A, C191A, C192A, C270A, C401A). Cys-191, which is conserved in all AATase isozymes, was mutated to serine as well (C191S). A quintuple mutant, with all cysteines converted to alanines (Quint), was also constructed. The effects of these single and multiple mutations were examined by steady-state kinetics and urea denaturation. The thermal stabilities of Quint and of the wild-type enzyme (WT) were determined by differential scanning calorimetry. The mutants had kcat values up to 50% greater than that of WT and KMAsp and KM alpha-KG values up to 1.5- and 3.3-fold higher than that of WT. The mutants C82A and C191A exhibit nearly the same CM in urea denaturation experiments as WT, while the other single mutants and Quint are less stable, with CM differences of up to 0.7 M urea. Quint is also less thermostable than WT, with a delta TM of 3.3-4.4 degrees C. Thus the five cysteine replacements yield small, but significant, changes in catalytic and denaturation parameters, but none of the cysteines was found to be essential. The changes manifested in the mutation of the conserved Cys-191 to alanine are no greater than those observed with the four nonconserved cysteines. We consider the evolutionary implications of these findings.
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PMID:Contribution to catalysis and stability of the five cysteines in Escherichia coli aspartate aminotransferase. Preparation and properties of a cysteine-free enzyme. 173 83

Twenty-four hours after acute administration of cocaine HCl (25 mg/kg, i.p.) to male C57BL/6ByJ mice, there was no hepatotoxicity as measured by plasma aspartate aminotransferase (AST) activity. In contrast, daily administration of cocaine (25 mg/kg, i.p.) for 14 days induced marked hepatotoxicity, as characterized by a greater than 400% increase in plasma AST activity when assayed 24 hr after the last injection. Concomitantly, the liver had increased levels of cysteine, gamma-glutamylcysteine, glutathione, cysteinylglycine, glutamate, methionine, taurine, and aspartate. The effect appeared to be selective for compounds of the glutathione metabolic pathways, because repeated cocaine exposure did not affect other amino acids such as leucine, isoleucine, phenylalanine, serine, and valine. There was a positive correlation between the magnitude of the elevation of cysteine and the extent of liver damage. Daily cocaine administration did not affect striatal or frontal cortex glutathione. A final cocaine challenge (50 mg/kg, i.p.) did not affect either hepatic or cerebral glutathione metabolism. The increase in hepatic cysteine and glutathione upon daily cocaine administration is a potentially important compensatory mechanism against cocaine-induced hepatotoxicity.
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PMID:Differential effects of daily administration of cocaine on hepatic and cerebral glutathione in mice. 224 12

Food intake, plasma and brain amino acid concentrations, liver amino acid catabolic enzyme activities, and whole-brain neurotransmitter and metabolite concentrations were measured in young rats adapted for 11 d to diets containing from 5 to 75% (in increments of 5%) casein. Food intake was depressed initially in rats fed diets containing 5, 10% or greater than 35% casein. For the duration of the experiment, food intakes of the groups fed the higher protein diets improved on successive days; the length and severity of the depression were proportional to the protein content of the diet fed. Rats fed low levels of protein grew poorly, and their food intake remained depressed. The gradual improvement in growth and food intake of rats fed diets containing more than 35% casein was accompanied by dramatic increases in the activities of serine-threonine dehydratase (SDH, EC 4.2.1.16) and glutamate-pyruvate aminotransferase (GPT, EC 2.6.1.1) in liver. The increase in amino acid catabolic activity was accompanied by decreases in the concentrations of most amino acids in plasma and brain. However, concentrations of branched-chain amino acids, in both plasma and brain, increased in direct proportion to the protein concentration of the diet fed. As a result of these reciprocal responses, the total concentration of indispensable amino acids in brain (IAA) was maintained within a narrow range of values, despite a sixfold range of protein intakes. Whole-brain concentrations of norepinephrine, dopamine and serotonin were not correlated with dietary protein concentration, total food intake or protein intake. Brain concentrations of homovanillic acid and 5-hydroxyindoleacetic acid were correlated inversely with protein intake and that of 3,4-dihydroxyphenylacetic acid was correlated directly with food intake. Protein intake appeared to be related to the animal's ability to maintain brain total IAA content between some upper and lower limits. Our results indicate that this was accomplished initially through downward adjustment of protein intake and subsequently through an increase in catabolic capacity for the amino acids.
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PMID:Adaptation of rats to diets containing different levels of protein: effects on food intake, plasma and brain amino acid concentrations and brain neurotransmitter metabolism. 285 80

The isolated perfused rat kidney was shown to synthesize serine from aspartate or glutamate, both of which are also precursors of glucose. The major products of aspartate metabolism were ammonia, serine, glutamate, glucose, glutamine and CO2. Perfusion of kidneys with aspartate in the presence of amino-oxyacetate resulted in a near-complete inhibition of aspartate metabolism, illustrating the essential role of aspartate aminotransferase in the metabolism of this substrate. Radioactivity from 14C-labelled aspartate and from 14C-labelled glycerol was incorporated into serine and glucose. Production of both glucose and serine from aspartate was suppressed in the presence of 3-mercaptopicolinic acid. These data provide evidence for the operation of the phosphorylated and/or non-phosphorylated pathway for serine production to the presence of 3-mercaptopicolinic acid. This is explained by simultaneous glycolysis. The rate of glucose production, but not that of serine, was greater in kidneys perfused with glutamate or with aspartate plus glycerol than the rates obtained by perfusion with aspartate alone. These data are taken to suggest that serine synthesis occurred at a near-maximal rate, and that the capacity of the kidney for serine synthesis from glucose precursors is lower than that for glucose synthesis.
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PMID:Serine synthesis by an isolated perfused rat kidney preparation. 286 20


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