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)

The aromatic amino acid aminotransferase was purified to a homogenous state from a gramicidin S-producing strain of Bacillus brevis. The enzyme shows a molecular weight of about 71,000 on gel-filtration. The subunit molecular weight is about 35,000 as determined by sodium dodecyl sulfate gel electrophoresis, indicating that the enzyme is a dimer. The enzyme exhibits absorption maxima near 425 and 330 nm at neutral pH. One mole of pyridoxal phosphate is bound per subunit. The enzyme has amino donor specificity for aromatic amino acids, L-phenylalanine, L-tyrosine, and L-tryptophan, and utilizes 2-oxoglutarate as the amino acceptor. This enzyme activity was separated from both the aspartate aminotransferase activity and the branched chain amino acid aminotransferase activity by chromatography on DEAE-Sephadex.
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PMID:Purification and properties of the aromatic amino acid aminotransferase from gramicidin S-producing Bacillus brevis. 244 Aug 56

The autonomic mechanisms of fasting-induced bradycardia of cattle were studied using heart rate spectral analysis. This was performed on digitized, lead II, surface electrocardiograms from conscious, fed, and 48-h-fasted adult cows. Fasting resulted in a significant (P less than 0.05) decrease in resting heart rate and a significant (P = 0.0041) increase in low frequency (0-90 mHz) power spectral area. Administration of atropine sulfate (0.02 mg/kg iv) in either the fed or fasted state resulted in a significant (P less than 0.001) decrease in both low-frequency and high-frequency (100-400 mHz) power spectral areas. Significant (P less than 0.05) increases in serum total bilirubin, inorganic phosphorus, and total protein were associated with fasting. Significant decreases were seen in fasting serum aspartate aminotransferase and potassium values. Manual evacuation of the rumen of seven steers with chronic rumen fistulae resulted in a mean percent decrease in heart rate of 22 +/- 0.9% (mean +/- SE). These results indicate that in normal cattle a decrease in ruminorecticular fill results in a reflex slowing of the heart rate, due predominantly to an increase in parasympathetic tone.
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PMID:Heart rate spectral analysis of fasting-induced bradycardia of cattle. 260 92

The precursor to rat liver mitochondrial aspartate aminotransferase has been expressed in Escherichia coli JM105 using the pKK233-2 expression vector. This mammalian natural precursor has been isolated as a soluble dimeric protein. The amino-terminal sequence and the amino acid composition of the isolated protein correspond to those predicted from the inserted cDNA (Mattingly, J. R., Jr., Rodriguez-Berrocal, F. J., Gordon, J., Iriarte, A., and Martinez-Carrion, M. (1987) Biochem. Biophys. Res. Commun. 149, 859-865). The isolated precursor contains bound pyridoxal phosphate and shows catalytic activity with a specific activity equal to that of the mature form of the enzyme. This precursor can also be processed by mitochondria into a form with the sodium dodecyl sulfate-polyacrylamide gel electrophoresis mobility of mature enzyme. The isolation of this precursor as a stable and catalytically active entity indicates that the presequence peptide does not necessarily interfere with much of the folding and basic structural properties of the mature protein component.
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PMID:Isolation and properties of a liver mitochondrial precursor protein to aspartate aminotransferase expressed in Escherichia coli. 264 43

Experiments were undertaken to examine the ability of selenium to protect against acetaminophen-induced hepatotoxicity and to examine possible mechanisms for this protective effect. Pretreatment of male, Sprague-Dawley rats with sodium selenite (12.5 mumol Se/kg, ip) 24 hr prior to acetaminophen administration produced a significant protection against the hepatotoxic effects of acetaminophen as assessed by a decrease in the plasma appearance of alanine aminotransferase and aspartate aminotransferase activities following acetaminophen. This was accompanied by an increase in the hepatic glutathione levels in selenium-treated animals and an inhibition in the decrease in hepatic glutathione content observed in animals receiving hepatotoxic doses of acetaminophen. Selenium pretreatment decreased the in vivo covalent binding of acetaminophen metabolites to hepatic protein, but did not alter hepatic microsomal cytochrome P-450 content or NADPH cytochrome c reductase activity, suggesting that selenium does not significantly alter the metabolism of acetaminophen to reactive electrophilic metabolites by the cytochrome P-450-dependent mixed-function oxidase enzyme system. Selenium produced an increase in the activity of gamma-glutamylcysteine synthetase which may account for the increased glutathione availability in selenium-treated animals and increased the activities of glutathione S-transferase and glucose-6-phosphate dehydrogenase. Examination of the urinary metabolite profile in selenium-treated animals revealed that the urinary excretion of acetaminophen and its metabolites was significantly increased over a 72-hr period. The increase occurred in the AAP-glucuronide metabolite while parent AAP and AAP-sulfate were actually decreased in selenium-treated rats. No change in recovery was observed in the AAP-glutathione or AAP-mercapturate urinary metabolites. While the glutathione conjugating system is enhanced by selenium treatment, amelioration of acetaminophen toxicity is most likely the result of enhanced glucuronidation which effectively diverts the amount of acetaminophen to be converted by the cytochrome P-450 system to the toxic metabolite.
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PMID:Protective effects of selenium on acetaminophen-induced hepatotoxicity in the rat. 290 Nov 47

Extracts of the leaf tissue of Panicum maximum Jacq. var. trichoglume Eyles (a phosphoenolpyruvate carboxykinase type of C4 plant) were examined and at least two isoforms of aspartate aminotransferase (EC 2.6.1.1), with different electrophoretic mobilities, were detected. The predominant isoform was purified to homogeneity from mesophyll cells. The purification procedure included fractionation with ammonium sulfate followed by chromatography on diethylaminoethyl-cellulose, Sephacryl S-300, and hydroxyapatite. The purified enzyme had specific activities of 182 and 165 mumol/min/mg protein, measured in terms of the synthesis of oxaloacetate and aspartate, respectively, at pH 8.0. The enzyme, with an apparent molecular size of 100 kDa, appears to be a dimer of a single polypeptide with a molecular size of 42 kDa. Mono specific polyclonal antibodies were raised against the 42-kDa polypeptide. Only a single stained band was detected in extracts of whole leaves by immunoblot analysis with this antibody after two-dimensional polyacrylamide electrophoresis. Furthermore, no difference in mobility was observed between the enzymes extracted from mesophyll and bundle sheath cells on native polyacrylamide gels. These findings are discussed in relation to the other isoform in the leaves of this species.
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PMID:Aspartate aminotransferase from Panicum maximum Jacq. var. trichoglume Eyles, a C4 plant: purification, molecular properties, and preparation of antibody. 293 Jan 93

Cytosolic and mitochondrial isoenzymes of aspartate aminotransferase (EC 2.6.1.1) were purified to homogeneity from chicken liver, without previous fractionation of the subcellular components. The procedure includes initial heat treatment and ammonium sulfate fractionation. The two isoenzymes can then be separated by a DEAE-Sepharose chromatography using a linear gradient of L-aspartate (reaction substrate). The separated fractions can be further purified by a parallel step with HA-Ultrogel prior to octyl-Sepharose (c-AAT) and CM-Sepharose (m-AAT) chromatographies. Michaelis constants, pI values, inhibition by adipate and subforms generation with time were studied for both isoenzymes.
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PMID:Simultaneous purification and characterization of aspartate aminotransferase isoenzymes from chicken liver. 323 18

Cysteinesulfinate decarboxylase, purified from male rat livers and homogeneous by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, is resolved into five distinct enzyme species (isoforms) by gel isoelectric focusing. Since the isoforms are present in fresh liver homogenates and do not arise by proteolysis, the enzyme is apparently heterogeneous in vivo. Although female rat livers contain only 5% of the cysteinesulfinate decarboxylase activity of male livers, immunological and enzymatic studies indicate that the distribution of isoforms is similar in both sexes. Rat brain and kidney also contain multiple isoforms which are cross-reactive with polyclonal antibodies prepared to the liver enzyme. The enzyme exhibits a protomer Mr of 53,000, and the native enzyme is shown by cross-linking studies to be dimeric. Purified enzyme contains no carbohydrate or phosphate and does not bind excess pyridoxal 5'-phosphate. Two pools of enzyme activity are resolved preparatively by chromatofocusing chromatography and have been examined with respect to substrate and inhibitor specificity. Both pools are most active toward L-cysteinesulfinate and L-cysteinesulfonate. Aspartate, homocysteinesulfinate, homocysteinesulfonate, 2-amino-3-phosphonopropionate, and glutamate are decarboxylated at rates less than 1% of that observed with L-cysteinesulfinate; D-cysteinesulfinate is not decarboxylated but is an effective inhibitor. The enzyme isoforms cannot be distinguished on the basis of substrate affinity or specificity. The enzyme is irreversibly inactivated by the mechanism-based inhibitors beta-methylene-DL-aspartate and beta-ethylidene-DL-aspartate. beta-Ethylideneaspartate, in contrast to the beta-methylene derivative, does not inhibit aspartate aminotransferase, an enzyme also important in cysteinesulfinate metabolism. beta-Ethylidene aspartate or related beta-ethylidene compounds may be useful in selectively altering cysteinesulfinate metabolism in vivo.
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PMID:Multiple forms of rat liver cysteinesulfinate decarboxylase. 358 15

Mitochondrial aspartate aminotransferase is synthesized on free polysomes as a higher molecular weight precursor (Sonderegger, P., Jaussi, R., Christen, P., and Gehring, H. (1982) J. Biol. Chem. 257, 3339-3345). The present study examines whether the coenzyme pyridoxal phosphate or pyridoxamine phosphate is required for the uptake of the precursor into mitochondria. Chicken embryo fibroblasts were cultured in medium prepared with and without pyridoxal. In cells grown in the presence of pyridoxal only holoform of aspartate aminotransferase and no apoenzyme was detected. Cells cultured under pyridoxal deficiency contained about 30% of apoenzyme in secondary cultures. All of this apoform was identified as mitochondrial isoenzyme. In order to differentiate whether this apoenzyme corresponded to newly synthesized protein or originated from pre-existing holoenzyme, double isotope-labeling experiments were performed. Secondary cultures of chicken embryo fibroblasts grown under pyridoxal depletion were labeled with [3H]methionine, and then pulsed with [35S]methionine. In another series of experiments, the 3H-labeled cells were pulsed with [35S]methionine in the presence of the protonophore carbonyl cyanide m-chlorophenylhydrazone in order to accumulate the precursor. Subsequently, the accumulated precursor was chased into the mitochondria by addition of the carbonyl cyanide m-chlorophenylhydrazone antagonist cysteamine. The holo- and apoenzyme from the ultrasonic extract of the double-labeled cells were separated by affinity chromatography on a phosphopyridoxyl-AH-Sepharose column, immunoprecipitated, and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography. Under both experimental conditions, the 3H/35S ratio of the apoenzyme was less than half of that of the holoenzyme. Therefore, the apoenzyme and not the holoenzyme is the first product of the precursor in the mitochondria. Apparently, the precursor of mitochondrial aspartate aminotransferase is transported into mitochondria as apoprotein and is processed there independently of the coenzyme.
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PMID:The precursor of mitochondrial aspartate aminotransferase is translocated into mitochondria as apoprotein. 373 49

The role of glucocorticoids in the increase by cold-exposure of the effect of alanine on the malate-aspartate shuttle was studied in perfused rat liver. The capacity of the shuttle was evaluated by measurement of changes in both the rate of glucose production from sorbitol and the ratio of lactate to pyruvate during ethanol oxidation (Biomed. Res. 6, Suppl., 1986). The effect of alanine on the shuttle capacity was decreased by adrenalectomy. When 1.5 mg/kg dexamethasone sulfate was administrated to adrenalectomized rats kept at 24 or 4 degrees C, once daily for 5 days, the effect of alanine on the shuttle increased its capacity to the level of sham-operated rats that had been exposed to 4 degrees C for 5 days. The effects of dexamethasone were blocked by the coadministration of tetracycline with the agent. Cold exposure and steroid replacement had little effect on the alanine-induced elevation of the levels of aspartate, glutamate, and alpha-ketoglutarate in liver cells. The increase of the effect of alanine could not be explained only by changes in the activity of NAD+ malate dehydrogenase and aspartate aminotransferase. The results suggest that cold exposure and replacement treatment with glucocorticoids modulate equally the effect of alanine on the capacity of the malate-aspartate shuttle.
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PMID:Effects of alanine on malate-aspartate shuttle in perfused livers from cold-exposed rats. 376 24

The effect of sodium salicylate (SS) pretreatment on acetaminophen (APAP) metabolism and hepatotoxicity in mice was studied. Mice were given a single oral dose of SS (100 mg/kg) 1 hr before graded doses of APAP (150-500 mg/kg). Liver histology, serum hepatic enzymes (serum glutamic-oxaloacetic transaminase, serum glutamic-pyruvic transaminase and isocitric dehydrogenase) and APAP metabolites in urine were examined 24 hr after APAP treatment. Free plasma APAP and liver glutathione were determined over 24 hr after treatment with 400 mg/kg of APAP alone or after SS pretreatment. At 500 mg of APAP per kg, mortality rate was 38% in SS + APAP group; no mortality was seen among animals treated with APAP alone. Centrilobular hepatic hemorrhagic necrosis and/or vacuolation were observed in both treatments. Mitosis of hepatocytes was increased in all APAP-treated mice. Incidence of hepatic necrosis and mean lesion grades at 300- and 500-mg/kg doses increased in mice pretreated with SS. Mice that received SS + APAP had significantly higher levels of serum glutamic-oxaloacetic transaminase, serum glutamic-pyruvic transaminase and isocitric dehydrogenase at all doses compared to mice treated with APAP alone. APAP glucuronide and sulfate conjugates decreased and APAP mercapturate conjugate increased in urine of mice receiving SS + APAP treatment. Free plasma APAP was significantly higher 2 hr after APAP treatment in SS + APAP-treated mice as compared to mice that received APAP alone. Hepatic glutathione levels were similarly decreased over 24 hr in both groups. These data demonstrate that SS pretreatment alters APAP biotransformation profile and potentiates the hepatotoxic effect of APAP in mice.
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PMID:Potentiation of the hepatotoxic effect of acetaminophen by prior administration of salicylate. 398 58


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