Tyrosine aminotransferase in AKR/J albino and C57BL/6J black mouse skin
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L-Tyrosine aminotransferase is present in a high speed supernatant fraction of skin homogenate of AKR/J albino and C57BL/6J black mice. The conversion of tyrosine to p-hydroxyphenylpyruvate was shown to be catalyzed by an aminotransferase by the following observations: the reaction was partially dependent on the presence of low concentrations of alpha-ketoglutarate; catalase was ineffective in increasing the yield of p-hydroxyphenylpyruvate; there was potent inhibition by typical inhibitors of pyridoxal phosphate enzymes and of rat liver tyrosine aminotransferase; there was no inhibition by inhibitors of L-amino acid oxidase; and there was no oxidation of L-leucine, the best substrate for rat kidney L-amino acid oxidase. The aminotransferase was stimulated by mercaptoethanol and was inhibited by high concentrations of alpha-ketoglutarate. The apparent Km for tyrosine was 5 X 10(-3) M and the molecular weight, determined by sucrose density gradient centrifugation, was 150-200,000. Dopa was also transaminated by the crude enzyme. No tyrosine aminotransferase could be detected in extracts of hamster melanoma.
L-Tyrosine aminotransferase is present in a high speed supernatant fraction of skin homogenate of AKR/J albino and C57BL/6J black mice. The conversion of tyrosine to p-hydroxyphenylpyruvate was shown to be catalyzed by an aminotransferase by the following observations: the reaction was partially dependent on the presence of low concentrations of alpha-ketoglutarate; catalase was ineffective in increasing the yield of p-hydroxyphenylpyruvate; there was potent inhibition by typical inhibitors of pyridoxal phosphate enzymes and of rat liver tyrosine aminotransferase; there was no inhibition by inhibitors of L-amino acid oxidase; and there was no oxidation of L-leucine, the best substrate for rat kidney L-amino acid oxidase. The aminotransferase was stimulated by mercaptoethanol and was inhibited by high concentrations of alpha-ketoglutarate. The apparent Km for tyrosine was 5 X 10(-3) M and the molecular weight, determined by sucrose density gradient centrifugation, was 150-200,000. Dopa was also transaminated by the crude enzyme. No tyrosine aminotransferase could be detected in extracts of hamster melanoma.