Eigenschaften von aromatischen Aminosäure-Aminotransferasen aus zwei Chloramphenicol-resistenten Flavobakterien

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Abstract
Two enzymes of chloramphenicol-resistant Flavobacterium strain CB 60 and strain CB 6 which catalyze the transamination of tyrosine, phenylalanine and tryptophan were enriched 43-fold and 31-fold. The MW for the aromatic-amino-acid aminotransferases of both strains was 120,000 daltons and the isoelectric point was .apprx. pH 4.2-4.3. Both enzymes are not influenced by EDTA. A ping pong bi-bi-mechanism was obtained for the kinetic mechanism of the reaction. The aminotransferases of strain CB 60 and CB 6 differ in the pH optimum (pH 8.4-9.0 and 7.8-9.0), in the optimum of temperature (40.0.degree. and 57.5.degree. C) and in a higher heat stability of the enzyme of strain CB 60 in comparison to that of strain CB 6. The catalytic activity of the enzyme of strain CB 60 is not influenced by cycloserine, contrary to the enzyme of CB 6 which is inhibited to 89%. Isonicotinohydrazide does not inhibit the enzyme of strain CB 6, but reduces the catalytic activity of the enzyme of strain CB 60 to 64%. Both enzymes are inhibited differently by phenylhydrazine [78% (CB 60) and 56% (CB 6)]. Data in percentages are related to 0.15 mM inhibitor. For the substrates tyrosine, phenylalanine, tryptophan and 2-oxoglutarate, the aminotransferase of strain CB 60 has Km values of 15.0, 16.6, 16.6 and 1.7 mM, and for the enzyme of strain CB 6, Km values of 1.40, 1.33, 1.37 and 0.97 mM were obtained.