EFFECT OF NONIONIC DETERGENTS ON APPARENT ENZYME MECHANISM - V121A MUTANT OF STREPTOMYCES CHOLESTEROL OXIDASE ENDOWED WITH ENHANCED SENSITIVITY TOWARDS DETERGENTS

One of the mutants of Streptomyces cholesterol oxidase with the Val121 Ala mutation (V121A) was kinetically analysed. Although the reaction r ate-substrate concentration curve of wild type follows a simple Michae lis-Menten equation, that of V121A is sigmoidal. The cooperativity was apparent and caused by non-ionic detergents that were used as a solve nt of cholesterol. The concentration dependence of V121A on detergents was more significant than that of wild type, although the reaction ra tes of both enzymes decrease as the concentrations of detergents incre ase. Further experiments suggested that less hydrophobic interactions between V121A and detergents should be responsible for the apparent co operativity. Since Val121 is in a hydrophobic loop located near the ac tive site, the mutational effect is structurally discussed.