[Change of cholesterol oxidase of Brevibacterium sterolicum and substrate specificity].

Cholesterol oxidase modified by hydrogen peroxide is inactive with cholesterol solubilized in buffer with surfactants. Pregn-5-en-3 beta-ol when solubilized in the same conditions and substrates soluble in buffer, like 3 beta-hydroxy-androst-5-en-17-one or 3 beta-hydroxy-androst-5-en-17 beta-carboxylic acid are substrates of the modified enzyme. The observed loss of activity on cholesterol could be due to the inability of the oxidized cholesterol oxidase to extract cholesterol from mixed cholesterol/surfactant aggregates. Cholesterol oxidase on storage undergoes modifications close to those with hydrogen peroxide and care should be taken for the use of cholesterol oxidase as cholesterol probe.