Bifunctional enzyme that catalyzes the oxidation of the 3-beta-hydroxy group of cholesterol and the isomerization of the double bond of the resulting product, producing cholest-4-en-3-one. These reactions are part of a cholesterol degradation pathway that allows the bacterium to utilize cholesterol as its sole source of carbon and energy. cholesterol + O2 = cholest-5-en-3-one + H2O2 cholest-5-en-3-one = cholest-4-en-3-one kcat is 44 sec(-1) for the oxidation of cholesterol. kcat is 64 sec(-1) for the isomerization of cholest-5-en-3-one. Steroid metabolism; cholesterol degradation. Monomer. Predicted to be exported by the Tat system. The position of the signal peptide cleavage has been experimentally proven. Belongs to the GMC oxidoreductase family.