Cytochrome P-450scc-catalyzed production of progesterone from cholestenone.

Cholestenone, which is a 3-keto derivative of cholesterol, was incubated with cytochrome P-450SCC in a reconstituted hydroxylation system. Cholestenone was metabolized to progesterone with a turnover number of about 9 nmol/min/nmol P-450 in the presence of 0.01% Tween20. This value was about 70% of the maximal value for cholesterol. The final reaction product, progesterone, and three other minor reaction products, 20 alpha-hydroxycholest-4-en-3-one, 22R-hydroxycholest-4-en-3-one, 20,22-dihydroxycholest-4-en-3-one, were identified on the basis of its retention times on HPLC, thus suggesting them to be intermediates of side-chain cleavage of cholestenone. The results suggest that cholestenone is metabolized by two pathways, that is, the first hydroxylation occurs either at the C-20 position or at the C-22 position.