Acetylenic mechanism-based inhibitors of cholesterol side chain cleavage by cytochrome P-450scc.

The following acetylenic steroids appear to be the first reported mechanism-based inhibitors of cytochrome P-450scc: 20-(1-propynyl)-5-pregnen-3 beta, 20 alpha-diol, 20-(1-hexynyl)-5-pregnen-3 beta, 20 alpha-diol, and 20-(1,5-hexadiynyl)5-pregnen-3 beta, 20 alpha-diol. Oxygen and NADPH are required for enzymatic oxidation and all three steroids yield pregnenolone as a major product. Incubation of P-450scc with 20-(1,5-hexadiynyl)-5-pregnen-3 beta, 20 alpha-diol under turnover conditions completely inactivates the enzyme with a half-time of 11 min. The partition ratio for inactivation by the steroid was determined to be about 6 molecules of the steroid processed per molecule of P-450scc inactivated.