 P450scc catalyzes the conversion of cholesterol to pregnenolone in three monooxygenase reactions.These involve 2 hydroxylations of the cholesterol side-chain, which generate, first, 22R-hydroxycholesterol and then 20alpha,22R-dihydroxycholesterol.The final step cleaves the bond between carbons 20 and 22, resulting in the production of pregnenolone and isocaproic aldehyde.