Inhibition of cholesterol side-chain cleavage by 22-azacholesterol

Abstract

The side-chain of cholesterol is oxidatively cleaved by a cytochrome P-450-dependent enzyme system present in mammalian adrenal mitochondria. The reaction was postulated to proceed via one or more hydroxylated intermediates. Inhibition of the reaction by the potent inhibitor 22-azacholesterol did not result in a build-up of the postulated intermediates: (20S)-20-hydroxycholesterol, (22R)-22-hydroxycholesterol, (20R,22R)-20,22-dihydroxycholesterol or (20S)-cholesterol hydroperoxide. Spectral studies indicate a modified type II spectrum for the reaction of 22-azacholesterol with adrenal mitochondrial cytochrome P-450. In addition, spectral and electron spin resonance studies indicate a common interaction of cholesterol and 22-azacholesterol with the cytochrome. Although this study does not resolve the question of the intermediacy of the oxygenated derivatives in the cleavage reaction, it indicates that the binding of 22-azacholesterol depends on its steroid structure rather than on its amine character. A discussion of the proximity of the heme to the substrate binding site is also presented.