OXIDATION OF CHOLESTEROL AND CHOLESTEROL ANALOGS BY MITOCHONDRIAL PREPARATIONS OF STEROID-HORMONE-PRODUCING TISSUE

The rate of oxidation of cholesterol and its analogs to pregnenolone(3.beta.-hydroxypregn-5-en-20-one) by various mitochondrial preparations [pig testis, rat adrenal, bovine adrenal cortex] was measured. Sterols with the cholest-5-en-3.beta.-ol ring system and saturated side chains of different lengths were converted into pregnenolone at rates similar to that of cholesterol. This marked lack of mitochondrial specificity towards the steroid side chain is in direct contrast with the rat liver microsomal cholesterol 7.alpha.-hydroxylase, which has a high specificity for the side chain. Steroids that retain the ring system, but contain hydroxyl groups at various points in the side chain, are converted into pregnenolone at rates 3 to 8 times higher than is cholesterol. The results are discussed with reference to current ideas on the mechanism of the side-chain cleavage of cholesterol.