Transformation of labeled cholesterol, 20α-hydroxycholesterol, (22R)-22-hydroxycholesterol, and (22R)-20α, 22-dihydroxycholesterol by adrenal acetone-dried preparations from Guinea pigs, cattle and man: II. Kinetic studies

Oxysterols: Modulators of Cholesterol Metabolism and Other Processes

“…It is well established that (22R)-22-OH-Chol and (20R,22R)-20,22-diOH-Chol can be converted to pregnenolone in steroid hormone-forming organs and that the enzyme catalyzing these conversions and their formation from Chol, Chol-side-chain cleavage enzyme (P-450 scc ), is localized in mitochondria (7, 148 and references cited therein). (20S)-20-OH-Chol can also act as a substrate for pregnenolone formation (7,146,147,149,541) but is not considered to be an intermediate in the overall conversion of Chol to pregnenolone (148,1063,1135). Ketoconazole has been reported (1088) to inhibit progesterone formation from labeled Chol in JEG-3 choriocarcinoma cells, an effect that was ascribed to an inhibition of the P-450 scc .…”

Cholesterol Metabolism and Steroid-Hormone Production

“…Chaudhuri et al (1962) showed that (22R)-22-hydroxycholesterol was converted into pregnenolone. Burstein et al (1970), by a kinetic approach using radioactive sterols and an acetone-dried-powder preparation of bovine adrenal mitochondria concluded that the formation of (20S)-20-hydroxycholesterol from cholesterol is a slower reaction than that involving the production of (22R)-22-hydroxychoIesterol; they also concluded that the rate of (22R)-22-hydroxycholesterol utilization for pregnenolone synthesis was greater than the rate of utilization of (20S)-20-hydroxycholesterol. Van Lier & Smith (1970) have shown that c~olesterol-(20S)-20-hydroperoxide is converted into (20R,22R)-20,22-dihydroxycholesterol by a rearrangement of this peroxide.…”

Incorporation of H218O into 20α, 22R‐di‐OH cholesterol: Evidence for an epoxide—diol pathway in the adrenocortical cholesterol side‐chain cleavage mechanism

“…The calculations made by Bustein et al [6] led them to the conclusion that the pathways via the mono-hydroxylated sterols contributed only a small part to pregnenolone formation from cholesterol and that the most important pathway consisted of a direct conversion of cholesterol into 2Oq22R. Very recently [ 131 these authors however have drastically altered the interpretation of their experiments.…”