Spin state changes in cytochrome P‐450 associated with cholesterol side chain cleavage in bovine adrenal cortex mitochondria

Kinetic studies on substrate-enzyme interaction in the adrenal cholesterol side-chain cleavage system

“…A biphasic formation of corticosterone from endogenous precursors has been described by Koritz and Kumar (1970) in succinate-supplemented rat adrenal mitochondria. A similar time course for pregnenolone formation was also seen by Simpson et al (1971) with bovine adrenocortical mitochondria following the addition of malate. This biphasic behavior was attributed by Koritz and Kumar (1970) to a possible feedback inhibition by pregnenolone, and by Simpson et al (1971) also to a rate-limited transport of cholesterol to the heme protein P-450. Biphasic kinetics have been observed by Sasame and Gillette (1969), by Gigon et al (1969), and by Diehl et al (1970) for the formation of the CO complex of hepatic microsomal heme protein P-450 after the addition of appropriate reducing agents.…”

“…A similar time course for pregnenolone formation was also seen by Simpson et al (1971) with bovine adrenocortical mitochondria following the addition of malate. This biphasic behavior was attributed by Koritz and Kumar (1970) to a possible feedback inhibition by pregnenolone, and by Simpson et al (1971) also to a rate-limited transport of cholesterol to the heme protein P-450. Biphasic kinetics have been observed by Sasame and Gillette (1969), by Gigon et al (1969), and by Diehl et al (1970) for the formation of the CO complex of hepatic microsomal heme protein P-450 after the addition of appropriate reducing agents. Similar biphasic kinetics for the CO complex formation were observed by Ando and Horie (1971) with adrenocortical mitochondrial heme protein P-450.…”