Requirement of NADPH and molecular oxygen for the side-chain cleavage of 20α, 22ξ-dihydroxycholesterol

Abstract

The NADH-supported cytochrome P-450-dependent 2-hydroxylation of estradiol in rat liver microsomes has been investigated. Estradiol 2-hydroxylation proceeded well with NADH instead of NADPH as a cofactor. Dimethyltetrahydropterine was incapable of serving as a hydrogen donor for this biotrans-formation. When both NADH and NADPH were used, the 2-hydroxylation increased additively. Molecular oxygen dissolved in the incubation medium was enough for the occurrence of the NADH-dependent 2-hydroxylation. The presence of carbon monooxide suppressed the formation of catechol estrogen where the CO/O2 ratio needed for 50% inhibition of the bioconversion was 7.7. The inhibitory effect was reversed completely by illumination with white light. p-Chloromercuribenzoate inhibited almost completely the 2-hydroxylase activity, and the enzyme activity was also inhibited by SK.F-525A. These results strongly imply the possible involvement of a cytochrome P-450 system in the NADH-dependent 2-hydroxylation of estradiol with rat liver microsomes.