A sex-specific form of cytochrome P-450 catalyzing propoxycoumarin O-depropylation and its identity with testosterone 6β-hydroxylase in untreated rat livers: Reconstitution of the activity with microsomal lipids

Characteristics of a typical male-dominant reaction, dealkylation of n-propoxycoumarin, in rat livers were studied in relation to microsomal testosterone 6β-hydroxylase. The depropylation was more than 10-fold higher in the liver of male than female adult rats, but the sex-related difference was eliminated by neonatal castration. Hypophysectomy of adult male rats, which decreased the rates of male-specific P-450-male-dependent reactions, increased the depropylation of propoxycoumarin, while the rate was decreased by either intermittent injection or continuous infusion of human growth hormone to hypophysectomized rats. With regard to age-related difference, microsomal depropylation was detectable at neonate and reached a maximal level at 14 to 20d of age, but was abruptly diminished only in female rats at puberty. These changes are in good agreement with those of testosterone 6β-hydroxylation and the content of a male-specific P-450_6β-1/PB-1. In reconstituted systems using extracted microsomal lipids, P-450_6β-1/PB-1 and P-450-male catalyzed the depropylation of propoxycoumarin. However, the microsomal depropylation was inhibited by antibodies which recognize P-450_6β-1/PB-1 but not P-450-male. These results indicate that microsomal depropylation of propoxycoumarin is catalyzed mainly by a male-specific P-450_6β-1/PB-1 in livers of untreated rats.