Significance of cytochrome P-450 (P-450 HFLa) of human fetal livers in the steroid and drug oxidations.

The purpose of this study was to clarify the pharmacological and physiological significance of P-450 HFLa. Thus, correlations between cytochrome P-450 (P-450 HFLa) level and different monooxygenase activities were investigated in liver homogenates from human fetuses. Poor correlation was seen between P-450 HFLa level and the activity of benzphetamine N-demethylation or aniline hydroxylation. In contrast, the content of P-450 HFLa was highly correlated with the activity of benzo(a)pyrene hydroxylation, 7-ethoxycoumarin O-deethylation or testosterone 6 beta-hydroxylation. In microsomes from human adult livers, a moderate relationship was also observed between testosterone 6 beta-hydroxylation and P-450 HFLa level. Furthermore, antibodies to P-450 HFLa inhibited testosterone 6 beta-hydroxylase activity in fetal and adult livers to similar extents. We conclude that P-450 HFLa is a form of cytochrome P-450 which catalyzes testosterone 6 beta-hydroxylation and limited drug oxidations in human fetal and adult livers.