Biological aromatization of steroids.

The conversion of androgenic steroids to the phenolic estrogens by mammalian tissue has been well documented. The reaction has been reported in relatively low yield, in vitro with ovarian and placental slices (l-3), and in viva after the administration of androgens to various species including man (4, 5). The present report describes the conversion of androgens to estrogens in high yield by a system consisting of human placental microsomes, the reduced form of triphosphopyridine nucleotide, and oxygen. Localization of the enzymatic activity has permitted evaluation of enzyme kinetics, cofactor requirements, and substrate specificity. A preliminary note on the conversion of A4-androstene-3, 17-dione to estrone by this system has been published (6).