Aromatase and nonaromatizing 10-demethylase activity of adrenal cortex mitochondrial P-450(11)beta

19-Oxoandrostenedione, the product of 19-hydroxyandrostenedione by the 19-oxidase activity of the purified P-450(11)beta system of adrenal cortex mitochondria, was further oxidized and demethylated at the 10-position to give the C18-steroids, estrone (aromatase reaction) and 19-norandrostenedione (nonaromatizing 10-demethylase or C10-19 lyase reaction). These reactions, together with the initial hydroxylation of androstenedione at C19, form a sequence of P-450(11)beta-catalyzed C19-steroid 19-monooxygenase reactions. P-450(11)beta is thus similar to placental endoplasmic P-450AROM in some of its substrate specificity, but the two forms of P-450 appear to be different in both physiology and properties.