-!- Requires NADPH and EC 1.6.2.4. -!- Catalyzes two independent reactions at the same active site - the 17-alpha-hydroxylation of pregnenolone and progesterone, which is part of glucocorticoid hormones biosynthesis, and the conversion of the 17-alpha-hydroxylated products via a 17,20-lyase reaction to form androstenedione and dehydroepiandrosterone, leading to sex hormone biosynthesis (EC 1.14.14.32). -!- The ratio of the 17-alpha-hydroxylase and 17,20-lyase activities is an important factor in determining the directions of steroid hormone biosynthesis toward biosynthesis of glucocorticoid or sex hormones. -!- Formerly EC 1.14.1.7, EC 1.14.99.9 and EC 1.99.1.9.

-!- A microsomal protein that catalyzes two independent reactions at the same active site - the 17-hydroxylation of pregnenolone and progesterone, which is part of glucocorticoid hormones biosynthesis (EC 1.14.14.19), and the conversion of the 17-hydroxylated products via a 17,20-lyase reaction to form androstenedione and 3-beta- hydroxyandrost-5-en-17-one, leading to sex hormone biosynthesis. -!- The activity of this reaction is dependent on the allosteric interaction of the enzyme with cytochrome b5 without any transfer of electrons from the cytochrome. -!- The enzymes from different organisms differ in their substrate specificity; while the enzymes from pig, hamster, and rat accept both 17-alpha-hydroxyprogesterone and 17-alpha-hydroxypregnenolone, the enzymes from human, bovine, sheep, goat, and bison do not accept the former, and the enzyme from guinea pig does not accept the latter. -!- Formerly EC 4.1.2.30.