Requires NADPH and EC 1.6.2.4, NADPH---hemoprotein reductase. A microsomal hemeprotein that catalyses two independent reactions at the same active site - the 17alpha-hydroxylation of pregnenolone and progesterone, which is part of glucocorticoid hormones biosynthesis, and the conversion of the 17alpha-hydroxylated products via a 17,20-lyase reaction to form androstenedione and dehydroepiandrosterone, leading to sex hormone biosynthesis (EC 1.14.14.32, 17alpha-hydroxyprogesterone deacetylase). The ratio of the 17alpha-hydroxylase and 17,20-lyase activities is an important factor in determining the directions of steroid hormone biosynthesis towards biosynthesis of glucocorticoid or sex hormones.
Requires NADPH and EC 1.6.2.4, NADPH---hemoprotein reductase. A microsomal hemeprotein that catalyses two independent reactions at the same active site - the 17alpha-hydroxylation of pregnenolone and progesterone, which is part of glucocorticoid hormones biosynthesis, and the conversion of the 17alpha-hydroxylated products via a 17,20-lyase reaction to form androstenedione and dehydroepiandrosterone, leading to sex hormone biosynthesis (EC 1.14.14.32, 17alpha-hydroxyprogesterone deacetylase). The ratio of the 17alpha-hydroxylase and 17,20-lyase activities is an important factor in determining the directions of steroid hormone biosynthesis towards biosynthesis of glucocorticoid or sex hormones.
GenBank accession numbers L40335 and AF251388 encodíng isozymes 1 and 2; two isozymes of cytochrome P450 17alpha-hydroxylase/17,20-lyase, that differ in two nucleotides, resulting in variants Ser210Gly and Tyr464Asn
the CYP17 enzymes from various species have 46-98% sequence homology, depending on the evolutionary distance between the organisms. Enzymes from different mammalian species show relatively high homology of amino acid sequences, but have different types of activity and different requirements for cytochrome b5
the following factors contribute to the regulation of CYP17 activities: 1. the ratio of NADPH-cytochrome P450 reductase to CYP17, i.e. the rate of delivery of reducing equivalents to the P450, 2. the presence of cytochrome b5 either as an allosteric effector or as an electron donor, 3. phosphorylation of the CYP17 protein, which affects its stability and activity, and 4. retention of the intermediate, 17-OHP5 or 17-OHP4, in the active site of CYP17, which facilitates the 17,20-lyase reaction. Expression level of CYP17A1 in adrenals is regulated by ACTH and by gonadotropic hormone in the testis and ovaries