Figure. Androgen biosynthesis pathways.
The basic pathways are demarcated with respect to CYP17A1 and SRD5A activities. The 17-deoxy, 21-carbon steroids upstream of CYP17A1 are shown at left in green box, including 11-deoxycorticosterone (DOC). The 17-hydroxy, 21-carbon steroids are in center in peach box, and 19-carbon steroids are at right in blue box, generated via 17-hydroxylase and 17,20-lyase reactions of CYP17A1, respectively. The 5-reduced steroids are highlighted with darker background at lower right. Reversible interconversions catalyzed by HSDs are shown with double arrows at terminal steps. CYP17A1, cytochrome P450c17; 3β-HSD, 3-beta-hydroxysteroid dehydrogenase/isomerase; 11 α -HSD, 11-beta-hydroxysteroid dehydrogenase; 17β-HSD, 17-beta-hydroxysteroid dehydrogenase; 3α-HSD, 3-alpha-hydroxysteroid dehydrogenase; SRD5A, steroid 5α reductase; DHEA, Dehydroepiandrosterone; DHEA-S, Dehydroepiandrosterone sulfate; STS, steroid sulfatase; SULT2A1, sulfotransferase 2A1