**4.3 17 -Hydroxylase/17,2O-Desmolase**

The 17 -Hydroxylase/17,2O-Desmolase (P-45Oc7f or CYP17A1 lTl) is a cytochrome P450 enzyme with 17-hydroxylase and 17,20-lyase activities that catalyzes two reactions: the hydroxylation of pregnenolone and progesterone at carbon 17, and the conversion of pregnenolone into C-19 steroids. P-450c17 is a key enzyme in the steroidogenic pathway producing all steroid hormones (progestins, mineralocorticoids, glucocorticoids, androgens, and estrogens). The theca cells of the follicle and the theca lutein cells of the corpus luteum, as well as the ovarian stroma, the adrenal gland, and Leydig cells express P-450c17. (Auchus & Miller, 2000; Straus & Hsue, 2000).
