title: Expression of bovine 17 alpha-hydroxylase cytochrome P-450 cDNA in nonsteroidogenic (COS 1) cells.
abstract: Cortisol production requires the activity of only 17 alpha-hydroxylase, whereas the formation of sex steroids requires both 17 alpha-hydroxylase and 17,20-lyase activities. Studies in reconstituted enzyme systems have suggested that a single steroid hydroxylase, 17 alpha-hydroxylase cytochrome P-450 (P-450(17) alpha), catalyzes both activities. By expression of bovine adrenocortical P-450(17 alpha) in COS 1 (transformed monkey kidney) cells, which normally contain no detectable P-450(17) alpha, it has now been established in situ that a single polypeptide chain does catalyze both the 17 alpha-hydroxylase and the 17,20-lyase reactions. This heterologous system supports 17 alpha-hydroxylation of pregnenolone and progesterone with equal efficiency, but catalyzes about five times as much 17,20-lyase activity when 17 alpha-hydroxypregnenolone is the substrate than when 17 alpha-hydroxyprogesterone is the substrate. For these activities to be observed in COS 1 cells, newly synthesized apocytochrome P-450(17) alpha must bind heme and insert into the endoplasmic reticulum such that endogenous cytochrome P-450 reductase can support hydroxylation. Thus, COS 1 cells are a useful system for expression and study of various forms of cytochrome P-450.
mesh_terms: D000818:Animals; D002417:Cattle; D002522:Chlorocebus aethiops; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D004247:DNA / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D007668:Kidney / Q000166:cytology; D009097:Multienzyme Complexes / Q000235:genetics / Q000378:metabolism; D011284:Pregnenolone / Q000378:metabolism; D011374:Progesterone / Q000378:metabolism; D013254:Steroid 17-alpha-Hydroxylase / Q000378:metabolism*; D013250:Steroid Hydroxylases / Q000235:genetics / Q000378:metabolism*
chemical_list: D009097:Multienzyme Complexes; D011374:Progesterone; D011284:Pregnenolone; D004247:DNA; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D013254:Steroid 17-alpha-Hydroxylase