title: Discriminatory inhibition of adrenocortical 17 alpha-hydroxylase activity by inhibitors of cholesterol side chain cleavage cytochrome P-450.
abstract: Two inhibitors of the cholesterol side chain cleavage reaction were tested for their ability to inhibit bovine adrenocortical 17 alpha-hydroxylase and 21-hydroxylase activities. One inhibitor, 22-amino-23,24-bisnor-5-cholen-3 beta-ol (22-ABC), was found to be a potent inhibitor of 17 alpha-hydroxylation of either progesterone or pregnenolone but was inactive on 21-hydroxylase activity. 22-ABC was found to be a competitive inhibitor of 17 alpha-hydroxylase (cytochrome P-45017 alpha) activity, having an apparent inhibitor constant of 29 nM when using pregnenolone as the substrate. Spectral binding studies showed that 22-ABC produces a type II difference spectrum when added to a bovine adrenocortical microsomal preparation, due presumably to a coordination of its amine nitrogen atom to the heme-iron of cytochrome P-45017 alpha. The second cholesterol side chain cleavage inhibitor tested, (20R)-20-phenyl-5-pregnene-3 beta,20-diol (20-PPD), was found not to inhibit either the 21- or 17 alpha-hydroxylase activities. It is proposed that the phenyl group projecting from C-20 of 20-PPD prevents this steroid from binding to cytochrome P-45017 alpha. The discriminatory interaction of these two steroids with adrenocortical cytochromes P-450 provides some insight with respect to possible structural features of the active-site regions of these enzymes.
mesh_terms: D000302:Adrenal Cortex / Q000201:enzymology*; D000818:Animals; D001665:Binding Sites; D002417:Cattle; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D011283:Pregnenes / Q000494:pharmacology; D013053:Spectrophotometry; D013254:Steroid 17-alpha-Hydroxylase / Q000037:antagonists & inhibitors*; D013250:Steroid Hydroxylases / Q000037:antagonists & inhibitors*
chemical_list: D011283:Pregnenes; C046654:22-amino-23,24-bisnor-5-cholen-3-ol; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D013254:Steroid 17-alpha-Hydroxylase