title: Active site-directed inhibition of rabbit cytochrome P-450 1 by amino-substituted steroids.
abstract: A variety of amino-substituted steroids were investigated as inhibitors of the rabbit hepatic, steroid 21-hydroxylase, cytochrome P-450 1. We reasoned that a steroid analog of pregnenolone capable of mimicking the binding of C21-steroids to the enzyme at the active site and bearing an amine moiety on the 17 beta-side chain would be a potent inhibitor if the amine were free to interact with the heme iron. Our studies reveal that 22-amino-23,24-bisnor-5-cholen-3 beta-ol (22-ABC) is a tightly-bound inhibitor of cytochrome P-450 1-catalyzed reactions (Ki less than 1 nM). Spectral differences elicited by 22-ABC indicate that when bound to the enzyme, the amine moiety of 22-ABC is coordinated to the heme iron. In contrast, several other hepatic cytochrome P-450s which mediate distinct regio-specific routes of metabolism for progesterone or pregnenolone remain largely unaffected at concentrations of 22-ABC that exceed by 2 orders of magnitude that required to inhibit cytochrome P-450 1. 22-ABC also inhibited the metabolism of benzo(a)pyrene attributable to cytochrome P-450 1 but did not inhibit that induced by treatment with rifampicin or 2,3,7,8-tetrachlorodibenzo-p-dioxin. Analogs of 22-ABC bearing a hydroxyl group or a methylamine in place of the amine moiety exhibit lower affinities for cytochrome P-450 1. In addition, either increasing or decreasing the number of carbons of the side chain reduced the affinity of the inhibitor for cytochrome P-450 1.
mesh_terms: D000818:Animals; D001564:Benzo(a)pyrene / Q000378:metabolism; D001665:Binding Sites / Q000187:drug effects; D055598:Chemical Phenomena; D002621:Chemistry; D065607:Cytochrome P-450 Enzyme Inhibitors; D004958:Estradiol / Q000378:metabolism; D008862:Microsomes, Liver / Q000201:enzymology*; D011283:Pregnenes / Q000494:pharmacology*; D011284:Pregnenolone / Q000378:metabolism; D011374:Progesterone / Q000378:metabolism; D011817:Rabbits; D013053:Spectrophotometry; D013329:Structure-Activity Relationship
chemical_list: D065607:Cytochrome P-450 Enzyme Inhibitors; D011283:Pregnenes; D001564:Benzo(a)pyrene; D011374:Progesterone; D004958:Estradiol; D011284:Pregnenolone; C046654:22-amino-23,24-bisnor-5-cholen-3-ol