title: Steroid 16 alpha-hydroxylase from human fetal liver; inhibition by steroids.
abstract: The 16 alpha-hydroxylase system in fetal liver which used dehydroepiandrosterone (DHA) or pregnenolone as substrate, was apparently inhibited by various endogenous and synthetic steriods: DHA, pregnenolone, their sulfates, androstenediol, androstenetriol, estrone, estradiol-17 beta, ethynylestradiol and chlormadinone-acetate. The inhibition constants (Ki) towards DHA were as follows; pregnenolone 22 muM, DHA-sulfate 13 muM, pregnenolone-sulfate 21 muM, androstenediol 16 muM, androstenetriol 53 muM estrone 32 muM, estradiol-17 beta 74 muM, ethynylestradiol 22 muM and chlormadinone-acetate 27 muM. The Ki values towards pregnenolone were DHA 6.3 muM, DHA-sulfate 8.3 muM, pregnenolone-sulfate 3.9 muM, androstenediol 8.7 muM, androstenetriol 14.7 muM, estradiol-17 beta 15.4 muM and ethynylestradiol 16.0 muM, respectively. The reaction products, 16 alpha OH-DHA and 16 alpha OH-pregnenolone, showed little inhibitory effect upon the 16 alpha-hydroxylase.
mesh_terms: D006907:17-alpha-Hydroxypregnenolone / Q000378:metabolism; D000734:Androstenediols / Q000494:pharmacology; D000737:Androstenols / Q000494:pharmacology; D001189:Aryl Hydrocarbon Hydroxylases; D002715:Chlormadinone Acetate / Q000494:pharmacology; D003687:Dehydroepiandrosterone / Q000494:pharmacology; D004958:Estradiol / Q000494:pharmacology; D004970:Estrone / Q000494:pharmacology; D004997:Ethinyl Estradiol / Q000494:pharmacology; D006801:Humans; D008099:Liver / Q000196:embryology / Q000201:enzymology*; D008656:Mestranol / Q000494:pharmacology; D009640:Norethindrone / Q000494:pharmacology; D011284:Pregnenolone / Q000494:pharmacology; D011374:Progesterone / Q000494:pharmacology; D039181:Steroid 16-alpha-Hydroxylase; D013250:Steroid Hydroxylases / Q000378:metabolism* / Q000494:pharmacology*
chemical_list: D000734:Androstenediols; D000737:Androstenols; D002715:Chlormadinone Acetate; D004970:Estrone; D006907:17-alpha-Hydroxypregnenolone; D004997:Ethinyl Estradiol; D003687:Dehydroepiandrosterone; D011374:Progesterone; D004958:Estradiol; D011284:Pregnenolone; D008656:Mestranol; D013250:Steroid Hydroxylases; D001189:Aryl Hydrocarbon Hydroxylases; D039181:Steroid 16-alpha-Hydroxylase; D009640:Norethindrone