title: Norethisterone, a major ingredient of contraceptive pills, is a suicide inhibitor of estrogen biosynthesis.
abstract: Norethisterone (17 alpha-ethynyl-19-nortestosterone) is an effective irreversible inhibitor of estrogen synthetase (aromatase), the enzyme responsible for the conversion of androgens to estrogens, even at a 2 X 10(-6) molar concentration. This irreversible inactivation, which is directed toward the active site of aromatase and requires the cofactor-reduced nicotinamide adenine dinucleotide phosphate, is both time- and concentration-dependent. Ethisterone (17 alpha-ethynyltestosterone), in contrast, is not a suicide inhibitor of aromatase even at concentrations of 10(-4) molar.
mesh_terms: D047072:Aromatase Inhibitors; D001665:Binding Sites / Q000187:drug effects; D003276:Contraceptives, Oral / Q000494:pharmacology*; D004967:Estrogens / Q000096:biosynthesis*; D005260:Female; D006801:Humans; D007700:Kinetics; D008861:Microsomes / Q000201:enzymology; D009640:Norethindrone / Q000494:pharmacology*; D010088:Oxidoreductases / Q000037:antagonists & inhibitors*; D010920:Placenta / Q000201:enzymology; D011247:Pregnancy
chemical_list: D047072:Aromatase Inhibitors; D003276:Contraceptives, Oral; D004967:Estrogens; D010088:Oxidoreductases; D009640:Norethindrone