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Science 5 March 1982:
Vol. 215. no. 4537, pp. 1249 - 1251
DOI: 10.1126/science.7058343
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Articles

Science, Vol 215, Issue 4537, 1249-1251
Copyright © 1982 by American Association for the Advancement of Science

articles

Norethisterone, a major ingredient of contraceptive pills, is a suicide inhibitor of estrogen biosynthesis

Y Osawa, C Yarborough, and Y Osawa

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.




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Science. ISSN 0036-8075 (print), 1095-9203 (online)