Active site-directed irreversible inhibition of 3 beta-hydroxysteroid dehydrogenase from human placenta

To obtain a placental microsome preparation able to convert androstenedione and testosterone specifically to estrogens, 3 beta-hydroxysteroid dehydrogenase must be eliminated. After solubilisation by Triton X-100, the remaining 3 beta-hydroxysteroid dehydrogenase activity is inhibited by 11 alpha-bromoacetoxyprogesterone, an alkylating analogue of progesterone, which behaves as an irreversible active site-directed inhibitor. The enzyme is protected against inactivation and alkylation by steroid and coenzyme substrates. The inhibition is specific to 3 beta-hydroxysteroid dehydrogenase and the estrogen synthetase (aromatase) activity contained in the preparation is not affected by this inhibitor.