Estradiol 17 beta-dehydrogenase and 20 alpha-hydroxysteroid dehydrogenase from human placental cytosol: one enzyme with two activities?

The soluble enzyme estradiol 17 beta-dehydrogenase (17 beta-ED) from human term placental cytosol is reported to be a stereospecific oxidoreductase for estrogen substrates. A published purification scheme (heat treatment and affinity chromatography) yielded a homogeneous protein which had the reported characteristics of pure 17 beta-ED and also had 20 alpha-hydroxysteroid dehydrogenase (20 alpha-HSD) activity. Spectrophotometric assay when the buffer contained albumin, 8 mg/ml, masked the 20 alpha-HSD activity observed in albumin-free conditions and may explain why this bifunctional activity has gone unrecognized. In human placenta, one enzyme may catalyze stereospecific oxidation/reduction of both estrogen and progesterone.