[In vitro aromatization of androgens in the presence of testosterone binding proteins from human placenta or serum].

Two related 17 beta hydroxy steroid binding proteins of serum and placental origin respectively are shown to inhibit significantly the aromatization of testosterone and androstenedione by isolated human placenta microsomes. Quantitative correlations suggest that this inhibitory effect is due to the fixation of the testosterone substrate (or androstenedione previously converted to testosterone) on the binding proteins. A possible role for these macromolecules in the steroidogenic activity of the placenta is discussed.