Two neutral steroid-transforming activities were demonstrated in cell extracts of Clostridium scindens . Steroid-17–20-desmolase and 20α-hydroxysteroid dehydrogenase were found to be inducible in cells cultured in the presence of Cortisol. Both activities required manganese ions and NAD + or NADH for activity. Cortisol, cortisone and 11-desoxycortisol were substrates as well as induce of steroid-17–20-desmolase and 20α-hydroxysteroid dehydrogenase activities. 17α-Hydroxyprogesterone was an effective inducer but did not serve as a substrate for either enzyme activity. C. scindens is the first bacterial species of the normal human intestinal flora reported to elaborate inducible steroid-17–20-desmolase and 20α-hydroxysteroid dehydrogenase activities. The results of cofactor, substrate specificity and induction studies suggest that these two activities may reside in the same enzyme complex.
The conversion of progesterone to 20α-hydroxy-4-pregnen-3-one by 20α-hydroxysteroid dehydrogenase was measured in mouse vaginal tissue. The enzyme was confined to the 105,000 × g supernatant of tissue homogenates and the requirement for reduced NADP demonstrated. The Initial rates of 20α-hydroxysteroid dehydrogenase were determined in the cytosol of tissues from four-day estrogen-treated and untreated animals. The rate of 20α-hydroxy-4-pregnen-3-one formation per vagina was increased 15-fold by estrogen stimulation. This increase could not be accounted for on the basis of increased organ weight or increased availability of cofactor. These findings indicate that 20α-hydroxy steroid dehydrogenase induction in the mouse vaginae is under estrogen control.