Reduction of C19‐, C21‐, C24‐, and C27,‐3‐Oxosteroids by Rat‐Liver Microsomes

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Abstract
The reduction of various C19, C21, C24, and C27‐3‐oxosteroids by rat liver microsomes was studied. Large variations were observed in the relative rates of 3α and 3β reduction of the 3‐oxo‐steroids. Variations were also observed in the degree of stimulation by NADH and NADPH. Except for C27‐3‐oxosteroids, the ratio between the 3α‐ and 3β‐hydroxy derivative formed was higher with microsomes from female rats than than with those from male rats. The 3α‐ and 3β‐hydroxysteroid dehydrogenase activities showed a specificity towards the 4B‐hydrogen of NADH. Experiments with different inhibitors, with partially inactivated microsomes and with partially purified Triton extracts of microsomes indicate the presence of several different 3α‐ and 3β‐hydroxysteroid dehydrogenases in rat liver microsomes with different specificities towards NADH and NADPH and with overlapping substrate specificities.