Characterization of NADP+: 3 beta-hydroxysteroid dehydrogenase from microsomes of rat liver.

A NADP(+)-dependent 3 beta-hydroxysteroid dehydrogenase activity was localized in the microsomal fraction of rat liver. This enzyme was solubilized and separated completely from 3 alpha-hydroxysteroid dehydrogenase by Matrex red A column chromatography. Partially purified 3 beta-hydroxysteroid dehydrogenase catalyzed the oxidation and reduction between the 3 beta-hydroxyl and 3-ketonic group of steroids or bile acids having no double bond in the A/B ring, but was inactive toward 3 alpha-hydroxyl group. The enzyme required NADP+ for oxidation and NADPH for reduction. The activity was inhibited by p-chloromercuribenzoic acid or p-chloromercuribenzenesulfonic acid at the concentration of 10(-4) M. The molecular weight of the enzyme was estimated to be about 43,000 by Sephadex G-200 column chromatography. From these results, it is concluded that the enzyme is a new type of microsomal NADP+:3 beta-hydroxysteroid dehydrogenase.