CHARACTERIZATION OF NADP+ - 3-BETA-HYDROXYSTEROID DEHYDROGENASE FROM MICROSOMES OF RAT-LIVER

A NADP +-dependent 3β-hydroxysteroid dehydrogenase activity was localized in the microsomal fraction of rat liver. This enzyme was solubilized and separated completely from 3α-hydroxysteroid dehydrogenase by Matrex red A column chromatography. Partially purified 3β-hydroxysteroid dehydrogenase catalyzed the oxidation and reduction between the 3β-hydroxyl and 3-ketonic group of steroids or bile acids having no double bond in the A/B ring, but was inactive toward 3α-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 43000 by Sephadex G-200 column chromatography. From these results, it is concluded that the enzyme is a new type of microsomal NADP +: 3β-hydroxysteroid dehydrogenase. © 1990.