3β-Hydroxysteroid Dehydrogenase of Ruminococcus sp. from Human Intestinal Bacteria

Abstract

Ruminococcus sp. PO1-3 obtained from human intestinal flora is able to reduce dehydrocholate as well as 3-ketoglycyrrhetinate. From this bacterium dehydro-cholate- and 3-ketoglycyrrhetinate-reducing activities were purified one thousandfold together with 3-ketocholanate-reducing and 3β-hydroxyglycyrrhetinate (glycyrrhetic acid) oxidizing activities by means of M_??_trex Red A, Sephadex G-200 and Octyl-Sepharose column chromatography. The purified enzyme catalyzed the reduction of dehydrocholic acid to 3β-hydroxy-7, 12-diketocholanic acid and of 3-ketocholanic acid to 3β-hydroxycholanic acid. Studies on substrate specificity revealed that the enzyme had absolute specificity for the β-configuration of a hydroxyl group at the 3 position of bile acid and steroids having no double bond in the A/B ring. This enzyme was neither β-hydroxysteroid dehydrogenase [EC 1.1.1.51] nor 3β-hydroxy-Δ⁵-steroid dehydrogenase [EC 1.1.1.145], but a novel type of enzyme, defined as 3β-hydroxysteroid dehydrogenase.