抄録
3α-Hydroxyglycyrrhetinate dehydrogenase of Clostridium innocuum, isolated from human intestinal bacteria, was capable of converting 3-ketoglycyrrhetic acid to 3α-hydroxyglycyrrhetic acid. The enzyme was purified to homogeneity by means of butyl-Toyopearl 650M, Sephadex G-150, M_??_trex Red A, Toyopearl HW-55 S, and isoelectric focusing column chromatographies. The purified enzyme showed a specific activity of 156 μmol/min•mg toward 3α-hydroxyglycyrrhetic acid, and showed a single band on SDS-polyacrylamide gel electrophoresis. The apparent molecular weight was 53, 000, as estimated by gel filtration, and 30, 000, as judged by SDS-polyacrylamide gel electrophoresis. Its isoelectric point was 5.2. The enzyme showed absolute specificity for the 3α-hydroxyl and 3-ketonic groups of 18α- or 18β-glycyrrhetic acid and required NADP+ and NADPH as cosubstrates. The enzyme did not act on any 3α-hydroxyl or 3-ketonic group of steroids or bile acids. The enzyme is a novel type of enzyme, defined as 3α-hydroxy-glycyrrhetinate dehydrogenase, being quite different from 3α-hydroxysteroid dehy-drogenase [EC 1. 1. 1. 50].
