标题：Separation of 7 alpha- and 7 beta-hydroxysteroid dehydrogenase activities from clostridium absonum ATCC# 27555 and cellular response of this organism to bile acid inducers.
出版社：American Society for Biochemistry and Molecular Biology
摘要：Both 7 alpha- and 7 beta-hydroxysteroid dehydrogenases (HSDH) were induced by either chenodeoxy-(CDC) or deoxycholic (DC) acid in C. absonum. 7 beta-HSDH was partially purified 35-fold from CDC-induced cultures of C. absonum by Procion Red (PR) affinity chromatography and high performance liquid chromatography (HPLC) using a TSK 3000 SW gel filtration column. A relative molecular weight of 200 K was estimated for 7 beta-HSDH using Sephacryl S-300 chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of the 35-fold purified 7 beta-HSDH showed six polypeptides in the molecular weight range of 40-50 K. Induction of cultures of C. absonum with CDC or DC (0.4 mM) also resulted in the differential synthesis of at least five new polypeptides with molecular weights of 94 K, 42 K, 32 K, 21 K, and 16 K. The 16 K polypeptide was induced by DC but not by CDC. SDS-PAGE of Triton X-100-solubilized membranes from these extracts revealed the presence of a new membrane-associated polypeptide of molecular weight 80 K. The soluble inducible polypeptides were eliminated during purification of the 7 alpha- and 7 beta-HSDH and, therefore, are not required for these enzyme activities. It is proposed that this organism synthesized 7 alpha- and 7 beta-HSDH as well as a series of other proteins in response to bile acids which may, in the absence of the dehydrogenases, be toxic to C. absonum. The HSDH's catalyze the epimerization of chenodeoxycholic acid to ursodeoxycholic acid, which is less toxic than the chenodeoxycholic acid. The other proteins may assist the survival of the organism in a high bile acid environment by mechanisms not yet understood.
