7β-Dehydroxylation of ursodeoxycholic acid by whole cells and cell extracts of the intestinal anaerobic bacterium, Eubacterium species V.P.I. 12708

Bryan A White, R. J. Fricke, P. B. Hylemon

Research output: Contribution to journalArticle

Abstract

Whole cells and cell extracts of Eubacterium species V.P.I. 12708 7-dehydroxylated [3H]ursodeoxycholic acid or [14C]chenodeoxycholic forming lithocholic acid. 7β-Dehydroxylation specific activity was 146 and 386 nmol hr-1 mg protein -1 for cell extracts and whole cells, respectively. 7α- or 7β-Dehydroxylation activity was detected only in whole cells or cell extracts prepared from cultures grown in the presence of cholic acid. The addition of NAD+ (0.5 mM) to anaerobically dialyzed cell extracts stimulated 7β- and 7α-dehydroxylation activity by 5- and 40-fold, respectively. The level of 7β-dehydroxylation specific activity was approximately 3- to 5-fold lower than 7 α-dehydroxylation in whole cells and 3-fold lower in cell extracts. Substrate saturation kinetics for ursodeoxycholic acid and chenodeoxycholic acid were hyperbolic and showed substrate inhibition at concentrations above 200 μM. The apparent K(m) values for ursodeoxycholic and chenodeoxycholic acid were 14.5 μM and 49 μM, respectively. Both 7α- and 7β-dehydroxylase activities were inactivated (60% to 70%) by heating for 6 min at 45°C. Moreover, both activities co-eluted from a anaerobic Bio-Gel A 1.5-M column as a single peak at approximately 114,000 (M(r)). These data show that this intestinal anaerobic bacterium has both 7α- and 7β-dehydroxylase activities which may be catalyzed by the same enzyme.

Original languageEnglish (US)
Pages (from-to)145-153
Number of pages9
JournalJournal of Lipid Research
Volume23
Issue number1
StatePublished - Dec 1 1982

ASJC Scopus subject areas

  • Biochemistry
  • Endocrinology
  • Cell Biology

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