7alpha-Dehydroxylation of cholic acid and chenodeoxycholic acid by Clostridium leptum.

E J Stellwag,P B Hylemon

doi:10.1016/s0022-2275(20)40615-7

Abstract

The rate of 7alpha-dehydroxylation of primary bile acids was quantitatively measured radiochromatographically in anaerobically washed whole cell suspensions of Clostridium leptum. The pH optimum for the 7alpha-dehydroxylation of both cholic and chenodeoxycholic acid was 6.5-7.0. Substrate saturation curves were observed for the 7alpha-dehydroxylation of cholic and chenodeoxycholic acid. However, cholic acid whole cell K0.5 (0.37 micron) and V (0.20 mumol hr-1mg protein-1) values differed significantly from chenodeoxycholic acid whole cell K0.5 (0.18 micron) and V (0.50 mumol-1 hr-1 mg protein-1). 7alpha-Dehydroxylation activity was not detected using glycine and taurine-conjugated primary bile acids, ursodeoxycholic acid, cholic acid methyl ester, or hyocholic acid as substrates. Substrate competition experiments showed that cholic acid 7 alpha-dehydroxylation was reduced by increasing concentrations of chendeoxycholic acid; however, chenodeoxycholic acid 7alpha-dehydroxylation activity was unaffected by increasing concentrations of cholic acid. A 10-fold increase in cholic and 7alpha-dehydroxylation activity occurred during the transition from logarithmic to stationary phase growth whether cells were cultured in the presence or absence of sodium cholate. In the same culture, a similar increase in chenodeoxycholic acid 7alpha-dehydroxylation was detected only in cells cultured in the presence of sodium cholate. These results indicate the possible existence of two independent systems for 7alpha-dehydroxylation in C. Leptum.

Highlights

T h e rate of 7a-dehydroxylation of primary bile acids was quantitatively measured radiochromatographically in anaerobically washed whole cell suspensions of Clostridium leptum
The most important bacterial modification of the primary bile acids cholic acid and chenodeoxycholic acid is 7-a-dehydroxylation which results in the formation of the secondary bile acids deoxycholic acid and lithocholic acid, respectively [2]
Aries and Hill (1 1) reported that 7a-dehydroxylase is widespread in most species o f the predominant human intestinal microflora. The explanation for this discrepancy is not yet clear. In this communication we report the characterization of 7a-dehydroxylation activity in whole cells of Clostridium leptum using both cholic acid and chenodeoxycholic acid as substrate

Summary

Introduction

T h e rate of 7a-dehydroxylation of primary bile acids was quantitatively measured radiochromatographically in anaerobically washed whole cell suspensions of Clostridium leptum. 7a-Dehydroxylation activity was not detected using glycine- and taurine-conjugated primary bile acids, ursodeoxycholic acid, cholic acid methyl ester, or hyocholic acid as substrates. A similar increase in chenodeoxycholic acid 7a-dehydroxylation was detected only in cells cultured in the presence of sodium cholate. These results indicate the possible existence of two independent systems for 7a-dehydroxylation in C. The most important bacterial modification of the primary bile acids cholic acid and chenodeoxycholic acid is 7-a-dehydroxylation which results in the formation of the secondary bile acids deoxycholic acid and lithocholic acid, respectively [2].

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