7 alpha-Dehydroxylation of bile acids by resting cells of a Eubacterium lentum-like intestinal anaerobe, strain c-25.

7 alpha-Dehydroxylation of cholic acid and chenodeoxycholic acid by whole cells of strain c-25, a Eubacterium lentum-like intestinal anaerobe, was studied. 7 alpha-Dehydroxylase activity was observed only in whole cells grown in the presence of the primary bile acid (cholic acid or chenodeoxycholic acid). Chenodeoxycholic acid was twice as effective as cholic acid as an inducer. Although cells grown in the presence of chenodeoxycholic acid had no significant substrate specificity for the two primary bile acids, cells grown in the presence of cholic acid showed two times greater activity against cholic acid than chenodeoxycholic acid. Exposure of cell suspensions to atmospheric oxygen resulted in little loss of the 7 alpha-dehydroxylase activity. The induced enzyme had an optimal pH range of 7.3 to 7.7. Although adding flavin mononucleotide to the growth medium significantly increased the 7 alpha-dehydroxylation of bile acids without an increase in cell growth, inhibition of the enzyme activity was observed in the resting cell system when flavin mononucleotide was included in the reaction mixture.