Epimerization of the 7-hydroxy group of bile acids by the combination of two kinds of microorganisms with 7 alpha- and 7 beta-hydroxysteroid dehydrogenase activity, respectively.
An unidentified gram-positive anaeroic organism capable of dehydrogenating the 7 beta-hydroxy group of ursodeoxycholic acid was recovered from human feces. By combined action of this organism with the ordinary 7 alpha-dehydrogenating bacteria, chenodeoxycholic acid and cholic acid alike were readily converted into their respective 7 beta-epimers and the reverse reactions were also carried out. The estimated levels of these 7 alpha- and 7 beta-dehydrogenating organisms among the intestinal microflora give a satisfactory explanation for the frequent appearance of the 7 beta-hydroxylated bile acids in vivo.
D000693:Anaerobiosis; D001419:Bacteria / Q000201:enzymology*; D001647:Bile Acids and Salts; D006913:Hydroxysteroid Dehydrogenases / Q000378:metabolism*; D007536:Isomerism; D007700:Kinetics
D001647:Bile Acids and Salts; D006913:Hydroxysteroid Dehydrogenases; C031932:7 beta-hydroxysteroid dehydrogenase; C025376:7 alpha-hydroxysteroid dehydrogenase