Enzymatic formation of a cholic acid derivative of isethionic acid

Evidence is presented that preparations of rat liver microsomes are capable of conjugating isethionic acid with cholic acid. Thin-layer chromatography experiments indicate that this newly described conjugated bile acid migrates with the same Rf value as taurocholic acid, a structurally similar analogue. Dilution experiments utilizing both labeled cholic acid (tritium) and isethionic acid (sulfur-35) demonstrate the incorporation of both isotopes into a cholyl-conjugate of isethionic acid. Acid hydrolysis of enzymatically synthesized cholyl[35]isethionic acid and subsequent thin-layer chromatography of the degradation products also indicate that isethionic acid is conjugated with cholic acid. Formation of the cholyhydrazide derivative of cholyl-isethionic acid confirms an ester linkage between the carboxyl moiety of cholic acid and the hydroxyl moiety of isethionic acid. Rats receiving radioactive isethionic acid by stomach tube synthesized approximately 28 nmoles cholyl-isethionic acid compared with 980 nmoles taurocholic acid when radioactive taurine was administered under similar conditions.