The formation of glucosides of isoflavones and of some other phenols by rabbit liver microsomal fractions

Rabbit liver microsomal fractions in vitro effected the transfer of glucuronic acid from UDP-glucuronic acid to biochanin A, formononetin, daidzein, genistein and equol. Only monoglucuronides were formed. 2. The same isoflavones were converted into monoglucosides when UDP-[6-(3)H]glucose was substituted for UDP-glucuronic acid in the incubation medium in vitro. The glucosides were formed in much lesser yield than were the glucuronides. 3. The glucoside of genistein was identified as genistin (genistein 7-glucoside) by Sephadex chromatography and reverse isotope dilution. 4. The specificity of the glucuronyl- and glucosyl-transfer mechanisms was compared for a series of steroids and other phenols in addition to the isoflavones. It was concluded that separate transferases were responsible for the formation of the two types of glycosides.