Biol. Pharm. Bull. 28(9) 1672—1678 (2005)

are more resistant towards acid, alkaline and enzyme hydrolysis than O-glucosides. Even prolonged exposure to acid does not cleave the glucosyl bond of C-glucosides, in which glucose is attached by a carbon–carbon bond to the aglycone, to give the aglycone. However, intestinal bacteria from human feces can cleave C-glucosyl bonds in various C-glucosides such as mangiferin, abrusin 2 -O-b-D-apioside, aloeresin A, aloesin, barbaloin, bergenin, homoorientin, puerarin and safflor yellow B. Mangiferin (2-b-D-glucopyranosyl-1,3,6,7-tetrahydroxyxanthone), was originally isolated from Mangifera indica L. (Anacardiaceae). It is distributed among at least sixteen plant families including Anacardiaceae, Iridaceae and Gentianaceae. Studies in vitro have shown that mangiferin has antiviral activity against herpes simplex virus as well as antioxidant, and anti-HIV activity. Mangiferin orally administered to rats or mice exerts biological antitumor, antidiabetic, antioxidant, hepatoprotective and immunomodulative activities. However, the pharmacokinetic studies in rats given oral mangiferin have failed to detect mangiferin in plasma, suggesting poor absorption. On the other hand, appreciable amounts of euxanthone (1,7-dihydroxyxanthone) and its glucuronides are excreted into the urine of rabbits given oral mangiferin, indicating a unique metabolic transformation that involves elimination of a Cglucosyl chain and two phenolic hydroxyl groups. The transformation of mangiferin to norathyriol by human fecal flora in vitro (Fig. 1) indicates an important role of mangiferinmetabolizing bacteria in the disposition of norathyriol and its subsequent metabolites in vivo, as well as in the pharmacological activities of mangiferin. Norathyriol also exerts antiinflammatory, vasorelaxation and antiplatelet activities. Therefore, the biotransformation of mangiferin should be thoroughly investigated. Here, we isolated and characterized a bacterium that transforms mangiferin to norathyriol. Furthermore, the novel enzyme that cleaved C-glucosyl was selectively inducible with mangiferin and apparently differs from aand b-glucosidases.