Human gut bacterium Dorea sp. MRG-IFC3 is unique in that it only metabolizes puerarin, an isoflavone C-glycoside, whereas it shows broad substrate glycosidase activity for the various flavonoid Oglycosides. To address the question on the substrate specificity, as well as biochemical characteristics, cell-free biotransformation of flavonoid glycosides was performed under various conditions. The results showed that there are two different enzyme systems responsible for the metabolism of flavonoid C-glycosides and O-glycosides in the MRG-IFC3 strain. The system responsible for the puerarin conversion was inducible and comprised of two enzymes; one oxidizes puerarin to 3"-oxopuerarin and the other converts 3"-oxo-puearin to daidzein. The second enzyme was only active toward 3"-oxo-puerarin. The activity of puerarin conversion to daidzein was enhanced in the presence of Mn+2 and NAD+ . It was concluded that puerarin C-deglycosylation by Dorea sp. MRG-IFC3 possibly adopts the same biochemical mechanism as the strain PUE, a species of Dorea longicatena.
Keywords: C-C bond cleavage; Dorea sp. MRG-IFC3; flavonoid glycoside; puerarin.