Article ID: b18-00729
Puerarin (daidzein 8−C−glucoside) is an isoflavone C−glucoside contained in the roots of Pueraria lobata Ohwi. We have previously isolated the human intestinal bacterium, strain PUE, which metabolizes puerarin to daidzein, though the enzyme which cleaves C−glycosidic bond has not been clarified. Here, we identified one of the intermediates of enzymatic puerarin C−deglycosylation reaction as 3″−oxo−puerarin (1): C−3 in the glucose moiety connecting to hydroxyl is oxidized to ketone group. 1 was easily isomerized to the mixture of 1, 2"−oxo−puerarin (2a) and cyclic acetal (2b) of 2a in non−enzymatic condition. We identified the putative puerarin−metabolizing operon of strain PUE composed of 8 genes (dgpA-H). Among them, DgpB−C complex was expressed in Escherichia coli, which cleaved the C−glycosidic bond in 1 but not puerarin. These results suggested that the puerarin C−deglycosylation reaction is a two−step enzymatic reaction, including the oxidation reaction at C−3" in puerarin to give 1, and the subsequent C−deglycosylation of 1 to provide daidzein.
