Enzymes Responsible for the Metabolism of Saikosaponins from Eubacterium sp. A-44,a Human Intestinal Anaerobe

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From a human intestinal bacterium, Eubacterium sp. A-44,which is capable of hydrolyzing saikosaponins to saikogenins, two glycosidases, β-D-glucosidase and a novel type of β-D-fucosidase, were isolated and characterized as saikosaponin-hydrolyzing β-D-glucosidase and prosaikogenin-hydrolyzing β-D-fucosidase.Relative to the hydrolyzing activities toward saikosaponins a, b_1 and b_2,the β-D-glucosidase showed lower ability to hydrolyze saikosaponin d, but no ability to hydrolyze saikosaponin c or prosaikogenins.By Sephacryl S-300 column chromatography, the molecular weight of prosaikogenin-hydrolyzing β-D-fucosidase was estimated to be about 130 kDa. The β-D-fucosidase could hydrolyze prosaikogenins A and F, but not prosaikogenins D and G or saikosaponins. Relative to p-nitrophenyl β-D-fucoside-hydrolyzing activity, this enzyme had 32.0% and 22.2% of its hydrolyzing ability toward p-nitrophenyl β-D-glucoside and p-nitrophenyl β-D-galactoside, respectively. p-Nitrophenyl β-D-fucoside-hydrolyzing activity was inhibited by D-fucose, and was weakly inhibited by D-glucose, D-glucono δ-lactone, D-galactose and D-galactono δ-lactone.By combining these two glycosidases, saikosaponins a and b_1 were converted to their saikogenins via the corresponding prosaikogenins.
公益社団法人日本薬学会の論文
1997-12-15