Hydrolysis of Isoflavone Glycosides by a Thermostable β-Glucosidase from Pyrococcus furiosus

The recombinant beta-glucosidase from the hyperthermophilic archaeon Pyrococcus furiosus was purified with a specific activity of 330 U/mg for genistin by His-trap chromatography. The specific activity of the purified enzyme followed the order genistin > daidzin > glycitin> malonyl glycitin > malonyl daidzin > malonyl genistin. The hydrolytic activity for genistin was highest at pH 6.0 and 95 degrees C with a half-life of 59 h, a K-m of 0.5 mM, and a k(cat) of 6050 1/s. The enzyme completely hydrolyzed 1.0 mM genistin, daidzin, and glycitin within 100, 140, and 180 min, respectively. The soybean flour extract at 7.5% (w/v) contained 1.0 mM genistin, 0.9 mM daidzin, and 0.3 mM glycitin. Genistin, daidzin, and glycitin in the soybean flour extract were completely hydrolyzed after 60, 75, and 120 min, respectively. Of the reported beta-glucosidases, P. furiosus beta-glucosidase exhibited the highest thermostability, k(cat), k(cat)/K-m, yield, and productivity for hydrolyzing genistin. These results suggest that this enzyme may be useful for the industrial hydrolysis of isoflavone glycosides.