Purification and some properties of soybean saponin hydrolase from Aspergillus oryzae KO-2

We had investigated the enzymatic hydrolysis of soybean saponins and selected soybean saponin hydrolase from Aspergillus oryzae KO-2. We attempted purification of this enzyme for further characterization. This enzyme was purified 1500-fold using ammonium sulfate fractionation and Sephadex G-200 gel filtrations. The enzyme was electrophoretically homogeneous and a glycoprotein by PAS staining. By gel filtration, the molecular weight of enzyme was 158,000 and SDS-PAGE showed the enzyme to have a tetrameric structure composed of heterogeneous subunits of 35,000 and 45,000. The enzyme activity was stable at temperatures below 40 degrees C and stable from pH 5.0 to 8.0. The optimum pH was pH 4.5 to 5.0 and the optimum temperature was 50 degrees C. The Km and Vmax for soyasaponin I were 0.48 mM and 9.8 mumol/hr mg protein, respectively. After hydrolysis with the enzyme, soyasapogenol B and alpha-L-rhamnopyranosyl (1----2)-beta-D-galactopyranosyl (1----2)-D-glucuronopyranoside were released from soyasaponin I.