초록
An ammonium sulfate precipitation of fermentation broth produced by Bacillus subtilis FBL-1 resulted in 2.9-fold increase of specific protease activity. An eluted protein fraction from the column chromatographies using DEAE-Cellulose and Sephadex G-75 had 94.2- and 94.9-fold higher specific protease activity, respectively. An SDS-PAGE revealed a band of purified protease at approximately 37.6 kDa. Although purified protease showed the highest activity at <TEX>$45^{\circ}C$</TEX> and pH 9.0, the activity remained stable in temperature range from 30 to <TEX>$50^{\circ}C$</TEX> and pH range from 7.0 to 9.0. Protease activity was activated by metal ions such as <TEX>$Ca^{2+}$</TEX>, <TEX>$Mg^{2+}$</TEX>, <TEX>$Mn^{2+}$</TEX>, <TEX>$Fe^{2+}$</TEX>, <TEX>$Ca^{2+}$</TEX> and <TEX>$K^+$</TEX>, but 10 mM <TEX>$Fe^{3+}$</TEX> significantly inhibited enzyme activity (53%). Protease activity was inhibited by 2 mM EDTA as a metalloprotease inhibitor, but it showed good stability against surfactants and organic solvents. The preferred substrates for protease activity were found to be casein (100%) and soybean flour (71.6%).