Somemicroorganisms, including somebacteria isolated from soil, were found to secrete an extracellular soymilk-clotting enzyme. Amongthem, strain No. K-295G-7showedthe highest soymilk-clotting activity and stability of the production of the soymilk-clotting enzyme. The enzyme system (culture filtrate) coagulated protein in soymilk, a curd being formed at pH 5.8~6.7 and at 55~75°C. The optimum temperature for the soymilk-clotting activity was 75°C and the enzyme system was stable at temperatures below 50°C downto 35°C. About 80~100%of the original activity remained after 1 hr at pH 5~7 and 35°C.

Enzymes I and II, which have a high soymilk-clotting activity, produced from K-295G-7 were purified by chromatographies on Sephadex G-100, CM-cellulose, hydroxylapatite, and 2nd Sephadex G-100. The two purified enzymes were found to be homogeneous by polyacrylamide gel electrophoresis (PAGE) at pH 4.3. The molecular weights ofenzymes I and II were 28,000 and 29,500 by SDS-PAGE, and their isoelectric points were 9.22 and 9.45, respectively. Enzymes I and II coagulated soymilk optimally at 65°C and were stable up to 45°C. Both enzymes were most active at pH 5.8, for soymilk coagulation between pH 5.8 to 6.7, and were stable with about 50~100% of the original activity from pH 5 to 10. Each of the purified enzymes was a serine protease with an optimum pH of9.0 for soy protein isolate (SPI) and casein digestions, because these enzymes were inhibited completely by diisopropylfluoro-phosphate (DFP). The soymilk-clotting activity to proteolytic activity ratio of the enzyme II was 3 times higher than that of enzyme I. Enzymes I and II were more sensitive to the calcium ion concentration in soymilk than bromelain is. Soybean contains useful human nutrients such as proteins, lipids and sugars. Soybean

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