Partial purification and characterization of a novel soybean protease which is inhibited by Kunitz and Bowman-Birk trypsin inhibitors

A novel serine protease has been partially purified from dry seeds of the soybean (Glycine max) cultivar Keburi by cryoprecipitation at pH 6.4, fractional precipitation with ammonium sulfate, and a series of column chromatographic procedures on DEAE-Sepharose, SP-Sepharose, and Arginine-Sepharose 4B. Some properties of the purified enzyme were studied. The protease hydrolyzed the native storage globulins of soybean seeds, such as the alpha subunit of beta-conglycinin, at a pair of arginine residues, Arg126-Arg127. The proteolysis of the alpha subunit in the purified alpha 2 beta molecule of beta-conglycinin apparently followed first order kinetics. The enzyme was inhibited by both soybean Kunitz trypsin inhibitor and Bowman-Birk proteinase inhibitor in a competitive manner. Moreover, the enzyme could catalyze the specific proteolysis of the A3 polypeptide of the purified G5 glycinin at the Arg99-Gly100 linkage, or the carboxyl side of the Arg98-Arg99 paired basic residues.