PARTIAL-PURIFICATION AND CHARACTERIZATION OF A NOVEL SOYBEAN PROTEASEWHICH 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 co lumn chromatographic procedures on DEAE-Sepharose, SP-Sepharose, and A rginine-Sepharose 4B. Some properties of the purified enzyme were stud ied. The protease hydrolyzed the native storage globulins of soybean s eeds, such as the alpha subunit of beta-conglycinin, at a pair of argi nine residues, Arg126-Arg127. The proteolysis of the alpha subunit in the purified alpha(2) beta molecule of beta-conglycinin apparently fol lowed first order kinetics. The enzyme was inhibited by both soybean K unitz trypsin inhibitor and Bowman-Birk proteinase inhibitor in a comp etitive manner. Moreover, the enzyme could catalyze the specific prote olysis of the A3 polypeptide of the purified G5 glycinin at the Arg99- Gly100 linkage, or the carboxyl side of the Arg98-Arg99 paired basic r esidues.