Glycinin A₄A₅ Subunit Digesting Protease in Soybean Seeds

Abstract

Endopeptidase was partially purified from the globulin fraction of 4-hr-imbibed soybean seeds. The protease fraction obtained had proteolytic activity on the glycinin A₄A₅ subunit at both pH 4 and 8. A suitable peptidic substrate for the endopeptidase was isolated from the tryptic digest of the carboxymethylated A₄A₅ subunit. Using the tryptic peptide of glycinin A₅ subunit, a simple assay system for the soybean endopeptidase activity has been established. The activity was significantly inhibited by phenylmethylsulfonyl fluoride, indicating the endopeptidase is a serine protease.