Studies on Soybean Trypsin Inhibitors

Abstract

Soybean trypsin inhibitor (Kunitz) was divided into four peptide fragments by the combination of limited hydrolysis with trypsin at acidic pH, chemical cleavage of methionyl bonds with cyanogen bromide, and reduction and carboxymethylation of disulfides in protein or peptide. Each fragment was separated and purified by gel filtration on Sephadex G‐50, G‐75 or G‐100, and referred to as fragments A, B, C, and D from the amino‐ to the carboxyl‐terminal region of the inhibitor. Soybean trypsin inhibitor (Kunitz) consisted of 181 amino acid residues and its molecular weight was proved to be 20100. Fragments A, B, C, and D consisted of 63, 21, 30, and 67 amino acid residues, respectively. One of the two disulfide bridges in the inhibitor was involved in fragment D, and the other linked fragment A with fragment C.