Proteolysis of soybean bowman-birk trypsin inhibitor during germination

The Bowman—Birk type trypsin inhibitor, BBSTI-D, which appears in the cotyledons of germinated soybeans (Glycine max), was isolated in homogeneous form. BBSTI-D has an amino acid composition identical to the native Bowman—Birk soybean trypsin inhibitor (BBSTI-E) except for the loss of one glutamyl/glutaminyl residue and one aspartyl/asparaginyl residue. The amino-terminal sequence of BBSTI-D was identical to that of BBSTI-E. These data, as well as the compositions of the tryptic peptides from reduced carboxymethylated BBSTI-D, indicate that BBSTI-D is derived from BBSTI-E by the loss of the carboxyl-terminal residues Glu⁷⁰—Asn⁷¹.