Primary structure of Kunitz-type trypsin inhibitor-2a (pI 5.9) from Psophocarpus tetragonolobus (L.) DC seed

The primary structure of acidic trypsin inhibitor-2a (WBTI-2a, pI 5.9) from Psophocarpus tetragonolobus (L.) DC seed was determined. This inhibitor consists of a single polypeptide chain of 180 amino acids including four half-cystine residues and has an N-terminal residue of pyroglutamic acid. The sequence of WBTI-2a, pI 5.9, showed 84% identity to acidic trypsin inhibitor-2 (WBTI-2, pI 5.1) but only 57% identity to the basic trypsin inhibitor (WBTI-1, pI 8.9) and 50% identity to the chymotrypsin inhibitor of winged bean. The data indicate that winged bean seed contains a family of three Kunitz-type inhibitors which have about 50% identity.