Amino acid sequence of the acidic Kunitz-type trypsin inhibitor from winged-bean seed [Psophocarpus tetragonolobus (L.) DC].

The primary sequence of trypsin inhibitor-2 (WBTI-2) from Psophocarpus tetragonolobus (L.) DC seeds was determined. This inhibitor consists of a single polypeptide chain of 182 amino acids, including four half-cystine residues, and an N-terminal residue of pyroglutamic acid. The sequence of WBTI-2 showed 57% identity to the basic trypsin inhibitor (WBTI-3) and 50% identity to the chymotrypsin inhibitor (WBCI) of winged bean, and 54% identity to the trypsin inhibitor DE-3 from Erythrina latissima seed. The similarity to the soybean Kunitz trypsin inhibitor (40%) and the other Kunitz-type inhibitors from Adenanthera pavonina (30%) and wheat (26%) was much lower. Sequence comparisons indicate that the Psophocarpus and Erythrina inhibitors are more closely related to each other than to other members of the Kunitz inhibitor family.