Homology among trypsin/chymotrypsin inhibitors from red kidney bean, Brazilian pink bean, lima bean, and soybean

Abstract

Three trypsin/chymotrypsin inhibitors [R(A), R(B2), R(C)] from red kidney bean (RKB; Phaseolus vulgaris var. Linden) and three [B(A), B(B), B(C)] from Brazilian pink bean (BPB; P. vulgaris var. Rosinha G2) inhibited one trypsin and one chymotrypsin/mol simultaneously. One RKB inhibitor [R(B1)] inhibited one trypsin/mol. Dissociation constants of trypsin- and chymotrypsin-inhibitor complexes ranged from 0.48 to 5.37 nM. High homology was shown among the seven inhibitors by tryptic and chymotryptic peptide maps by using anion-exchange and reverse-phase chromatographies. The inhibitors also showed significant homology with lima bean and soybean Bowman-Birk inhibitors but not with soybean Kunitz inhibitor. The N-terminal 16 amino acid sequence of inhibitor B(B) showed high homology with several Bowman-Birk inhibitors. A convenient peptide mapping procedure especially suitable for cysteine-rich proteinase inhibitors and analysis of peptide mapping data are described. The procedure and data analysis method provide an approach to assess homology among proteins without sequence data.