Amino acid sequences of double-headed proteinase inhibitors from the seeds of Canavalia lineata.

The amino acids of two Bowman-Birk type proteinase inhibitors (CLTI-I and -II) from the seeds of Canavalia lineata were sequenced by a manual Edman degradation using the DABITC/PITC double coupling method after enzymatic digestions with Achromobacter lyticus lysyl endopeptidase, Staphylococcus aureus V8 protease, and chymotrypsin. CLTI-I contains 75 amino acid residues. CLTI-II has an identical sequence to CLTI-I except an extra Asp residue attached at the C-terminus. The inhibitors showed a homology (40-70%) to other Bowman-Birk inhibitors. The reactive-site peptide bonds were estimated to be Lys21-Ser22 and Leu48-Ser49 against trypsin and chymotrypsin, respectively. An inhibitory active fragment containing only the chymotrypsin-reactive site was also described.