The possibility of the double head of leguminous STI(Kunitz) family inhibitors.

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1) The complete amino acid sequence of winged bean chymotrypsin inhibitor 3 (WCI-3) was determined by the conventional methods. WCI-3 consisted of 183 amino acid residues, but was heterogeneous in the carboxyl terminal region. The sequence of WCI-3 was highly homologous with those of STI(Kunitz) family inhibitors.2) WCI-3 was treated with porcine chymotrypsin at pH 3.0. Chymotrypsin, however, hydrolyzed only the first reactive site (Leu(65)-Ser(66)). Onthe trial to cleave the second reactive site oF WCI-3 using several chymotrypsin-family enzymes, elastase, subtilisin, SGPS and SGPB, no enzyme could cleave the peptide bond of the second reactive site. The similar studies were done using the soybean trypsin inhibitor (Kunitz) (STI) Ti^a. The results suggested that the second reactive site of Ti^a might be located at or near Met(84)-Leu(85).