Most of legume seeds contain serveral kinds of BBI-type inhibitors. They have similar amino acid residues around the reactive site. The P₁ site amino acid residue in reactive site generally corresponds to the specificity of the cognate enzyme. It ha...
Most of legume seeds contain serveral kinds of BBI-type inhibitors. They have similar amino acid residues around the reactive site. The P₁ site amino acid residue in reactive site generally corresponds to the specificity of the cognate enzyme. It has also been noted the importance of P₁ site amino acid residue in synthetic cyclic nonapeptide derivatives which were related to active site of BBI. To obtain further understanding of the role of amino acid residues near th reactive site, 3 cyclic nonapeptides which are substituted analogues of GBI-II were synthesized and the inhibition constants for some proteinases were calculated by Dixon method. Antielastic fragment in GBI-II (I_a) differ only P₂ Site with that of soybean isoinhibitor C-II, Ki of Ia for porcine pancreatic elastase was 48μM, Ki of antitryptic fragment in LBI (I_b) for trypsin was 3.7μM, and Tyr analogue (I_c) for chymotrypsin showed no inhibition but appeared low inhibitory activity for trypsin and elastase. To elucidate the relation between loop size and inhibitory activity, 3 cyclic pentapeptide analogues containing the each reactive site of Ala-Ser, Lys-Ser and Tyr-Ser were synthesized. These peptides possessed slight inhibitory activity toward proteinases, Ki of synthetic cyclic pentapeptides for elastase, trypsin, and chymotrypsin were 614μM, 278μM and 128μM, respectively.