Chemical substitutions of the reactive site leucine residue in soybean Bowman-Birk proteinase inhibitor with other amino acids.

A method of exchanging amino acid residue (P1 residue) which determines primarily the inhibitory specificity of a proteinase inhibitor is described. Leu43 (P1 residue) at the chymotrypsin reactive site of Bowman-Birk soybean inhibitor was removed by limited proteolysis of Leu43-Ser44 bond followed by carboxypeptidase digestion. An appropriate amino acid methyl ester was introduced into this position by water-soluble carbodiimide. Derivatives having methyl esters of Gly, Ala, Val, Met, Leu, Phe, Trp, or D-Trp at position 43 were prepared and were shown to restore the activity to various extents. This method provides new approach to study structure-function relationship of proteinase inhibitors and to prepare novel inhibitors.