Studies on the inhibitory mechanism of soybean trypsin inhibitors by the chemical change of amino acid residues.

胰蛋白酶抑制剂可以通过混合通过相互交换从两种酶促修饰的大豆胰蛋白酶抑制剂分离的蛋白质部分和肽部分（从位置64至位置84）来重构。在62位具有酪氨酸和在71位具有组氨酸的重构抑制剂显示出最高的抑制活性，Ki值约为10 μ <-10>M。在62和71位分别具有苯丙氨酸和天冬酰胺的抑制剂显示出最弱的抑制活性，Ki值约为10 μ <-8>M。在第62位具有酪氨酸或在第71位具有组氨酸的抑制剂具有约10 μ M的Ki值<-9>。通过混合蛋白质部分和合成肽来重构其它抑制剂。将74位丝氨酸残基替换为精氨酸，将84位蛋氨酸替换为蛋氨酸亚砜，对Ki值没有影响，表明它们与胰蛋白酶的接触没有直接关系。当蛋白质部分与缺乏His（71）、Pro（72）和Leu（73）残基的合成肽混合时，未观察到抑制活性。

Trypsin inhibitors could be reconstituted by mixing the protein moieties and the peptide moieties (from position 64 to position 84) separated from two enzymatically modified soybean trypsin inhibitors by the mutual exchange. A reconstituted inhibitor which has tyrosine at position 62 and histidine at position 71 showed the highest inhibitory activity with Ki value of approximately 10^<-10> M. An inhibitor having phenylalanine and asparagine at positions 62 and 71, respectively, showed the weakest inhibitory activity with Ki value of about 10^<-8> M. Inhibitors possessing either tyrosine at position 62 or histidine at position 71 had Ki value of about 10^<-9> M. Other inhibitors were reconstituted by mixing the protein moieties and synthetic peptides. The replacements of serine residue at position 74 to arginine, and methionine at position 84 to methionine sulfoxide did not affect on Ki values, indicating that they are not concerned directly in contacting with trypsin. No inhibitory activity was observed when the protein moieties were mixed with a synthetic peptide lacking His(71), Pro(72) and Leu(73) residues.