Studies on Soybean Trypsin Inhibitors

For the elucidation of amino acid sequence around the reactive site of soybean trypsin inhibitor (Kunitz), fragments A and B were digested with trypsin, and the resulting peptides were separated by ion‐exchange chromatography on Dowex 50X2 or by gel filtration on Bio‐Gel P‐4. Further purification of the peptides was carried out by gel nitration on Sephadex G‐25 or by high‐voltage paper electrophoresis at pH 3.6 and 6.5. Nine peptides were obtained in pure form from fragment A and three peptides from fragment B, and their amino acid sequences were determined by the direct Edman method and by carboxy‐peptidase digestion technique. Overlapping peptides necessary for the alignment of the tryptic peptides from fragments A and B were obtained from a chymotryptic hydrolysate of fragment AB by gel filtration on Bio‐Gel P‐4, and their amino acid compositions and sequence analyses of some peptides made it possible to establish the amino acid sequence of an amino‐terminal region of the inhibitor consisting of 84 amino acid residues. The reactive site (Arg63‐Ile64) of the inhibitor to trypsin was involved in this region.