Studies on Soybean Trypsin Inhibitors

Abstract

For the elucidation of the amino‐acid sequence of the carboxyl‐terminal region of soybean trypsin inhibitor (Kunitz), fragments C and D were digested with trypsin, and the resulting peptides were separated by ion‐exchange chromatography on Dowex 50X2 or by gel nitration on Bio‐Gel P‐4.Further fractionation and purification of the peptides were performed by ion‐exchange chromatography on Dowex 1X2, by gel filtration on Bio‐Gel P‐2 or by high‐voltage paper electrophoresis at pH 1.9 and 3.6.Three peptides were obtained in pure form from fragment C and ten peptides from fragment D, 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 fragment D were obtained from a chymotryptic hydrolysate of fragment D.Nine main peptides and nine minor peptides were obtained. The amino acid composition and the partial amino‐acid sequence of the 18 chymotryptic peptides of fragment D made it possible to establish the amino‐acid sequence of the carboxyl‐terminal region of the inhibitor.The complete amino‐acid sequence of soybean trypsin inhibitor (Kunitz) deduced here was compared with that of Bowman‐Birk inhibitor, another well‐known soybean proteinase inhibitor.