Studies on soybean trypsin inhibitors. IV. Complete amino acid sequence and the anti-proteinase sites of Bowman-Birk soybean proteinase inhibitor.

Abstract

Bowman-Birk inhibitor was partially hydrolyzed with chymotrypsin [EC 3. 4. 4. 5] at pH 3.0, and the subsequent reduction, S-carboxymethylation and gel filtration of the product yielded two fragments. One fragment containing a methionine residue was further degraded into two fragments with cyanogen bromide. By the amino acid determination and the terminal sequence analysis of these three fragments as well as of the whole protein, the tryptic peptides were aligned into the complete amino acid sequence of the inhibitor. The anti-chymotrypsin and the anti-trypsin sites of the inhibitor were also identified by the limited hydrolysis with these proteinases. The sequence of this inhibitor was found to be very similar to that of lima bean inhibitor IV (Tan and Stevens, 1971), and consisted of two homologous peptide regions, one includes the inhibitory site for trypsin [EC 3. 4. 4. 4] and the other that for chymotrypsin. Comparison with other leguminosae inhibitors was also discussed.