CONFORMATION OF BOWMAN-BIRK INHIBITOR

Bowman-Birk inhibitor, a major trypsin and chymotrypsin inhibitor from soybean, has 71 amino acids with 7 disulfide bonds. Conformation of Bowman-Birk inhibitor in native state, after heating, and after disulfide bonds were broken by sodium metabisulfite was determined by circular dichroism. The native Bowman-Birk inhibitor has 61% beta-sheet, 38% unordered form, 1% beta-turn, and no alpha-helical structure. There was no significant change in conformation after Bowman-Birk inhibitor was heated at 80 degrees C for 1 h in phosphate buffer. There was a decrease in beta-sheet and an increase in beta-turn structure after Bowman-Birk inhibitor was heated at 80 degrees C for 1 h in sodium metabisulfite-phosphate buffer. Although the change in conformation after disulfide bonds of Bowman-Birk inhibitor were broken was statistically significant (P < 0.05), the magnitude of the change was not large. The data support Bowman-Birk inhibitor's having a stable conformation even after disulfide bonds are broken.