Bowman-Birk inhibitor, a major trypsin and chymotrypsin inhibitor from
soybean, has 71 amino acids with 7 disulfide bonds. Conformation of B
owman-Birk inhibitor in native state, after heating, and after disulfi
de bonds were broken by sodium metabisulfite was determined by circula
r dichroism. The native Bowman-Birk inhibitor has 61% beta-sheet, 38%
unordered form, 1% beta-turn, and no alpha-helical structure. There wa
s no significant change in conformation after Bowman-Birk inhibitor wa
s heated at 80 degrees C for 1 h in phosphate buffer. There was a decr
ease 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 metabisul
fite-phosphate buffer. Although the change in conformation after disul
fide bonds of Bowman-Birk inhibitor were broken was statistically sign
ificant (P < 0.05), the magnitude of the change was not large. The dat
a support Bowman-Birk inhibitor's having a stable conformation even af
ter disulfide bonds are broken.