Role of disulfide bonds upon the structural stability of an amaranth globulin

Analysis of globulin-P, the polymerized amaranth globulin, gave a low amoun t of free sulfhydryls (10.2 +/- 0.5 mu mol/g) from which 7 +/- 1 mu mol/g w as buried inside the molecule. In addition, its disulfide content was high (51 +/- 1 mu mol/g) and similar to soybean 11S globulin content. The more e xposed disulfide bridges were found to be stabilizing polymers, whereas the less reactive bridges were either linking P-20 and P-30 polypeptides or fo rming intrachain linkages. It was found that the buried bonds participate i n the stabilization of folded polypeptides and the quaternary structure of the globulin. In turn, the dissociation of polymers and disruption of the q uaternary structure by the action of 2-mercaptoethanol reverted upon remova l of the reducing agent. This demonstrates that the polymerized state and t he quaternary structure of the molecules are most favorable from the thermo dynamic point of view. The similar content of SH and SS in globulin-P and g lobulin-S found in this laboratory suggests that the differences between th ese proteins may be ascribed to other compositional differences.