Abstract
The interaction between soybean 7S globulin and the carboxyl groups of cation-exchange resins of the carboxylate type was analyzed by using a surface plasmon resonance (SPR) technology with relevance to deamidation of the globulin. This interaction and the degree of deamidation were measured under conditions of buffered solutions of different salt, sodium ion concentration, and pH. Soybean 7S globulin was dissolved in various solutions and mixed with cation-exchange resins of the carboxylate type. After removal of the resins, the degree of deamidation of the soybean 7S globulin was measured. The affinity of soybean 7S globulin dissolved in various solutions for the carboxyl group was analyzed with a SPR biosensor (Biacore) by using a chip with carboxylates on a dextran matrix. The deamidation level of soybean 7S globulin and the affinity of soybean 7S globulin for the polymer-supported carboxylates were well correlated. Both of them became higher at lower sodium concentrations and were highest at pH 6.0. Among the buffers examined, the phosphate buffer was the most effective for deamidation of soybean 7S globulin; and the affinity of soybean 7S globulin in this buffer for the carboxylate groups on the SPR chips was the highest in the phosphate buffer. Therefore, deamidation of 7S globulin protein would effectively occur when the amide groups of glutamine and asparagine residues of the protein interact with the carboxylates on resins.
