Association-dissociation behavior of sesame alpha-globulin in electrolyte solutions

The major protein fraction, alpha-globulin, of sesame seed (Sesamum indicum L.) contains subunits which are associated predominantly by hydrophobic interactions. Effects of various salts show the following effectiveness of anions in dissociating the proteins, SO4(2-) less than Cl- less than Br- less than ClO4- less than SCN- less than or equal to I- less than CCl3COO-, the first two members being association-inducing ions. CCl3COONa is found to be the most effective among the series in causing dissociation. The cations Li+, Na+, K+, and Cs+ induce association, the order of effectiveness being Cs+ approximately K+ greater than or equal to Na+ greater than Li+. The low concentration of salts (anions) necessary to induce dissociation does not involve a detectable change in protein conformation. The discrepancy between the effectiveness of the anions in dissociating the protein and the Hofmeister pattern of these ions has been discussed.