Studies of Ligand Binding to Cholera Toxin, III

Abstract
Binding parameters for the interaction of cholera toxin and choleragenoid with monosialo-gangliotetraose, the oligosaccharide moiety of ganglioside II3NeuAc-GgOse4-Cer, were measured by equilibrium displacement dialysis. The experimental data were evaluated by a curve fitting computer program. The binding curves obtained to 6.degree. C reflected positive cooperativity with average Hill coefficients in the range of 1.16-1.25. The cholera toxin and its ganglioside-binding protomer B-protein bind 4 mol of monosialo-gangliotetraitol/mol of protein. The presence of disulfide-cleaving agents like 2-mercaptoethanol did not eliminate the cooperativity of the binding characteristics, but increased the Hill coefficient.