Quantitative analysis of the interaction between lysozyme and monoclonal antibody D1.3

The method of sedimentation equilibrium has been used to determine the stoichiometry and binding constant for the interaction between hen egg white lysozyme and monoclonal antibody D1.3. The procedures described allow the relative binding affinities of 125I-labelled lysozyme and unlabelled lysozyme to be compared. The data indicate that labelled and unlabelled lysozyme bind to monoclonal D1.3 with similar affinity (binding constant, K = 1.6 x 10(9)/M). Using solid-phase methods estimates obtained for the binding constant were lower and dependent both on the amount of antigen coated on the plate and the dilution of primary antibody (D1.3). These data were not consistent with a simple equilibrium binding model, suggesting kinetic or orientation effects. In contrast sedimentation equilibrium experiments provide a rapid and accurate method for determining both the stoichiometry and binding constants for the interaction between antigens and antibodies.