Dynamics of hapten-antibody interaction. Studies on a myeloma protein with anti-2,4-dinitrophenyl specificity.

Abstract The kinetics of interaction between IgA immunoglobulin produced by the mouse plasma cell tumor MOPC 315 and its ligands have been investigated by the temperature-jump-chemical relaxation method. This protein was previously shown to have homogeneous binding sites with affinity towards dinitrophenyl and trinitrophenyl derivatives, comparable to conventionally induced antibodies. The homogeneity of the protein 315 allows a precise analysis of antibody-hapten reaction dynamics, which hitherto were investigated on heterogeneous antibody populations. Three different preparations of the 315 protein were studied for their interaction with either ϵ, N -DNP † -lysine or DNP-glycine: (1) polydisperse form obtained from the serum; (2) monomeric form obtained on mild reduction and alkylation; (3) Fab′ fragment obtained after cleavage with pepsin. In all three cases only a single relaxation time was observed over a broad concentration range. From the dependence of the relaxation times on the free protein and ligand concentrations a single-step binding mechanism was deduced and the specific rates for binding and dissociation were calculated. For all three protein forms, very similar rate constants were observed, implying that there is no effect on the binding dynamics of the protein by either the Fc portion of the molecule or the state of aggregation.