Kinetics of binding reactions of an antibody molecule with haptens on a membrane surface

Direct measurement has been made of the reaction rate of binding of a bivalent antibody and fluorescent haptens, which were covalently bound on a model membrane surface, by a method of stopped-flow fluorometry. The result was interpreted as indicating that the reaction takes place in two steps: (i) binding of a hapten with one of the two antigen-combining sites of an antibody molecule, and (ii) binding of another hapten with the other site of the antibody molecule in question. The rate of the second step was found to depend on the fluidity of the membrane.