Changes of the Conformation of Rabbit IgG Antibody Caused by the Specific Binding of a Hapten

The conformation of rabbit antibody specific for the ρ‐azophenyl‐β‐lactoside group was studied by small‐angle X‐ray scattering and the effect of interaction with hapten evaluated. The binding of hapten to the antibody caused a change in the conformation of the protein. The experimental findings indicate that the radius of gyration and the volume of the antibody become smaller by 2 to 3% as a result of interaction with hapten when 50% of the combining sites are occupied. Since the typical shape of the scattering curves remains the same it is inferred that the change of conformation consists mainly of a volume contraction whereas the overall shape, which is best described by T‐shaped models, is not essentially modified.