Flexible structure of immunoglobulin G molecule. Fluorescence depolarization studies on hapten-antihapten antibody...

Fluorescence depolarization studies on immunoglobulin G, Fab'2 and Fab' fragments were carried out using isomeric anilinonaphthalenesulfonates and their corresponding rabbit antibody systems, and the values of the relaxation time rho(h) were calculated. From the results it was confirmed that the IgG and Fab'2 fragment have a certain degree of segmental flexibility, and suggested that these divalent antibody molecules have the same order of flexibilities. Furthermore, the rhoh values of the Fab' fragments from each antibody preparation were also determined and conflicting results were obtained with the samples from two different kinds of antibody systems against the isomeric ligands. The results were discussed with special references to the orientation of ligands bound to the antibody combining sites.