The Far Ultraviolet Optical Rotatory Dispersion, Circular Dichroism, and Absorption Spectra of a Myeloma Immunoglobulin, Immunoglobulin G

Abstract

Abstract The optical rotatory properties of a myeloma globulin, immunoglobulin G (IgG), and a normal individual IgG in the far ultraviolet were investigated by rotatory dispersion, circular dichroism, and absorption spectroscopy. The optical rotatory dispersion of the myeloma immunoglobulin displayed two peaks, one at 205 mµ and the other at 210 mµ, and a trough at 228 mµ, a lesser one at 230 mµ, and a deeper one at 198 mµ. The normal individual γ-globulin displayed a peak at 208 mµ and a trough at 228 to 230 mµ. The rotatory dispersion in acid media was suggestive of the formation of right handed α helices in both immunoglobulins. Circular dichroic analysis of the myeloma IgG showed seven dichroic bands, at 202 mµ (+), 217 mµ (-), 225 mµ (-), 242 mµ (-), 265 mµ (+), 284 mµ (+), and the beginning of a negative band centered below 195 mµ (≃192.5 mµ). Application of the Kronig-Kramers transform gave an optical rotatory dispersion curve compatible with the one obtained experimentally. The peptide bond extinction, calculated from far ultraviolet absorption spectra, displayed a hypochromicity for both immunoglobulins. The far ultraviolet optical rotatory dispersion analyses of the myeloma IgG cleaved by oxidative sulfitolysis showed the disulfide bonds joining the heavy and light chains to be essential for the maintenance of certain electronic transitions present in the native protein. The major transitions, however, appeared to be unaffected by this treatment. Comparison of the Cotton effects of the sulfitolyzed product in acid with those of the whole molecule in acid (pH 2.4) showed that these S—S bonds are important in restricting conformation change in the presence of this denaturing agent.