Characterization of Subunits from a Reconstituted Monoclonal Igm That Binds IgG

Abstract

The active products obtained by reassociation of the component polypeptide chains of a Waldenström's IgM that binds IgG were dissociated by reduction with mercaptoethanol and alkylation with iodoacetamide. Comparison of the resulting subunits to those obtained from the original IgM by physicochemical and immunochemical methods failed to reveal significant differences. The subunits from both sources demonstrated sd`_20,w values of 6.4S and appeared identical by Immunoelectrophoresis using antisera specific for IgM and κ type Bence Jones proteins. The quantity of light chains recovered by gel chromatography in 1 N acetic acid from the sub-units of the reconstituted IgM was comparable to that from the original IgM. In addition, the presence of active binding sites on the subunits from both the reconstituted and native IgM was indicated by ultracentrifugal studies that demonstrated the presence of soluble complexes after the addition of human IgG. The results indicate that the regeneration of active products from the μ and κ chains of this IgM was associated with the formation of a structural unit that shared many properties with the 7S subunit of the native molecule.