Ultracentrifugal Studies of the Reaction of IgM Anti-γ-Globulin Subunits with Human IgG¹

Subunits were produced from three human IgM anti-γ-globulins by reduction with ethylmercaptan and alkylation with iodoacetamide. The formation of soluble complexes by reaction of the subunits with human IgG was investigated by quantitative sedimentation analysis. The subunits from each of the anti-γ-globulins formed a major complex component which sedimented at approximately 8 or 9 S. The sedimentation properties of the complex components were found to be independent of the amount of IgG reacted with the subunits. In the presence of an excess of active subunits, the quantity of complexes formed by the subunits from each of the anti-γ-globulins was twice the quantity of IgG present in the reaction mixture. Evidence was obtained that most, if not all, of the IgG in these reaction mixtures reacted with the subunits. In the presence of an excess of IgG, the quantity of complexes remained constant regardless of the amount of IgG used in the reaction mixtures. The results were discussed in terms of their possible significance with regard to the valence of the subunits.