Reassociation of IgM Subunits in the Presence and Absence of J Chain

IgM subunits and J chains from a Waldenström macroglobulin reduced with 20 mM dithiothreitol were separated by gel filtration. One half of the subunits was reoxidized in the absence, the other half in the presence of J chains. Ultracentrifugal analysis revealed that 1. Reassociation of IgM subunits to larger products occurred in the absence and in the presence of J chains. 2. In the presence of J chains mainly pentamers were formed while subunits without J chains assembled to larger molecules. The results suggest that J chains have a controlling function on the assembly of IgM subunits and prevent the assembly of more than 5 subunits per IgM molecule.