Dissociation of Waldenström's immunoglobulin M by the disulfide interchange reaction

Abstract

Immunoglobulin M proteins isolated from patients with Waldenström's macroglobulinemia were rapidly dissociated into subunits by an interchange reaction with diethanoldisulfide or cystamine. Three hours incubation at room temperature in pH 8·5 buffer with the disulfide compound (0·1 M) and mercaptoethanol (0·005 M) provided suitable conditions for complete dissociation. Incomplete dissociation resulted when the concentration of mercaptoethanol in the reaction mixture was less than 0·004 M or more than 0·02 M. No dissociation was evident when the mercaptoethanol was omitted from the reaction mixture. Use of buffers having pH valves of less than 8·0 resulted in a decrease in the yield of subunits. The extent of dissociation was less when the disulfide compound was omitted from the reaction mixture than when it was present. The subunits were stable, did not possess free sulfhydryl groups, and closely resembled those produced from the same IgM proteins by reduction and alkylation with respect to molecular weight. Although cleavage of the intersubunit disulfide bonds was essentially complete, only partial cleavage of the interchain disulfide bonds occurred under the conditions used in the present study.