Dissociation, Reaggregation, and Subunit Structure Studies of Some Human γM-Globulins

Abstract

Abstract Reduction of γM-globulins with various mercaptans produces 8 S subunits. Upon removal of the mercaptan, variable degrees of reaggregation of these subunits take place, depending on the particular γM-globulin and the dissociating mercaptan reagent used. The presence of imidazole or methionine inhibits the extent of reaggregation. The 8 S subunit remaining after removal of the mercaptan appears to be a mixed disulfide of the protein and has a molecular weight near 200,000. It persists in this form at pH 4 and in 6 m guanidine. Extensive alkylation of reduced protein gives a subunit which readily loses light (L) chain components. The molecular weight of this reduced-alkylated protein is near 160,000. It is partially dissociated into heavy (H) and L chains at pH 4 and completely so in 6 m guanidine. L chain protein formed at pH 4 in the absence of guanidine may be readily crystallized. The L and H chains have molecular weights near 22,500 and 66,000, respectively, in 6 m guanidine. Molecular weight data indicate that a 1,000,000 mol wt γM-globulin is composed of five subunits of mol wt 200,000. These subunits appear to consist of three L chains and two H chains, and the purified reduced-alkylated subunit, of one L chain and two H chains.