Characterization of the cleavage products of human serum immunoglobulin disulphide bonds. I. S-Sulpho derivatives

Abstract

An examination of variables, including amount of catalyst, pH, sulphite concentration, specific buffer salts, and time of reaction led to conditions for the quantitative sulphitolysis of human serum immunoglobulin disulphide bonds. The cleavage was carried out in the absence of dispersing agents, using air as oxidant and cupric ions as catalyst. The treated protein was characterized by solubility, exclusion chromatography, ultracentrifugation, and immunoelectrophoresis. Separation into three fractions of different molecular weight was achieved by passage through Sephadex G-200 gel. Efforts to eliminate the proportion of aggregated material, which showed no tendency to establish an equilibrium with the remaining two unaggregated fractions, were largely unsuccessful. It was concluded that non-covalent forces play a significant role in antibody interactions. The isolated fractions were individually characterized by sedimentation, heat precipitation, immunoelectrophoresis, and quantitative analysis of amino-terminal residues. This led to the demonstration of at least two polypeptide chains present in each fraction.