Aggregation of an immunoglobulin fragment by sulfhydryl oxidation

Abstract

An immunoglobulin of the IgG family has been isolated from the serum of a patient with multiple myeloma. The IgG was subjected to plasmin digestion and the resulting Fab fragment was isolated and characterized. Incubation of this fragment in denaturing solvents, such as aqueous 8 M urea at either pH 3.4 or pH 8.2, resulted in the formation of a dimer as the main product. In some cases more complex products were formed in addition to the dimer. Free sulfhydryl titrations and blocking experiments indicated that the transformation reaction consisted of cross-linking of two Fab fragments by oxidation of sulfhydryl groups. The original immunoglobulin proved to have two sulfhydryl groups per mole, which are unreactive except in the presence of denaturing solvents.