The Role of the Intrachain Disulfide Bond in the Conformation and Stability of the Constant Fragment of the Immunoglobulin Light Chain1

Abstract

The conformation and stabilities of the C_L fragment isolated from a type λ Bence Jones protein and the fragment in which the intrachain disulfide bond had been reduced were studied by measuring CD₁ fluorescence, and ultraviolet absorption. The results indicated that no great conformational change occurs on reduction of the disulfide, unless the SH groups are alkylated. Intact C_L was more resistant than reduced C_L to guanidine hydrochloride. The denaturation curves were analyzed using an equation based on the binding of guanidine hydrochloride and the free energy changes of denaturation in the absence of the denaturant were estimated as about 6kcal-mol^-1 for intact C_L and about 1.8 kcal-mol^-1 for reduced C_L. The difference in stability between intact C_L and reduced C_L was explained to a great extent in terms of the entropy change associated with reduction of the intrachain disulfide bond of the fragment in the denatured state.