Reduction of the buried intrachain disulfide bond of the constant fragment of the immunoglobulin light chain: global unfolding under physiological conditions

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Abstract
The constant (CL) fragment of the immunoglobulin light chain contains only one intrachain disulfide bond buried in the interior of the molecule. The kinetics of reduction with dithiothreitol of the disulfide bond were studied at various concentrations of guanidine hydrochloride at pH 8.0 and 25.degree. C. It was found that the disulfide bond is reduced even in the absence of guanidine hydrochloride. The results of the reduction kinetics were compared with those of the unfolding and refolding kinetics on the CL fragment previously reported [Goto, Y., and Hamaguchi, K. (1982) J. Mol. Biol. 156, 891-910]. It was shown that the reduction of the disulfide bond proceeds through a species with a conformation very similar to that of the fully unfolded one and that the CL fragment undergoes global unfolding transition even in water.