A Specific and Sensitive Assay for Disulfides

A specific and sensitive assay for disulfide groups has been developed, based on reduction with dithioerythritol or dithiothreitol and determination of the resulting monothiols with 5,5′-dithiobis(2-nitrobenzoic acid) in the presence of arsenite. The dissociation constants for the complexes formed between arsenite and dithioerythritol, dithiothreitol, 1,3-dithioglycerol, and 1,2-dithioglycerol have been measured, as well as the rate constants for the formation and breakdown of the complexes and for the bimolecular reaction between the complexes and 5,5′-dithiobis(2-nitrobenzoic acid). The pK values of dithiothreitol are 8.3 and 9.5, and those for dithioerythritol are 9.0 and 9.9.