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A combination of absorbance, fluorescence, and pre-steady-state methods are employed to study the binding kinetics of arsenicals to unfolded proteins with stoichiometries of 1 As(III) per 2 thiols for mono-methylarsenous (MMA) and aryl arsenical (PSAO) and 1 As(III) for every 3 thiols with arsenite. The results suggested that the ability of As(III) species to bind to unfolded cysteine-containing proteins might contribute to oxidative and protein folding stresses that are prominent features of the cellular response to arsenic exposure.

Mono-, di, and trimethyl ester analogues of tris(2-carboxyethyl)phosphine were synthesized to evaluate the role of carboxylate anions in the reduction mechanism, and to expand the range of phosphine reductants. Model disulfides, including a fluorescent disulfide-containing peptide (H3N(super +)-VTWCGACKM-NH2), and with protein disulfide bonds in thioredoxin and sulfhydryl oxidase, are used to determine the effectiveness of all four phosphines relative to the dithiothreitol.