Kinetics of the Reduction of Cystine and Re- Lated Dithio (r-s-s-r) Acids by Reversible Oxidation-reduction

The reduction of cystine and related dithio acids (R-S-S-R) to thiol acids (R-S-H) presents an interesting phase in the study of the oxidation and reduction properties of the cysteine-cystine and other dithio-thiol acid systems. Reaction rates of the reduction of these compounds by the reversible chromous-chromic and vanadous-vanadic systems, have been determined under various conditions of concentrations of reactants, acidity, temperature, and oxidation-reduction potentials of the reducing system. Information of particular biochemical interest has been obtained regarding the possible mechanism of the reduction of R-S-S-R to R-S-H, the nature of the apparent reversibility of the system, and the effect of the constitution of the attached groups on the ease of reduction of R-S-S-R to R-S-H. Also of interest is the effect of the oxidation-reduction potential of the reagent on the rate of the reduction. The “reduction” potentials of cysteine and other thiol compounds and their reaction towards various oxidizing agents have been extensively investigated in recent years but the “oxidation” potential and oxidizing properties of cystine and dithio acids (R-S-S-R) have received but little attention apparently for the reason that cystine and the other dithio compounds appeared to be relatively unreactive under the conditions studied. Dixon and Quastel (7), Michaelis and Flexner (13), and Kendall