The Reaction of Superoxide Radical Anion with Dithiothreitol: A Chain Process

Article abstract of DOI:10.1021/j100165a024

The radical-induced oxidation of dithiothreitiol (DTT) by O2 to 4,5-dihydroxy-1,2-dithiane (ox-DTT) in aqueous solutions of pH 8.7 proceeds via a chain reaction.Radicals such as OH generated by the radiolysis of N2O/O2-saturated aqueous solutions abstract an H atom from DTT.The resulting DTT(-H)^. radicals cyclize and deprotonate, yielding the disulfide radical anion ox-DTT^.-.The latter reacts with O2 (k = 7.1 x 10⁸ dm³ mol^-1 s^-1) giving rise to ox-DTT and O2^.-.The G value of ox-DTT formation increases with decreasing dose rate, displaying a linear yield vs (dose rate)^1/2 relationship indicative of a chain reaction.The chain is inhibited by superoxide dismutase, showing that 02^.- is a chain carrier.Hydrogen peroxide is not a chain product, from which it is concluded that O2^.- does not abstract hydrogen from DTT but rather forms a short lived complex with the DTT anion which then predominantly decomposes into an RSO^. radical and an OH^- ion, (and to a lesser extent into an OH radical and an RSO^- ion).In a second step, the RSO^. radical reacts with DTT (probably the anionic form DTT^-), thus regenerating DTT(-H)^..The resulting sulfenic acid eliminates water and yields the chain product ox-DTT.An overall propagation rate constant of 35 dm³ mol^-1 s^-1 has been estimated.