The reaction of sulfite radical anion with nucleic acid components.

The sulfite radical anion (SO3.-) is the first intermediate in the autoxidation of sulfite to sulfate. Using competition kinetics, its reactivities with the nucleic acid bases and the corresponding nucleosides were investigated. The second order rate constants were found to be rather low, k less than or equal to 1 x 10(6) dm3mol-1s-1 at pH 7. As a competitor, the carotenoid crocin was used, which was found to be bleached very efficiently by SO3.- (k = 1.0 x 10(9) dm3mol-1 s-1).