Site-specific DNA damage induced by sulfite in the presence of cobalt(II) ion: Role of sulfate radical

Abstract

The reactivities of sulfite (SO 3 2−) with DNA in the presence of metal ions were investigated by a DNA sequencing technique using 32P-labeled DNA fragments obtained from human c-Ha- ras-1 protooncogene. Sulfite caused DNA damage in the presence of Co 2+, Cu 2+ and Mn 2+, although sulfite alone or metal ion alone did not. The order of inducing effect on sulfite-dependent DNA damage (Co 2+ > Cu 2+ > Mn 2+ > Fe 3+) was consistent with that of accelerating effect on the initial oxygen consumption rate of sulfite autoxidation. The DNA damage induced by sulfite plus Co 2+ was inhibited by 3,5-dibromo-4-nitrobenzenesulfonate, primary and secondary alchols, whereas it was not inhibited by SOD, catalase and tert-butyl alcohol. Incubation of DNA with sulfite plus Co 2+ followed by the piperidine treatment led to the predominant cleavage at the positions of guanine especially located 5' to guanine. Sulfite plus Cu 2+ gave a DNA cleavage pattern different from that induced by sulfite plus Co 2+. The photolysis of peroxydisulfate (S 8O 2 2−), which is known to produce SO 4 − radicals, gave a DNA cleavage pattern similar to that induced by sulfite plus Co 2+. ESR studies using spin-trapping reagent revealed the production of spin adduct possibly of SO 3 − radical in a solution of sulfite plus Cu 2+, whereas much less spin adduct was produced by sulfite plus Co 2+. The results suggest that sulfite is rapidly autoxidized in the presence of Co 2+ to produce SO 4 − radical causing site-specific DNA damage.