One-electron oxidation of plasmid DNA by selenium(V) species

Purpose : To employ the γ-radiation-generated selenium(V) one-electron-oxidizing agent SeO 3 •- for the preparation of guanyl radicals in plasmid DNA, and to compare the behaviour of this reagent with that of other similarly reactive oxidant species. Materials and methods : Plasmid DNA in aerobic aqueous solution was irradiated with 137 Cs γ-rays (662 keV). The solutions also contained up to 4 ×10 -2 mol dm -3 sodium selenate (Na 2 SeO 4) and/or up to 10 -1 mol dm -3 sodium biselenite (NaHSeO 3) , as well as auxiliary scavengers such as DMSO or glycerol. In some cases, reducing agents such as ferrocyanide were also present. After irradiation, the plasmid was incubated with the Escherichia coli base excision-repair endonuclease formamidopyrimidine-DNA N -glycosylase (FPG). These treatments produced strand breaks in the plasmid. The yields of these strand breaks were quantified by agarose gel electrophoresis. Results : In general, γ-irradiation produced single-strand breaks (SSB) in plasmid DNA. Subsequent ...