Reaction of guanyl radicals in plasmid DNA with biological reductants : chemical repair of DNA damage produced by the direct effect of ionizing radiation

Purpose : It has been previously argued that the use of the one-electron oxidants (SCN) 2 •- and Br 2 •- with plasmid DNA leads to the formation of DNA guanyl radicals. These guanyl radical species are intermediates in the DNA damage produced by processes such as photo-ionization and ionizing irradiation. The present paper evaluates the use of thallium(II) ions (Tl II OH +) as the one-electron oxidant, and also determines rate constants for the reduction (repair) of guanyl radicals in plasmid DNA by a variety of reducing agents including the biologically important compounds ascorbate and glutathione. Materials and methods : Aqueous solutions of plasmid DNA containing 10 -3 mol dm -3 thiocyanate or thallous ions and a reducing agent (azide, nitrite, ferrocyanide, hexachloroiridate(III), iodide, ascorbate, glutathione, glutathione disulphide, methionine, tyrosine, 5-hydroxyindole-3-acetic acid, 10 -7 -10 -4 mol dm -3) were irradiated with 137 Cs γ-rays (662 keV). After irradiation, the plasmid was incubated...