METHYLPEROXYL RADICALS AS INTERMEDIATES IN THE DAMAGE TO DNA IRRADIATED IN AQUEOUS DIMETHYL-SULFOXIDE WITH GAMMA-RAYS

Using agarose gel electrophoresis, we have measured the yields of DNA single-strand breaks (SSBs) for plasmid DNA gamma-irradiated in aerobi c aqueous solution, Incubation after irradiation with the base damage repair endonucleases formamidopyrimidine-DNA N-glycosylase (FPG) or en donuclease III (endo III) results in an increase in the yield of SSBs. In the absence of dimethyl sulfoxide (DX;ISO) during irradiation, thi s increase is consistent with the yields of known substrates for FPG a nd endo III as determined by gas chromatography/mass spectrometry. Aft er irradiation in the presence of 1 mol dm(-3) DMSO, the increase in t he yield of SSBs after enzyme incubation was further enhanced by a fac tor of about 5 to 7. The magnitude of this effect, the inability of ac rylamide or oxygen to suppress it, and its attenuation by N,N,N',N'-te tramethylphenylenediamine (TMPD) or glycerol all suggest that the meth ylperoxyl radical (derived from DMSO) is involved as an intermediate, Reactions of the methylperoxyl radical(or some other species derived f rom it) do not result in strand break damage, but are responsible for DNA base damages which are recognized by FPG and endo III. (C) 1996 by Radiation Research Society