DNA methylation by tert-butyl hydroperoxide-iron (II)

Reduction of tert-butyl hydroperoxide (TBHP) by iron (II) at pH 4.0 or pH 7.0 in the presence of calf thymus DNA led to generation of high yields of methyl radicals and to DNA methylation. Methyl radicals were identified by spin-trapping experiments with 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN). The methylated DNA-base adducts were identified in treated DNA hydrolysates by high pressure liquid chromatography (HPLC) and photodiode array UV spectroscopy. In the case of DNA several methylated adducts were identified, namely N7-methylguanine, C8-methylguanine, N3-methyladenine, and O6-methylguanine. By contrast, 2'-deoxyguanosine is alkylated almost exclusively to C8-methyl-2'-deoxyguanosine. These results constitute the first evidence that TBHP is able to alkylate DNA.