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 y ields 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 hydr olysates by high pressure liquid chromatography (HPLC) and photodiode array UV spectroscopy. In the case of DNA several methylated adducts w ere identified, namely N-7-methylguanine, C-8-methylguanine, N-3-methy ladenine, and O-6-methylguanine. By contrast, 2'-deoxyguanosine is alk ylated almost exclusively to C-8-methyl-2'-deoxyguanosine. These resul ts constitute the first evidence that TBHP is able to alkylate DNA.