SPONTANEOUS CLEAVAGE OF 4'-DNA RADICALS UNDER AEROBIC CONDITIONS : APPARENT DISCREPANCY BETWEEN TRAPPING RATES AND CLEAVAGE PRODUCTS

The O2-induced strand scission of 4‘-DNA radicals is initiated by a reversible O2 addition reaction. The rate coefficient of the O2 release from the single-stranded 4‘-DNA peroxyl radical is 1.0 s-1 at 20 °C. Because of this reversibility, an O2-dependent strand cleavage occurs only in the presence of H-donors that trap the 4‘-DNA peroxyl radicals, yielding DNA hydroperoxides. At very low H-donor concentrations the strand scission is the result of an O2-independent, spontaneous reaction even under aerobic conditions. Nevertheless, oxidative products can be formed from the fragments of this spontaneous DNA cleavage.