Inhibition of DNA-ethidium bromide intercalation due to free radical attack upon DNA

The fluorescent intercalation complex of ethidium bromide (ETB) with DNA was used as a probe to compare the effects of various radicals with respect to impairment of the DNA base-pair region.^⋅OH radicals inhibit up to 0.7 dye intercalations per^⋅OH at low salt concentration, and for various oxidizing species the effect decreases in the order^⋅OH > Br ₂ ^{⋅ −} > N ₃ ^⋅ $ > > $ (SCN) ₂ ^{⋅ −}. DNA impairment by the^⋅OH product of Met-Gly is comparable to that of N ₃ ^⋅ , but no effect was found due to the interaction between DNA and Lys-Tyr-Lys phenoxyl radicals. The reducing speciese _aq ⁻ , H^⋅, O ₂ ^{⋅ −}, and CO ₂ ^{⋅ −} hardly affect the DNA-ETB intercalation.