DNA breakage by tannic acid and Cu(II): sequence specificity of the reaction and involvement of active oxygen species.

Tannic acid has numerous chemical, food and pharmacological applications. In the presence of Cu(II) and molecular oxygen it was found to cause breakage of calf thymus DNA and supercoiled plasmid DNA. Treatment of lambda phage DNA with tannic acid protected cleavage with restriction endonucleases DraI and EcoRI* but not with SmaI and HaeIII. The results indicate that under the conditions used tannic acid preferably binds to AT base pairs. Restriction analysis of open circular form II plasmid DNA generated by tannic acid-Cu(II) treatment further showed that the strand breakage is caused at specific sites or sequences. In this reaction Cu(I) was shown to be an essential intermediate by using the Cu(I) sequestering reagents neocuproine and bathocuproine. By using job plots, we established that in the absence of DNA, six Cu(II) ions can be reduced by one tannic acid molecule. The involvement of active oxygen species in the reaction was established by the inhibition of DNA breakage by superoxide dismutase, thiourea, mannitol, formate and catalase.