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 applicatio ns. In the presence of Cu(II) and molecular oxygen it was found to cau se breakage of calf thymus DNA and supercoiled plasmid DNA. Treatment of lambda phage DNA with tannic acid protected cleavage with restricti on endonucleases DraI and EcoRI but not with SmaI and HaeIII. The res ults indicate that under the conditions used tannic acid preferably bi nds to AT base pairs. Restriction analysis of open circular form II pl asmid DNA generated by tannic acid-Cu(II) treatment further showed tha t the strand breakage is caused at specific sites or sequences. In thi s reaction Cu(I) was shown to be an essential intermediate by using th e Cu(I) sequestering reagents neocuproine and bathocuproine. By using job plots, we established that in the absence of DNA, six Cu(lI) ions can be reduced by one tannic acid molecule. The involvement of active oxygen species in the reaction was established by the inhibition of DN A breakage by superoxide dismutase, thiourea, mannitol, formate and ca talase.