In the DNA breakage, metal ions play important roles as cofactors for nucleases activity or as central metals in the chemical nuclease mimetics. In addition, some metal ions such as Fe2+
can induce oxidative DNA cleavage in the presence of oxidizing reagent via the Fenton reaction. In the almost cases, metal ions are believed to act as an electron donor or an acceptor to induce oxidative DNA cleavage. In this experiment, we have studied the pBR322 plasmid DNA cleavage action of Cu2+, Mn2+, Ni2+, Co2+, and Zn2+ ions. We found that Cu2+, Mn2+, Zn2+, and Co2+ can induce plasmid DNA cleavage but Ni2+ may not. In the gel electrophoresis experiment, Mn2+, Zn2+, and Co2+ produced two new plasmid forms with altered electrophoretic mobility, the circular relaxed and the linear forms. The formation of these new plasmid forms significantly depended on the concentration of metal ions. On the other hands, Cu2+ ion produced only the open circular form but not the linear form. In addition, the formation of the product was not seems to be dependent on the concentration of the Cu2+ ion adopted in this work. In the experiment using various radical scavengers, the DNA cleavage might be induced by the coupled effect of hydroxyl radical and singlet oxygen radical. Based on the above results, we will propose a mechanism of metal ions induced DNA cleavage reaction.