The kinetics of DNA cleavage, especially the conversion of supercoiled to nicked DNA, by two 4,4'- dimethyl-2,2'-pyridyl(dmbpy) manganese(Ⅱ) complexes, Mn(dmbpy)2(OCN)2(1) and Mn(dmbpy)2(dca)2(2), was investigated. Results show that there is similar kinetic characterization for complex 1-mediated DNA cleavage and 2- mediated DNA cleavage. For the conversion of supercoiled to nicked DNA, the overall reaction is three orders, i.e., the reaction rate is proportional to CDNA substrate, Ccomplexes and CH2O2, respectively. The rate constants are(2.54±0.36)×104 and (2.51±0.45)×104 L2·mol-2·s-1 at 37℃ for 1 and 2-mediated DNA cleavage, respectively. The temperature dependence of the rate constants results in the comparable activation energies(Ea), activation enthalpies(△H≠) and activation entropies (△S≠) for 1 and 2-mediated reactions, which suggests that the two reactions have similar organized transition states. Based on the above results, a mechanism for the Mn (Ⅱ) complexes-mediated DNA cleavage was proposed.%对2个4,4'-二甲基-2,2'-联吡啶锰(Ⅱ)配合物在生理条件及H2O2的存在下对DNA切割的动力学进行了研究.结果表明,这2个配合物分别存在下的DNA切割反应具有相似的动力学反应特征.其中对超螺旋DNA切割成缺口DNA步骤,均表现为三级反应,即反应速率分别与底物DNA的浓度、配合物的浓度和H2O2的浓度的一次方成正比;同时得到了2个反应的速率常数、活化能(Ea)、活化焓(△H≠)和活化熵(△S≠)等动力学参数,并根据这些结果提出了一个可能的氧化切割反应机理.
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