Flemmig Jörg, Arnhold Jürgen
Institute of Medical Physics and Biophysics, University of Leipzig, Leipzig, Germany.
Eur Biophys J. 2007 Apr;36(4-5):377-84. doi: 10.1007/s00249-006-0093-3. Epub 2006 Sep 20.
Ferrous ion-induced generation of single and multiple strand breaks in the DNA plasmid pBR322 induces the formation of two new plasmid forms with altered electrophoretic mobility. The yield of these plasmid forms, the circular relaxed and the linear forms, depended on the applied Fe(2+) concentration. This property was independent of the presence of hydrogen peroxide in the incubation mixture indicating the lack of Fenton chemistry to explain the DNA degradation. The removal of dioxygen or the presence of superoxide dismutase diminished partially the yield of ferrous ion-induced DNA plasmid degradation, while catalase was without any effect. Autoxidation of divalent iron as followed by the formation of a coloured iron-phenanthroline complex was enhanced in a concentration-dependent manner by phosphate and bicarbonate and very efficiently using a mixture of 0.15 M NaCl, 1.2 mM phosphate, 23.8 mM bicarbonate, pH 7.4, that concentrations correspond closely to the intracellular values of buffer components. Thus, the formation of a yet unknown reactive species from Fe(2+), and dioxygen, that is complexed to buffer components especially phosphate and its contribution in DNA plasmid degradation is more likely than the often cited formation of hydroxyl radicals in result of the Fenton reaction from Fe(2+) and hydrogen peroxide.
亚铁离子诱导DNA质粒pBR322产生单链和双链断裂，导致形成两种电泳迁移率改变的新质粒形式。这些质粒形式，即环状松弛型和线性型的产量，取决于所施加的Fe(2+)浓度。该特性与孵育混合物中过氧化氢的存在无关，这表明缺乏芬顿化学反应来解释DNA降解。去除二价氧或存在超氧化物歧化酶会部分降低亚铁离子诱导的DNA质粒降解产量，而过氧化氢酶则没有任何影响。磷酸盐和碳酸氢盐以浓度依赖的方式增强了二价铁的自氧化作用，随后形成了有色的铁-邻菲罗啉络合物，并且使用0.15 M NaCl、1.2 mM磷酸盐、23.8 mM碳酸氢盐、pH 7.4的混合物非常有效，该浓度与缓冲成分的细胞内值密切对应。因此，由Fe(2+)和二价氧形成一种未知的反应性物种，该物种与缓冲成分特别是磷酸盐络合，并且其在DNA质粒降解中的作用比通常认为的由Fe(2+)和过氧化氢通过芬顿反应形成羟基自由基的作用更有可能。
