Beckman R A, Mildvan A S, Loeb L A
Biochemistry. 1985 Oct 8;24(21):5810-7. doi: 10.1021/bi00342a019.
Manganese is mutagenic in vivo and in vitro in studies with a variety of enzymes and templates. Using Escherichia coli DNA polymerase I with poly[d(A-T)] and phi X174 DNA templates, we analyzed the mechanism of manganese mutagenesis by determining the dependence of error rate on free Mn2+ concentration and comparing this to measured dissociation constants of Mn2+ from enzyme, template, and deoxynucleoside triphosphate substrates. This comparison suggests several conclusions: (1) At very low Mn2+ concentrations, the enzyme is activated at high fidelity. Thus, it is unlikely that activation with manganese per se significantly alters the conformation of the enzyme so as to affect nucleotide selection. (2) At low free Mn2+ concentrations (less than 100 microM), manganese causes errors in incorporation via its interaction with the DNA template. The concentration dependence of mutagenesis is determined by the strength of binding Mn2+ to the particular DNA template used. The data do not allow one to rule out the possibility that Mn2+-deoxynucleoside triphosphate interactions contribute to mutagenesis in selected situations. This range of free Mn2+ concentrations is the one of greatest relevance for in vivo mutagenesis. (3) At higher concentrations (between 500 microM and 1.5 mM), further mutagenesis by Mn2+ occurs. This mutagenesis probably is due either to binding of manganese to single-stranded regions within the DNA or to weak accessory sites on the enzyme.
在针对多种酶和模板的体内和体外研究中，锰具有致突变性。我们使用大肠杆菌DNA聚合酶I以及聚[d(A-T)]和φX174 DNA模板，通过测定错误率对游离Mn2+浓度的依赖性，并将其与从酶、模板和脱氧核苷三磷酸底物测得的Mn2+解离常数进行比较，分析了锰致突变的机制。这种比较得出了几个结论：(1) 在极低的Mn2+浓度下，酶以高保真度被激活。因此，锰本身的激活不太可能显著改变酶的构象从而影响核苷酸选择。(2) 在低游离Mn2+浓度（小于100微摩尔）下，锰通过与DNA模板的相互作用导致掺入错误。诱变的浓度依赖性由Mn2+与所用特定DNA模板的结合强度决定。这些数据无法排除在特定情况下Mn2+ - 脱氧核苷三磷酸相互作用导致诱变的可能性。这个游离Mn2+浓度范围与体内诱变最为相关。(3) 在较高浓度（500微摩尔至1.5毫摩尔之间）下，Mn2+会进一步诱变。这种诱变可能是由于锰与DNA内的单链区域结合，或者是由于酶上的弱辅助位点。
