Li A Z, Huang H, Re X, Qi L J, Marx K A
Department of Chemistry, University of Massachusetts, Lowell 01854, USA.
Biophys J. 1998 Feb;74(2 Pt 1):964-73. doi: 10.1016/S0006-3495(98)74019-6.
The behavior of alkaline earth metal cations (Mg2+ and Ca2+) and transition metal cations (Zn2+ and Cu2+) interacting with lambda-DNA-HindIII fragments ranging from 2,027 to 23,130 bp in Tris-borate-EDTA buffer solutions was investigated. The divalent counterions competed with Tris+ and Na+ for binding to polyion DNA, and the competition binding situations were investigated by measuring the reduction of the DNA mobility, by pulsed- or constant-field gel electrophoresis. The interaction of Mg2+ with DNA was intensively studied over a wide range of Mg2+ concentrations. In addition, we examined the competition binding as a function of ionic strength and DNA size. To compare valence effects, we studied Co(NH3)6(3+) interaction with DNA fragments under conditions similar to that of Mg2+. At relatively low Mg2+ concentration, the normalized titration curves of DNA mobility were well fit by Manning's two-variable counterion condensation (CC) theory. The agreement between the predicted value (total charge neutralization fraction theta) from Manning's CC theory and the data based on our measured DNA electrophoretic mobility reduction was consistent under our experimental conditions. In contrast to alkaline earth metal cations (Mg2+ and Ca2+), different binding behaviors were observed for the transition metal cations (Zn2+ and Cu2+). These differences highlight the usefulness of our reduced DNA electrophoretic mobility measurement approach to describing cation interactions with polyelectrolyte DNA.
研究了碱土金属阳离子（Mg2+和Ca2+）以及过渡金属阳离子（Zn2+和Cu2+）在Tris-硼酸-EDTA缓冲溶液中与长度范围为2027至23130 bp的λ-DNA-HindIII片段的相互作用。二价抗衡离子与Tris+和Na+竞争结合聚离子DNA，并通过脉冲或恒场凝胶电泳测量DNA迁移率的降低来研究竞争结合情况。在较宽的Mg2+浓度范围内深入研究了Mg2+与DNA的相互作用。此外，我们还研究了竞争结合与离子强度和DNA大小的关系。为了比较价态效应，我们在与Mg2+相似的条件下研究了Co(NH3)6(3+)与DNA片段的相互作用。在相对较低的Mg2+浓度下，DNA迁移率的归一化滴定曲线与曼宁的双变量抗衡离子凝聚（CC）理论拟合良好。在我们的实验条件下，曼宁CC理论预测值（总电荷中和分数θ）与基于我们测量的DNA电泳迁移率降低数据之间的一致性良好。与碱土金属阳离子（Mg2+和Ca2+）不同，过渡金属阳离子（Zn2+和Cu2+）表现出不同的结合行为。这些差异突出了我们降低DNA电泳迁移率测量方法在描述阳离子与聚电解质DNA相互作用方面的实用性。
