Coffey R L, Trowbridge C G
Department of Chemistry, Emory University, Atlanta, Georgia 30322.
Arch Biochem Biophys. 1990 Sep;281(2):191-7. doi: 10.1016/0003-9861(90)90431-w.
Complexes exhibiting the characteristics of cooperative interactions are formed by ethidium ion and the self-complementary dinucleoside monophosphates CpG and GpC. Complex formation, observed with an ethidium ion selective electrode, can be described by an equilibrium binding model in which complexes are formed with dinucleoside:ethidium combining ratios of 2:1, 2:2, and 2:3. The total amount of ethidium bound in 2:2 and 2:3 complexes, as calculated from the model, is proportional to a circular dichroism band in CpG-ethidium spectra near 305 nm. Van't Hoff analysis of the model equilibrium constants reveals that the addition of ethidium ion to the 2:1 and 2:2 species is exothermic and that the corresponding entropy changes are large and negative. Cooperative interactions in the binding of ethidium ion and of other ligands to some natural and synthetic polymeric nucleic acids have now been observed in several laboratories, but the present work shows that the effect can arise even with nucleic acid fragments as small as dinucleosides. Apparently, a macromolecular nucleic acid is not essential for cooperative interactions.
乙锭离子与自身互补的二核苷单磷酸CpG和GpC形成了具有协同相互作用特征的复合物。用乙锭离子选择性电极观察到的复合物形成，可以用一个平衡结合模型来描述，其中复合物以二核苷：乙锭的结合比例为2:1、2:2和2:3形成。根据该模型计算，2:2和2:3复合物中结合的乙锭总量与CpG-乙锭光谱中305nm附近的一个圆二色性带成比例。对模型平衡常数的范特霍夫分析表明，向2:1和2:2物种中添加乙锭离子是放热的，并且相应的熵变很大且为负。现在已经在几个实验室中观察到乙锭离子和其他配体与一些天然和合成聚合核酸结合时的协同相互作用，但目前的工作表明，即使是像二核苷这样小的核酸片段也会产生这种效应。显然，大分子核酸对于协同相互作用不是必需的。
