Hagmar P, Pierrou S, Nielsen P, Nordén B, Kubista M
Department of Physical Chemistry, Chalmers University of Technology, Gothenburg, Sweden.
J Biomol Struct Dyn. 1992 Feb;9(4):667-79. doi: 10.1080/07391102.1992.10507947.
The binding of the intercalating dye methylene blue (MB) to chromatin and to free DNA has been studied as a function of ionic strength at very low binding ratios (1 MB/400 DNA bases) using absorption spectroscopy. With increasing salt concentration MB is displaced from chromatin to a higher extent than from DNA. The free energy change for MB binding to chromatin is found to be approximately 5 kJ/mole lower than for binding to DNA. This difference can be explained by the reduced number of high affinity binding sites in chromatin due to the presence of histone proteins. The difference in binding energy is virtually independent of the degree of chromatin condensation and also of the valence of counter ions, suggesting that neither the affinity for, nor the number of intercalation sites in the linker DNA is markedly changed upon the salt-induced condensation. The unaffected thermodynamics of the linker binding suggests that factors such as DNA superhelicity and the electrostatic influence from the chromatosomes remain unchanged during chromatin condensation.
利用吸收光谱法，在非常低的结合比（1个亚甲蓝/400个DNA碱基）下，研究了嵌入染料亚甲蓝（MB）与染色质和游离DNA的结合情况与离子强度的关系。随着盐浓度的增加，MB从染色质上被取代的程度比从DNA上被取代的程度更高。发现MB与染色质结合的自由能变化比与DNA结合的自由能变化低约5 kJ/摩尔。这种差异可以通过由于组蛋白的存在，染色质中高亲和力结合位点数量减少来解释。结合能的差异实际上与染色质凝聚程度以及抗衡离子的价数无关，这表明在盐诱导的凝聚过程中，连接DNA对嵌入的亲和力和嵌入位点数量均未发生明显变化。连接结合的热力学未受影响表明，诸如DNA超螺旋性和来自染色小体的静电影响等因素在染色质凝聚过程中保持不变。
