Torigoe H, Shimizume R
Tsukuba Life Science Center, Institute of Physical and Chemical Research (RIKEN), 3-1-1 Koyadai, Tsukuba, Ibaraki 305-0074, Japan.
Nucleic Acids Symp Ser. 2000(44):61-2. doi: 10.1093/nass/44.1.61.
We analyzed the thermodynamics of purine motif triplex formation by isothermal titration calorimetry. The signs of calorimetric enthalpy change, delta Hcal, and entropy change, delta S, of the triplex formation were negative in the temperature range between 15 and 35 degrees C. Since an observed negative delta S was unfavorable for the triplex formation, the triplex formation was driven by a large negative delta Hcal. delta Hcal decreased with increasing temperature, yielding a negative heat capacity change, delta Cp, of approximately -1.2 kcal mol-1 K-1. We found that the binding constant, Ka, increased with increasing temperature, leading to an apparent positive van't Hoff enthalpy change, delta Hvh, which was in sharp contrast with the large negative delta Hcal. The analyses of the observed temperature dependence of Ka and delta Hcal and the negative delta Cp suggest that the purine motif triplex formation near room temperature is not a simple two-state binding process but exhibits multiple states, which was previously observed for the pyrimidine motif triplex formation near room temperature.
我们通过等温滴定量热法分析了嘌呤基序三链体形成的热力学。在15至35摄氏度的温度范围内，三链体形成的量热焓变（ΔHcal）和熵变（ΔS）的符号均为负。由于观察到的负ΔS不利于三链体形成，因此三链体形成是由大的负ΔHcal驱动的。ΔHcal随温度升高而降低，产生约 -1.2 kcal mol-1 K-1的负热容变化（ΔCp）。我们发现结合常数（Ka）随温度升高而增加，导致明显的正范特霍夫焓变（ΔHvh），这与大的负ΔHcal形成鲜明对比。对观察到的Ka和ΔHcal的温度依赖性以及负ΔCp的分析表明，室温附近的嘌呤基序三链体形成不是一个简单的二态结合过程，而是表现出多种状态，这与之前在室温附近观察到的嘧啶基序三链体形成情况相同。
