聚（5-甲基脱氧鸟苷-脱氧胞苷）中B型到Z型转变的热力学
Thermodynamics of the B to Z transition in poly(m5dG-dC).
作者信息
Chaires J B, Sturtevant J M
出版信息
Proc Natl Acad Sci U S A. 1986 Aug;83(15):5479-83. doi: 10.1073/pnas.83.15.5479.
Differential scanning calorimetry, temperature-dependent absorbance, and circular dichroic spectroscopy were used to study the thermodynamics of the B-Z transition in poly(m5dG-dC). In sodium phosphate buffer (pH 7.0) containing 50 mM NaCl and 1.0 mM MgCl2, the reversible B-Z transition of the polymer is centered at 38.2 degrees C and is characterized by delta Hcal = 0.61 +/- 0.07 kcal/(mol X base pair) (1 cal = 4.184 J), delta HvH = 68 +/- 7 kcal/mol, and a cooperative unit of length 110 +/- 20 base pairs. A second transition centered at 53.6 degrees C is observed and represents a conformational change of poly(m5dG-dC) from the Z to an alternate left-handed form of unknown structure. This transition does not arise from aggregation to the Z form, or from the helix-coil transition. The left-handed helix-coil transition is observed at 120.9 +/- 0.3 degrees C and is characterized by delta Hcal = 9.1 +/- 1.0 kcal/(mol X base pair). These results indicate a substantial enthalpic contribution to the B-Z transition, in contrast to previous assertions that the process is entropically driven.
采用差示扫描量热法、温度依赖吸光度和圆二色光谱法研究了聚（m5dG-dC）中B-Z转变的热力学。在含有50 mM NaCl和1.0 mM MgCl2的磷酸钠缓冲液（pH 7.0）中，该聚合物的可逆B-Z转变以38.2℃为中心，其特征为ΔHcal = 0.61±0.07 kcal/（mol×碱基对）（1 cal = 4.184 J），ΔHvH = 68±7 kcal/mol，协同单元长度为110±20碱基对。观察到以53.6℃为中心的第二个转变，它代表聚（m5dG-dC）从Z构象转变为未知结构的另一种左手形式。这种转变不是由聚集成Z构象或螺旋-卷曲转变引起的。左手螺旋-卷曲转变在120.9±0.3℃观察到，其特征为ΔHcal = 9.1±1.0 kcal/（mol×碱基对）。这些结果表明，与之前认为该过程是由熵驱动的观点相反，B-Z转变有很大的焓贡献。
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