Park Y W, Breslauer K J
Department of Chemistry, Rutgers, State University of New Jersey, New Brunswick 08903.
Proc Natl Acad Sci U S A. 1991 Feb 15;88(4):1551-5. doi: 10.1073/pnas.88.4.1551.
We have calorimetrically detected and energetically characterized a premelting event in the "bent" duplex [d(GA4T4C)]2 that is absent in the "normal" duplex [d(GT4A4C)]2. This premelting may correspond to the thermally induced "unbending" of the duplex. Specifically, we have used a combination of spectroscopic and calorimetric techniques to evaluate whether differences in the electrophoretic and hydrogen exchange properties of the bent duplex, [d(GA4T4C)]2, and the normal duplex, [d(GT4A4C)]2, are paralleled by differences in the equilibrium melting properties of these duplexes. Our results reveal that the bimolecular global meltings of both duplexes exhibit two-state behavior and are characterized by the expected thermodynamic changes, as well as the expected salt-dependencies. Significantly, however, at temperatures below duplex melting and over a similar temperature range in which the aberrant electrophoretic mobility is observed (approximately less than 35 degrees C), the bent duplex exhibits calorimetric premelting behavior absent in the normal duplex. Analysis of the calorimetric data in this preglobal melting domain (approximately less than 35 degrees C) allows us to estimate a lower-limit value of 1.6 kcal/(mol-base pair) for the thermally induced unbending of the decameric duplex.
我们通过量热法检测并从能量角度表征了“弯曲”双链体[d(GA4T4C)]2中的预熔解事件，而“正常”双链体[d(GT4A4C)]2中不存在该事件。这种预熔解可能对应于双链体的热诱导“伸直”。具体而言，我们结合了光谱和量热技术，以评估弯曲双链体[d(GA4T4C)]2和正常双链体[d(GT4A4C)]2在电泳和氢交换特性上的差异是否与这些双链体平衡熔解特性的差异相对应。我们的结果表明，两种双链体的双分子整体熔解均表现出二态行为，其特征在于预期的热力学变化以及预期的盐依赖性。然而，值得注意的是，在双链体熔解温度以下且在观察到异常电泳迁移率的相似温度范围内（约低于35摄氏度），弯曲双链体表现出正常双链体中不存在的量热预熔解行为。对该预整体熔解域（约低于35摄氏度）中的量热数据进行分析，使我们能够估计出十聚体双链体热诱导伸直的下限值为1.6千卡/（摩尔碱基对）。
