Heat of the reaction forming the three‐stranded poly (A + 2U) complex
Heat of the reaction forming the three‐stranded poly (A + 2U) complex
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形成三链聚 (A + 2U) 复合物的反应热
DOI：
10.1002/bip.1965.360030410
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发表时间：
1965
期刊：
影响因子：
2.9
通讯作者：
R. Scruggs
中科院分区：
文献类型：
--
作者：
P. Ross;R. Scruggs
在24 ° C和37°C下，在0.1M和0.5M NaCl中，将聚U的第二链添加到聚（A +2U）以形成三链聚（A + 2U）复合物的热量的量热测量。本文报告ΔH值= −3800 cal./发现所形成的聚（A + 2U）的摩尔数对所采用的实验条件相当不敏感。将第三链添加到预先形成的聚（A + U）螺旋的热量比聚A和聚U之间形成聚（A + U）的反应热量要小得多。第三条链（polyU）的加成热对盐浓度和温度的变化不敏感，这为先前的假设提供了定性支持，即polyA和polyU反应的ΔH随实验条件的变化主要来自polyA构象的差异。将本研究中获得的关于形成poly（A + 2U）的反应的ΔH的信息与关于形成poly（A + U）的ΔH的数据相结合，表明poly（A + U）向poly（A + 2U）的转化与随温度增加的焓变相反。将这些值外推至52°C。其中在0.5M NaCl中poly（A + U）转化为poly（A + 2U），导致ΔH = +3800 cal/生成的摩尔（A + 2U）和ΔS = 11.5 cal./形成的（A + 2U）摩尔。由量热数据推断，聚（A + U）到聚（A + 2U）转化反应的驱动力是有利的熵变。
Calorimetric measurements of the heat of the addition of the second strand of poly U to poly (A + 2U) to form the three‐stranded poly (A + 2U) complex in 0.1M and 0.5M NaCl at 24 and 37°C. are reported. A value of ΔH = −3800 cal./mole of poly (A + 2U) formed was found to be fairly insensitive to the experimental conditions employed. The heat of the addition of the third strand to the preformed poly (A + U) helix is considerably less exothermic than the heat of reaction between poly A and poly U to form poly (A + U). The insensitivity of the heat of addition of the third strand (poly U) to changes in salt concentration and temperature lends qualitative support to the earlier hypothesis that the major portion of the variation of the ΔH of the poly A and poly U reaction with experimental conditions arises from differences in the conformation of poly A. Combining the information obtained in this study for the ΔH of the reaction forming poly (A + 2U) with data for the ΔH of the formation of poly (A + U) indicates that the conversion of poly (A + U) to poly (A + 2U) is opposed by an enthalpy change which increases with temperature. Extrapolation of these values to 52°C. where poly (A + U) is transformed to poly (A + 2U) in 0.5M NaCl leads to a value of ΔH = +3800 cal./mole (A + 2U) formed and ΔS = 11.5 cal./mole of (A + 2U) formed. It is concluded from the calorimetric data that the driving force for the poly (A + U) to poly (A + 2U) conversion reaction is the favorable entropy change.