Takashima H, Nakanishi M, Tsuboi M
Biochemistry. 1985 Aug 27;24(18):4823-5. doi: 10.1021/bi00339a016.
The kinetics of the hydrogen-deuterium exchange reactions of poly(dA).poly(rU) and poly(rA).poly(dT) has been examined, at pH 7.0 and at various temperatures in the 15-35 degrees C range, by stopped-flow ultraviolet spectrophotometry. For comparison, the deuteration kinetics of poly[d(A-T)].poly[d(A-T)] and poly(rA).poly(rU) has been reexamined. At 20 degrees C, the imino deuteration (NH----ND) rates of the two hybrid duplexes were found to be 1.5 and 1.8 s-1, respectively. These are nearly equal to the imino deuteration rates of poly[d(A-T)].poly[d(A-T)] (1.1 s-1) and poly(rA).poly(rU) (1.5 s-1) but appreciably higher than that of poly(dA).poly(dT) (0.35 s-1). It has been suggested that a DNA.RNA hybrid, an RNA duplex, and the AT-alternating DNA duplex have in general higher base-pair-opening reaction rates than the ordinary DNA duplex. The amino deuteration (NH2----ND2) rates, on the other hand, have been found to be 0.25, 0.28, and 0.33 s-1, respectively, for poly(dA).poly(rU), poly(rA).poly(dT), and poly[d(A-T)].poly[d(A-T)], at 20 degrees C. These are appreciably higher than that for poly(rA).poly(rU) (0.10 s-1). In general, the equilibrium constants (K) of the base-pair opening are considered to be greatest for the DNA.RNA hybrid duplex (0.05 at 20 degrees C), second greatest for the RNA duplex (0.02 at 20 degrees C), and smallest for the DNA duplex (0.005 at 20 degrees C), although the AT-alternating DNA duplex has an exceptionally great K (0.07 at 20 degrees C). From the temperature effect on the K value, the enthalpy of the base-pair opening was estimated to be 3.0 kcal/mol for the DNA.RNA hybrid duplex.
采用停流紫外分光光度法，在pH 7.0以及15至35摄氏度范围内的不同温度下，研究了聚（dA）·聚（rU）和聚（rA）·聚（dT）的氢 - 氘交换反应动力学。为作比较，对聚[d（A - T）]·聚[d（A - T）]和聚（rA）·聚（rU）的氘化动力学进行了重新研究。在20摄氏度时，发现两种杂交双链体的亚氨基氘化（NH→ND）速率分别为1.5和1.8 s⁻¹。这些速率几乎等于聚[d（A - T）]·聚[d（A - T）]（1.1 s⁻¹）和聚（rA）·聚（rU）（1.5 s⁻¹）的亚氨基氘化速率，但明显高于聚（dA）·聚（dT）（0.35 s⁻¹）。有人提出，一般而言，DNA·RNA杂交双链体、RNA双链体以及AT交替的DNA双链体的碱基对打开反应速率高于普通DNA双链体。另一方面，在20摄氏度时，聚（dA）·聚（rU）、聚（rA）·聚（dT）和聚[d（A - T）]·聚[d（A - T）]的氨基氘化（NH₂→ND₂）速率分别为每秒0.25、0.28和0.33次。这些速率明显高于聚（rA）·聚（rU）（0.10 s⁻¹）。一般来说，碱基对打开的平衡常数（K）被认为对于DNA·RNA杂交双链体最大（20摄氏度时为0.05），对于RNA双链体次之（20摄氏度时为0.02），对于DNA双链体最小（20摄氏度时为0.005），尽管AT交替的DNA双链体有一个异常大的K值（20摄氏度时为0.07）。根据温度对K值的影响，估计DNA·RNA杂交双链体碱基对打开的焓为3.0千卡/摩尔。
