LASER TEMPERATURE-JUMP STUDY OF STACKING IN ADENYLIC ACID POLYMERS
LASER TEMPERATURE-JUMP STUDY OF STACKING IN ADENYLIC ACID POLYMERS
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DOI：
10.1021/bi00593a002
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发表时间：
1979-01-01
期刊：
影响因子：
2.9
通讯作者：
TURNER, DH
中科院分区：
文献类型：
--
作者：
DEWEY, TG;TURNER, DH
用激光温度跳跃法研究了腺苷酸聚合物单链堆积的动力学。该技术允许在0.05 M离子强度下测定聚核糖腺苷酸[poly（A）]、核糖腺苷酸七聚体和聚脱氧核糖腺苷酸[poly（dA）]的速率常数。在这种低离子强度下，观察到含氟聚合物的单一的、与波长无关的弛豫。热力学由通过UV吸收测量的熔融曲线的分析确定。通过假设2-态模型，计算了在25 ° C下形成堆叠态的速率常数。poly（A）和poly（dA）的C为0.7 × 10 - 4。107和2.7 ×107 s-1。反向速率常数为3.2 × 10 - 4。聚（A）为106 s-1，聚（A）为4.3 × s-1。106 s-1的聚（dA）。聚（A）的正向速率活化能为4.0 kcal/mol，反向速率活化能为15.2 kcal/mol。聚（dA）具有类似的正向速率活化能3.2 kcal/mol和较低的反向速率活化能12.3 kcal/mol。核糖七聚体结果与聚（A）类似。考虑到低活化能垒，正向速率常数相对较小。这被解释为对活化熵的构象效应。在0.2 M离子强度和0、2或5 mM Mg 2+下，聚（A）表现出对弛豫时间的波长依赖性。这表明存在两个以上的国家。在这些高盐浓度下，弛豫时间比在0.05 M离子强度下长。这被解释为拆垛速率的降低。因此，高盐似乎使堆叠状态稳定。
The kinetics of the single-strand stacking of adenylic acid polymers were investigated by using the laser temperature-jump method. This technique allowed the determination of rate constants for polyriboadenylic acid [poly(A)], the riboadenylic acid heptamer and polydeoxyriboadenylic acid [poly(dA)] at 0.05 M ionic strength. At this low ionic strength a single, wavelength-independent relaxation is observed for the ribopolymers. The thermodynamics were determined from an analysis of the melting curves measured by UV absorption. By assumption of a 2-state model, the rate constants for formation of the stacked state at 25.degree. C for poly(A) and poly(dA) are 0.7 .times. 107 and 2.7 .times. 107 s-1, respectively. The reverse rate constants are 3.2 .times. 106 s-1 for poly(A) and 4.3 .times. 106 s-1 for poly(dA). The activation energy for poly(A) was 4.0 kcal/mol for the forward rate and 15.2 kcal/mol for the reverse rate. Poly(dA) has a similar activation energy of 3.2 kcal/mol for the forward rate and a lower reverse rate activation energy of 12.3 kcal/mol. The ribo heptamer results are similar to poly(A). The forward rate constants are relatively small considering the low activation barriers. This is interpreted as a conformational effect on the activation entropy. At 0.2 M ionic strength with 0, 2 or 5 mM Mg2+, poly(A) exhibits a wavelength dependence to the relaxation time. This indicates the presence of more than 2 states. At these high salt concentrations, the relaxation times are longer than at 0.05 M ionic strength. This is interpreted as a decrease in the rate of unstacking. Thus, high salt appears to stabilize the stacked state.