THERMODYNAMICS OF THE B TO Z TRANSITION IN POLY(M5DG-DC)
THERMODYNAMICS OF THE B TO Z TRANSITION IN POLY(M5DG-DC)
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DOI：
10.1073/pnas.83.15.5479
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发表时间：
1986-08-01
影响因子：
11.1
通讯作者：
STURTEVANT, JM
中科院分区：
文献类型：
--
作者：
CHAIRES, JB;STURTEVANT, JM
Differential scanning calorimetry, temperature-dependent absorbance, and circular dichroic spectroscopic 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.degree. C and is characterized by .DELTA.Hcal = 0.61 .+-. 0.07 kcal/(mol .cntdot. 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.degree. 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.degree. C and is characterized by .DELTA.Hcal = 9.1 .+-. 1.0 kcal/(mol .cntdot. 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.
