THERMODYNAMICS OF HELIX-COIL EQUILIBRIUM IN OLIGOADENYLIC ACID FROM HYPOCHROMICITY STUDIES
THERMODYNAMICS OF HELIX-COIL EQUILIBRIUM IN OLIGOADENYLIC ACID FROM HYPOCHROMICITY STUDIES
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DOI：
10.1021/ja01085a007
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发表时间：
1965-01-01
影响因子：
15
通讯作者：
DAMLE, V
中科院分区：
文献类型：
--
作者：
APPLEQUIST, J;DAMLE, V
The theory of helix-coil equilibria has been applied to hypochromicity studies of oligoadenylic acids. Com-puter methods were used to solve equations relating the two fundamental equilibrium constants needed to de-scribe the process to the measured hypochromicities. From the temperature dependence of the stability con-stant for base pairing, the enthalpy of the base pairing reaction was found to be—8.0 kcal. jmole of base pairs, and the entropy—21 cal.¡ deg.¡ mole of base pairs, both quantities being constant to within 10% for oligomers of eight to eleven residues. The association factor, which is the additional factor in the equilibrium constant for formation of the first base pair between two strands, was found to be 2.2 X 70-3 l./mole. Good agreement between. theoretical and experimental hypochromic “melt-ing'” curves was obtained for oligomers of two to eleven residues only when the following contributions to hypo-chromicity were incorporated in the theory:(i) the dependence of hypochromicity on helix length predicted by Rich and Tinoco and (ii) a temperature dependence of hypochromicity of nonbonded bases proposed to account for anomalous behavior of the melting curves toward the hightemperature end. The observed agree-ment is taken to be support for the existence of both effects and particularly for the hypothesis that interactions between neighboring base pairs are responsible for hypochromism inthe helix.
