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Quantitative test of Record's theory for proton‐induced lowering of DNA melting temperature
Author(s) -
Mingot Francisco
Publication year - 1981
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.1981.360201007
Subject(s) - chemistry , protonation , counterion , enthalpy , sodium , proton , thermodynamics , atmospheric temperature range , melting temperature , counterion condensation , condensation , computational chemistry , ion , organic chemistry , physics , materials science , quantum mechanics , composite material
This report presents a quantitative test of the ability of the counterion condensation theory to describe the proton‐induced lowering of DNA melting temperature. From a general approach of Record et al. [Record, M. T., Anderson, C. F. & Lohman, T. H. (1978) Q. Rev. Biophys. 11 , 103–178], we have obtained an expression that may be computer‐fitted to the experimental data by numerical minimization of χ 2 . To do this, in addition to the assumptions made by Record et al., it was necessary to suppose that the interchange between protons and sodium is independent of pH and, due to the absence of data, take the enthalpies of protonation as thermally independent over the experimental temperature range. The dependences of the enthalpy of denaturation at neutral pH on sodium concentration and on G + C content were taken from literature. In the fitting process we have used 250 melting temperatures obtained at different pH and sodium concentrations for various natural DNAs. The theoretical expression gives a good quantitative description of the G + C and sodium concentration influences on the phenomenon but is only qualitative with respect to the dependence of dT / d log[Na + ] on the pH. The adjusted p K values for the bases in denatured DNA agree with those for isolated deoxynucleosides. Interchange between sodium and protons is found to be less than 1:1. Calculated protonation enthalpies are ill‐defined because of their low numerical influence. In short, it appears that the theory gives a good description of most of the aspects of the phenomenon even if it has some shortcomings, perhaps due to the great number of assumptions.