Volume 6, Number 1, p.p. 25-30
Calorimetric studies of the thermal denaturation of salmon sperm DNA in aqueous solutions of urea and guanidinium chloride
Ekaterina Tabuashvili, George Getashvili, Maya Makharadze, Lia Tsulukidze, Rusudan Sujashvili and Dimitri E. Khoshtariya
Laboratory of Biochemical Kinetics and Thermodynamics, Institute of Molecular Biology and Biological Physics, Georgian
Academy of Sciences, 12 Gotua St, 0160 Tbilisi, Georgia
The differential scanning calorimetry (DSC) technique was applied for the first time to comparative studies of DNA thermal melting in the presence of urea and guanidinium chloride (GuHCl) over extended ranges of the cosolute concentrations. Precise values of the thermodynamic parameters, calorimetric melting temperature (Tm) and enthalpy (ΔHcal), and preliminary data analysis, are presented. Both compounds display an overall destabilizing effect. An odd coincidence has been observed for the dependencies of ΔHcal on the concentration of both cosolutes up to 6 M (in 0.1 M NaCl as supporting electrolyte). This and other findings (viz., dissimilarities in Tm patterns) are tentatively interpreted in terms of the entropy-driven partly stabilizing binding of GuH+ ions in the minor groove of the native DNA duplex (vs a negligible binding effect for urea), and the similarity of favourable enthalpydriven hydrogen-bonding interactions for both species with the exposed (amide-like) polar groups in the single-stranded (melted) DNA.
Keywords: destabilizing effect, differential scanning calorimetry, DNA, guanidinium chloride, hydrogen bonding, minor groove, thermal melting, thermodynamic parameters, urea