The effects of polyols on the thermal stability of calf thymus DNA

The effects on thermal denaturation of calf thymus DNA (ct-DNA) and its con formational changes induced by the presence in solution of different polyol s, namely glycerol, i-erytritol, L(-) and D(+) arabitol, D-mannitol, D-sorb itol and myo-inositol, have been investigated by means of differential scan ning calorimetry (DSC) and circular dichroism (CD). By increasing the conce ntration of these additives a decrease in both the denaturation enthalpy (D elta(d)H) and temperature of the maximum of the denaturation peak (T-max) o f DNA is observed. The values of these thermodynamic parameters depend on b oth the nature and concentration of the solute. The overall destabilization of DNA molecule has been related to the different capability of polyhydric alcohols to interact with the polynucleotide solvation sites replacing wat er and to the modification of the electrostatic interactions between the po lynucleotide and its surrounding atmosphere of counterions. The particular behaviour of L(-) arabitol, which showed a much greater destabilizing abili ty compared to the other polyols, was further investigated and attributed t o a direct more effective interaction with the double helix of DNA. CD spec tra showed only a slight alteration of DNA-B structure in the presence of a ll the molecules here studied, except for L(-) arabitol where the DNA molec ule seems to undergo a meaningful conformational change. The salt concentra tion dependence of DNA thermal stability in the presence of L(-) arabitol i ndicates a conformational change of polynucleotide towards a more extended conformation. (C) 1999 Elsevier Science B.V. All rights reserved.