NATURE OF MACROMOLECULAR DENATURATION BY UREA AND OTHER COSOLUTES - EXPERIMENTS ON AGAROSE INTERPRETED WITHIN A LATTICE MODEL FOR ADSORPTION FROM A MIXED-SOLVENT

The effects of added urea and of several other low molecular weight cosolutes (including methylated ureas and alcohols) on the coil-to-helix transition of agarose in aqueous solution have been studied. Both stabilizing and destabilizing effects on the helical state (an increase or a decrease in the transition temperature) were observed, depending on the cosolute. The adsorption of the various cosolutes to agarose has also been investigated, by gel permeation chromatography on an agarose column and a clear correlation is found between the destabilizing (stabilizing) efficiency of a cosolute and its degree of adsorption (desorption) to agarose. A lattice model, in which all pair interactions between the system components are considered is used to analyze the effects of the adsorption/desorption of cosolutes on the conformational equilibria of macromolecules. The important role of solvent-cosolute interactions for the adsorption behavior (and denaturing efficiency) of the cosolute is brought out by this analysis. Thus, the slightly unfavorable urea-water interaction, evidenced by thermodynamic data on the binary system, largely suffices to explain the helix-destabilizing effect of urea on agarose. © 1990 American Chemical Society.