Thermodynamic characterization of the partially denatured states of ribonuclease A in calcium chloride and lithium chloride
The denaturations of ribonuclease A by calcium chloride and lithium chloride were studied by circular dichroism measurements in the far-ultraviolet region. The temperature dependence of the equilibrium constant for the unfolding of the protein by calcium chloride and lithium chloride gave values of 46 and 52 kcal mol−1 (1 cal = 4.1868 J) for the enthalpy of denaturation at 25 °C and pH 7.0, respectively. Thermodynamic parameters for the denaturation by calcium chloride and lithium chloride are compared with those for the heat and guanidine hydrochloride denaturation. It has been observed that the thermodynamic quantity, be it free energy, entropy, or enthalpy, cannot be related quantitatively to the extent of unfolding measured by various conformational properties of the protein.
Free energy changes in denaturation of ribonuclease A by mixed denaturants. Effects of combinations of guanidine hydrochloride and one of the denaturants lithium bromide, lithium chloride, and sodium bromide.
