The quantitative comparison of the effects of denaturants on the stability of proteins

A novel quantitative comparison of denaturants involving the complete reversible unfolding of proteins is presented. Ribonuclease A was denatured with guanidinium chloride in the presence of low fixed concentrations of various partial denaturants, with the unfolding process being monitored by circular dichroism and difference spectroscopy. The major advantage of this method is that it allows a direct quantitative comparison of the effects of denaturants on the stability of proteins. The effect on the stability of ribonuclease A was shown to be linearly dependent upon the concentration of denaturant. An investigation of the constitutive ions of salts revealed that their effects were additive only in the case of salts that have no specific binding capability. This method can also be useful in detecting the specific binding of salts.