THE EFFECT OF PH ON THERMAL-STABILITY OF GLOBULAR-PROTEINS - A CRITICAL INSIGHT

In this study we try to re-analyze the pH dependence of thermal stabil ity of small globular proteins. From the thermodynamic point of view a long series of calorimetric and spectroscopic investigations has show n that the decreased stability in very acidic conditions can be ascrib ed to entropic effects. The same conclusion is reached, from a microsc opic point of view, by assuming that a binding of protons on equal and noninteracting sites takes place as a consequence of unfolding proces s. By linking the conformational unfolding equilibrium to the proton b inding equilibrium, a model is developed that is able to describe the dependence on the pH of the thermal denaturation processes of small gl obular proteins. The application of the model to hen lysozyme and T4 l ysozyme correctly accounts for the experimental results.