THE OBSERVED CHANGE IN HEAT-CAPACITY ACCOMPANYING THE THERMAL UNFOLDING OF PROTEINS DEPENDS ON THE COMPOSITION OF THE SOLUTION AND ON THE METHOD EMPLOYED TO CHANGE THE TEMPERATURE OF UNFOLDING

The apparent change in heat capacity, Delta C-p, accompanying the ther mally induced unfolding of lysozyme and of ribonuclease A was determin ed by means of differential scanning calorimetry in dilute aqueous buf fer containing one of the following added solutes: 0.5 M or 1.0 M sucr ose, 1.0 M glycine, 0.5 M, 1.0 M, or 2.0 M guanidinium chloride, 10% g lycerol, or 0.5 M NaCl over a pH range. In each system the temperature of half-completion, t(1/2), of the unfolding transition was varied by varying the pH. The resulting enthalpies of denaturation were linearl y dependent on t(1/2) for each solvent system. The resulting values of Delta C-p for each protein showed variations of almost 2-fold. Such l arge variations in the sensitivity of the proteins to temperature chan ges are not readily interpreted.