[Heat capacity of hydrated and dehydrated globular proteins. The denaturing increment of heat capacity]

Absolute values of heat capacity for some hydrated globular proteins (11S globulin, ovalbumin, ribonuclease A, and lysozyme) have been studied by differential scanning calorimetry. It has been found that for proteins with bound water, as in the case of protein solutions, the heat capacity of denatured proteins is higher then prior to denaturation. Depending on temperature and humidity, the denatured proteins can be either in high-elastic or glass state. Specific heat capacities for these two states have the same values for all proteins and depend only on temperature with a characteristic increment of 0.55 J.g-1.K-1 at glass transition. The glass transitions were observed not only in denatured but also in native proteins. Our results indicate that the main contribution to the heat capacity increment at denaturation is connected with the thermal motion in the protein globule, which is contrast with the commonly accepted ideas.