Denatured increments of heat capacity in globular proteins and its connection with vitrification processes

Absolute values of heat capacity for some hydrated globular proteins have been studied by differential scanning calorimetry (DSC) method. It has been found that for the proteins with completely bound water, like in the case of protein solutions, the value of heat capacity of denatured proteins is higher than that 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.K. at glass transition. The glass transitions were observed not only in denatured but also in native proteins. As it follows from our results, the main contribution to the heat capacity increment at denaturation is connected with the thermal motion in the protein globule which is in contrast with the commonly accepted ideas.