[Thermal denaturation of pepsin in crystal form and in solution]

Thermal transitions in pepsin crystals were studied by scanning microcalorimetry and microscopy. A sharp dependence of thermal transition parameters upon the heating rate was discovered. It was determined that during the heating of pepsin crystals it is possible to observe phase transition of the first order type. Thermal transition is connected only with the denaturation of protein molecules in the crystal. The absence of crystals melting was shown with the help of microscopy. The coincidence of equilibrium denaturation temperatures of pepsin in crystal and in solution was shown in direct calorimetric experiments. The results obtained point to the fact that intermolecular interactions do not give any contribution to the thermostability of hydrated supermolecular protein systems.