Heat denaturation of ribonuclease under high pressure: Differential scanning microcalorimetry study

Abstract

Scanning microcalorimetry was used to study heat denaturation of ribonuclease A at high pressure. The pressure dependences of temperature and enthalpy of denaturation were measured at two levels of pH. It was shown that pressure destabilizes the RNase structure and significantly reduces the enthalpy of denaturation. Pressure does not affect the cooperativity of transition. The results allowed estimating of the partial increment of volume ΔVm as well as increments of isothermal compressibility and thermal expansibility associated with denaturation. Increasing pressure increases the magnitude of the volume increment ΔVm. The second-order pressure derivatives of ΔVm must be taken into account to retrieve dependencies between temperature / enthalpy of denaturation vs. pressure. Proportional change of ΔVm and its partial derivatives with respect to pressure and temperature provides a basis for approximation of experimental data. The nature of the volume increment decrease accompanying the denaturation of proteins and the driving mechanism of the change of denaturation enthalpy with increasing pressure are discussed.