Thermodynamic Study on the Thermal Denaturation of Subtilisin

The thermal denaturation of subtilisin and the effect of hydrated and pH on the denaturation were investigation by differential scanning calorimetry. The experimental results showed that the thermal stability of subtilisin in aqueous solution was higher than that lyophilisate. In the water content range from 5.1 to 10.3 g/g, the temperature, T_d, of denaturation was almost independent of the water content, and the enthalpy, ΔH_d, of denaturation decreased with increase of water content. In the PH 5.6 to 7.5 region, the T_d increased lightly and the ΔH_d decreased with increasing pH value. The ratio of the calorforetric enthalpy to the van’t Hoff enthalpy was 0.95 ± 0.07 for subtilisin lyophilisate and for subtilisin in various aqueous solutions. It indicated that the thermal denaturation of subtilisin corresponds to a two-state transition.