Effect of Hydration on the Thermal Stability of Protein as Measured by Differential Scanning Calorimetry

The thermal denaturation of chymotrypsinogen A was investigated by differential scanning calorimetry in the water-content range 0.09 -1.46 g water per g protein. At water contents above 0.82 g/g, the temperature, Td, and the enthalpy, delta Hd, of denaturation were almost independent of the water content. At lower water contents, however, both Td and delta Hd showed marked dependence on the water content. The Td increased with a decrease in the water content, whereas the delta Hd decreased with a decrease in the water content in the same region. The degree of hydration dependency of delta Hd exhibited a break at approximately 0.41 g/g, which indicated that at least two types of hydration phase contributed to the thermal stability of the protein. This behavior was similar to that noted for lysozyme.