Specific heat upon aqueous unfolding of the protein interior: a theoretical approach

We study theoretically the thermodynamics, over a broad temperature range (5–125°C), related to hydrated water upon protein unfolding. The hydration effect is modeled as interacting dipoles in an external field, mimicking the influence from the unfolded surfaces on the surrounding water compared to bulk water. The heat capacity change upon hydration is compared with experimental data from Privalov and Makhatadze on four different proteins: myoglobin, lysozyme, cytochrome c and ribonuclease. Despite the simplicity of the model, it yields good correspondence with experiments. With some interest we note that the effective coupling constants are the same for myoglobin, lysozyme, and cytochrome c, although they are slightly different for ribonuclease.