Thermodynamic approach to protein denaturation

DSC allows direct measurement of the enthalpy change related to the denaturation process this property can be referred to as the excess average enthaly AH(T) , referred to a particular thermodynamic state (the native state) and averaged on all the accessible macroscopic states at a given temperature T. This definition does not imply any particular model or mechanism for the specific process considered. A general relationship of statistical thermodynamics states that  

When a thermodynamic analysis can be applied (proteins in dilute solutions), the DSC trace allows an assessment (see Appendix A4.1) of if the denaturation process can be referred to as a one step reversible process [168-170], namely  

The following quantities can be thence evaluated across the N D transition  

If AdCp is constant, the function corresponds to a straight line. 

A Hfl) of many globular proteins was found to have this behaviour, although with a slope that depends on the specific protein [171], If the specific enthalpy values (i.e., the values calculated per gram of protein) are plotted versus 7, the various straight line iH(T) trends converge toward a single point at about 7 = 383 K [172,173], A similar situation was found with the entropy functions, 

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In the analysis of the energetics of protein denaturation, knowledge of the structure of the unfolded state is as important as the knowledge of the native one. The thermodynamical approach to protein denaturation usually assumes that the result of denaturation is the complete exposure to the solvent of all the amino acid residues and peptide bonds, which means that the unfolded state is one single population of highly expanded, fully solvated and disordered conformations, whatever the protein, the denaturation process, or the solvent conditions considered. 

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