Biocalorimetry: Differential Scanning Calorimetry of Protein Solutions
The term biocalorimetry refers to the application of calorimetry to the study of the energetics of biological processes. Current high-sensitivity commercially available calorimeters offer the possibility of using small sample volumes of very dilute solutions and are able to directly measure very small amounts of heat, which allow the analysis of the thermodynamics of non-covalent interactions, such as those involved in biological macromolecules. This chapter presents an overview of the most relevant applications of DSC to protein solution studies. A survey of the main theoretical models to interpret and analyze protein calorimetric thermograms is described, together with an evaluation of their applicability. Here the main goal of DSC is to characterize protein stability and analyze protein thermal unfolding. From the DSC measurements all the meaningful thermodynamic parameters of such processes, together with the temperature-dependent population of the initial, final and possible intermediate states can be determined. The wider possibilities of DSC to investigate the effect of protein self-association as well as that of the presence of protein ligands during the thermal processes are also described. Finally, when the unfolding process does not occur under equilibrium, DSC is also a very useful technique to study protein denaturation through a kinetic approach.