Abstract
High-sensitivity differential scanning calorimetry (HSDSC) is widely used to examine the thermal behaviour of biomolecules and water-soluble polymers in aqueous solution. The principal purpose of this manuscript is to examine the thermodynamic basis for the signals obtained using HSDSC. It is shown that a combination of the van’t Hoff isochore and Kirchhoff’s equation are all that is necessary to simulate and curve fit the HSDSC output obtained for the thermally induced unfolding of the protein ubiquitin. The treatment is further developed to show how the temperature dependence of the heat capacity change of unfolding, multiple sequential transitions, and protein dissociation can be incorporated into the thermodynamic description of protein unfolding and how these factors in turn affect the HSDSC signal.
Highlights
High-sensitivity differential scanning calorimetry (HSDSC) is widely employed for the study—in aqueous solution—of the thermodynamic parameters associated with processes initiated either by an increase in temperature or by a decrease in temperature
Biopolymers in aqueous solution, such as proteins, which are cooperatively stabilised by numerous weak forces, can be examined by HSDSC
HSDSC can be used to examine: 1. Transitions from the physiologically active native form of a protein through intermediate partially unfolded states to the final denatured form of the protein. Very often, such a process is characterised by minimally populated intermediate states and approximates to a two-state transition between the initial native form and the final denatured form of the protein [1]
Summary
High-sensitivity differential scanning calorimetry (HSDSC) is widely employed for the study—in aqueous solution—of the thermodynamic parameters associated with processes initiated either by an increase in temperature (up-scan) or by a decrease in temperature (down-scan). Transitions from the physiologically active native form of a protein through intermediate partially unfolded states to the final denatured form of the protein Very often, such a process is characterised by minimally populated intermediate states and approximates to a two-state transition between the initial native form and the final denatured form of the protein [1]. In HSDSC, the specific heat of an aqueous system is measured as a function of temperature. Because the quantity (S - S1) is usually very small, a differential mode of measurement [solvent (reference cell) versus solvent plus solute (sample cell)] has to be used. Given that a major portion of the specific heat change is due to the heating and cooling of the solvent (usually water which has a large heat capacity), it is essential to have a differential arrangement, so that phase transitions in the solute can be observed
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