The technique is also used to assess the stability of proteins, nucleic acids, and
membranes. For example, the thermogram shown in Fig. 2.16 indicates that the
protein ubiquitin undergoes an endothermic conformational change in which a large
number of non-covalent interactions (such as hydrogen bonds) are broken simultaneously
and result in denaturation, the loss of the protein’s three-dimensional structure.
The area under the curve represents the heat absorbed in this process and can be
identified with the enthalpy change. The thermogram also reveals the formation of
new intermolecular interactions in the denatured form. The increase in heat capacity
accompanying the native → denatured transition reflects the change from a more
compact native conformation to one in which the more exposed amino acid side
chains in the denatured form have more extensive interactions with the surrounding
water molecules.