A Convenient tool for studying the stability of Proteins and Nucleic Acids

The aim of this work is to discuss the thermodynamic properties, obtained by differential scanning calorimetry (DSC), of the thermal transition of proteins and nucleic acids and to analyze these data using statistical thermodynamic relations. The denaturation of the ordered, specific structures of biological macromolecules is a cooperative process and in many cases the macromolecules undergo a two-state transition. Differential scanning calorimetry, giving direct thermodynamic information, has proved to be very useful in clarifying the energetics of macromolecule transitions and in characterizing their thermal stability. Here, various examples are discussed: i) the equilibrium thermal denaturation of ribonuclease A, a model for the use of DSC by following the temperature-unfolding of the proteins, a monomolecular transition; ii) the equilibrium thermal dissociation of a DNA double helix in two strands, an example of how DSC is used to follow a bimolecular process; iii) an example of the use of DSC for studying the melting of unimolecular and tetramolecular DNA quadruple-helices.