Tight ligand binding affinities determined from thermodynamic linkage to temperature by titration calorimetry

A general isothermal titration calorimetry method is described that can be used to determine equilibrium binding constants for high-affinity interactions of ligands with biological macromolecules. The method exploits the thermodynamic linkage between the ligand binding equilibrium constant and temperature. By measuring the binding enthalpy change for an interaction as a function of temperature directly, the change in affinity can be calculated with an integrated form of the van't Hoff equation that is applicable to ligand binding to biological macromolecules. When the temperature dependence of the affinity is combined with the absolute affinity determined independently at a convenient temperature (where the affinity can most accurately or most easily be measured), the absolute binding affinity over the entire temperature range is determined.