Isothermal Titration Calorimeter
Isothermal titration calorimetry measures the heat that is released (or required) when molecules interact. In a typical ITC experiment, a single titration of ligand into a solution of its interaction partner results in a series of peaks representing the heat of each addition. These can be analysed to give a complete characterization of binding thermodynamics, i.e. the binding affinity, stoichiometry, enthalpy and entropy.
A wide range of buffer conditions are suitable. A further advantage is that molecules do not need to be labelled or altered, so the method lends itself to investigations at native conditions. However, a relatively large sample volume is required, so alternatively Surface Plasmon Resonance could be used, or, if one of the binding partners is fluorescent, anisotropy measurementscould be performed.
Differential Scanning Calorimeter
Differential scanning calorimetry enables accurate measurement of temperature dependent properties. The stability of a structure can be investigated, the melting temperature and the complete thermodynamics of melting can be determined.
Applications include the examination of complex stabilities or the influence of ligand binding on the stability of a macromolecule.
Also for DSC, the solution conditions can be readily altered to allow determination of the pH or salt dependence of thermodynamic quantities. Alternatively, CD spectroscopy measures the melting of structures using their optical characteristics, and the Thermofluor Assay might serve as a much higher throughput method to screen various conditions.