CPSA Digest 2003

Day 2

Vendor Session - Drug Discovery Technologies & Applications

Overview of Isothermal Titration Calorimetry and Differential Scanning Calorimetry

Isothermal Titration Calorimetry (ITC) is a thermodynamic technique for defining how substances interact with each other. When substances bind, heat is either generated or absorbed. Measurement of this heat allows one to obtain a full thermodynamic profile that includes: binding constants, reaction stoichiometry, enthalpy ( H), free energy (_G), and entropy ( S). Because heat is naturally absorbed or released during chemical reactions, ITC does not require immobilization and/or modification of reactants. ITC is routinely used to study all types of binding reactions including, antigen-antibody, protein-ligand, protein-protein, DNA-drug, receptor-target, amongst others. ITC has also gained importance and popularity in the measurement of enzyme reactions. Differential Scanning Calorimetry (DSC) is an instrumental method used to measure structural and conformational energy in macromolecules. This is accomplished by "scanning up" in temperature and measuring the difference in heat generated in a sample and reference cell. This heat difference is related to the conformational energy in biological macromolecules such as proteins, membranes, nucleic acids, and others. By determining the different temperatures at which transitions (Tm) occur and the heat capacity ( Cp) of these transitions, much information can be gained regarding the structure of biological macromolecules. By scanning down in temperature, additional information may be gained about the thermal reversibility of biological processes. Typical applications for DSC include, elucidation of thermally induced structural transitions, estimation of formulation stability, chemical half-life studies, solution optimization for crystal growth, and a few others. MicroCal has also pioneered the use of pressure perturbation calorimetry. This accessory to the DSC allows for the experimental measurement of volumetric properties of proteins and other biopolymers in dilute solutions.

Return to Proceedings »