Isothermal titration calorimetry (ITC) is a powerful technique used to study molecular interactions by measuring the heat released or absorbed during a titration. In ITC, a small amount of one solution containing a molecule of interest (usually a biomolecule) is incrementally added to a larger solution containing the other molecule of interest (usually a ligand) while the temperature is held constant. The heat released or absorbed during each addition is measured and used to calculate the binding affinity, stoichiometry, and thermodynamics of the interaction.
ITC works on the principle that binding between two molecules leads to a change in enthalpy (∆H), which can be measured by monitoring the heat flow. The change in enthalpy is related to the binding affinity of the interaction by the equation:
ΔG = -RT ln(K)
where ΔG is the change in free energy, R is the gas constant, T is the absolute temperature, and K is the equilibrium constant. By measuring the heat flow during each titration, the values of ∆H and K can be calculated, which can be used to determine the thermodynamic parameters ΔG and ΔS.
ITC is widely used in biochemical and biophysical research to study a wide range of molecular interactions, including protein-ligand binding, DNA-protein binding, enzyme-substrate binding, and antibody-antigen binding. It is a label-free technique that does not require any modifications or labeling of the molecules of interest, making it a powerful tool for studying biological systems in their native state.