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Isothermal Titration Calorimetry (ITC) is a powerful analytical tool that allows the measurement of binding affinities and of their related thermodynamic parameters. ITC directly measures the heat released or absorbed during molecular binding. Measurement of this heat enables direct accurate determination of a number of thermodynamic parameters in a single experiment: binding affinity (KD), stoichiometry (n), enthalpy (ΔH). From the former and the latter of these parameters we can derive as well the entropy (ΔS) of the reaction.

This technology presents a wide range of applications including the characterization of molecular interactions involving small molecules, proteins, antibodies, nucleic acids, lipids, metal ions, etc. ITC is as well useful in enzyme kinetics and inhibition/competition studies. No labeling or immobilization are required and there are almost no buffer restrictions.

We use an iTC200 system from Microcal (GE Healthcare), one of the most sensitive isothermal titration calorimeters available. The sample cell is only 200 µL. It can directly measure sub-millimolar to nanomolar binding constants (10-7 to 10-9 M-1). Measure of nanomolar to picomolar binding constants (10-9 to 10-12 M-1) is also possible by using the competitive binding technique.

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