Direct measurement of protein binding energetics by isothermal titration calorimetry

Of all the techniques that are currently available to measure binding, isot hermal titration calorimetry is the only one capable of measuring not only the magnitude of the binding affinity but also the magnitude of the two the rmodynamic terms that define the binding affinity: the enthalpy (DeltaH) an d entropy (DeltaS) changes. Recent advances in instrumentation have facilit ated the development of experimental designs that permit the direct measure ment of arbitrarily high binding affinities, the coupling of binding to pro tonation/deprotonation processes and the analysis of binding thermodynamics in terms of structural parameters. Because isothermal titration calorimetr y has the capability to measure different energetic contributions to the bi nding affinity, it provides a unique bridge between computational and exper imental analysis. As such, it is increasingly becoming an essential tool in molecular design.