Continuous Isothermal Titration Calorimetry-cITC-a new way to speed up and improve binding experiments Natalia Markova Dan Hallen Biovitrum AB, Stockholm, Sweden INTRODUCTION Microcalorimetric instruments and methods are now essential tools for the generalunderstanding of binding thermodynamics of biological macromolecules and specific bio-logical systems. Provided that the enthalpy of binding is of appropriate magnitude, it ispossible to determine affinities, K , in the order of 10 nM (K=10"M') for 1:1 complexes.One of the most important issues with ITC is the time needed to obtain a full binding iso-therm. ITC inherently suffers from the relatively small number of binding experimentsthat are possible to perform per day. The focus has so far been on improving calorimetricresponse time of the instruments by various means, like assigning instrumental time con-stants and applying Tian’s equation to dynamically correct the raw calorimetric signal froma fast step-wise titration . Notably,nothing has so far been done to improve the experimen-tal procedure. At the moment 2-3 h is needed to complete an ITC binding experiment. Thenumber of data points that can be obtained, 20-30 points, limits the range of equilibriumconstants that can be resolved from the data. For ITC this range is 1