The most extensive evidence for this mechanism emerges from correlations between changes in NMR order parameters and calorimetry measurements. This correlation has been most extensively studied by Wand and colleagues in calmodulin, which binds various peptides with roughly similar overall binding affinity, but each with distinct entropic and enthalpic profiles. For example, upon binding a peptide derived from smooth muscle myosin light chain kinase peptide (smMLCKp), the receptor loses side chain conformational entropy, especially around the smMLCKp binding site . This result agrees with the direction and magnitude of the estimate of residual conformational entropy from calorimetry. In a series of papers, the authors extended this work to six peptides, each with similar affinity to calmodulin . The contribution of conformational entropy to the binding affinity of these peptides varies widely, ranging from highly favorable to highly unfavorable. In each case, the average change in side chain NMR order parameters correlated with the estimates from calorimetry, leading to the concept of the 'entropy meter' (Figure ).