Measurement of intermediate exchange phenomena.

Understanding the crucial role of protein motions in the function of biological macromolecules requires methods for their characterization. These motions lead to noticeable alterations in the decay of nuclear spin magnetization. Recent advances in solution nuclear magnetic resonance (NMR) make quantitative connections between micro s-ms motions and nuclear spin relaxation in proteins. The techniques serve as useful probes of motional kinetics and thermodynamics and their relation to function. Here, we review the two most common experimental methods for characterizing conformational motions in proteins: the relaxation-compensated Carr-Purcell-Meiboom-Gill (rcCPMG) and off-resonance R1rho experiments.