Dynamic and Exchange Processes in Macromolecules Studied by NMR Spectroscopy

It is normal for a biological system to be in a dynamic state. The function of many biological systems depends on their flexibility, and here NMR can provide the experimental basis for investigating the mechanical function of such systems. The types of motions that are thought to occur in proteins, their frequency ranges, and the methods for their detection are summarized in Table 1 . It is important to distinguish ubiquitous thermal vibrations or group rotations from the more extensive motions that can be propagated through larger segments of a structure. Motions and dynamics are reflected by five different NMR parameters: chemical shift, spin-spin coupling constant, the area enclosed by a resonance, relaxation time, and nuclear Overhauser effect (1 ). The NMR data can be used to provide either qualitative evidence of flexibility or quantitative measurements of exchange rates.