PROTEIN BACKBONE FLUCTUATIONS AND NMR FIELD-CYCLING RELAXATION SPECTROSCOPY

Proton and deuteron field-cycling relaxation spectroscopy has been employed for the characterization of fluctuations in proteins and in their hydration shells. The nature of the fluctuations is shown to be different. Deuteron relaxation dispersion of water in particular does not reflect the dynamics specific for protein backbones. Protein backbone fluctuations are characterized by simple power laws describing the overall frequency dependence of the spin-lattice relaxation time over several decades. The exponent changes at about 200 K from a constant value above this temperature to values decreasing with decreasing temperatures. This may be interpreted by a transition from ergodic to nonergodic behavior in the time scale of the experiments. © 1990 American Chemical Society.