[Equilibrium intramolecular mobility in proteins].

The critical analysis of available information on equilibrium intramolecular mobility in proteins is performed and an attempt is made to systematize it in relation to characteristic times tau, probability and spatial scale. We propose to discriminate fast (tau less than 10(-6) s) and slow (tau greater than 10(-6) s) mobility. The methods are considered for investigating fast mobility (X-ray analysis temperature-dependent factor, broadening of absorption spectra, thermal perturbation difference spectra and thermal ring-current shifts of 1H-NMR, fluorescence dipolar relaxation and quenching, 13C-NMR spin-lattice relaxation times and nuclear Overhauser enhancement and others) and the principal results obtained. Fast mobility is widely spread within the molecules. Its existence results in a population of dynamic microstates, the distribution of which depends on local packing density and secondary bonding. The fast movements are local and of very small activation energies. tau depends on the group size and are much longer than those of diffusion in simple liquids. Therefore, this kind of mobility may be characterized as a limited diffusion process in a medium with high and nonuniform viscosity. The significance of the fast mobility for the protein function is discussed. No function significant transglobular change of protein conformation could be obtained by subnanosecond, fast movements, but they depend on the level of "viscosity' of protein interior, produced by fast mobility. The fast dynamic microstates results in distribution of activation parameters for protein reactions.