Investigation of molecular motions and interprotein interactions in solutions by NMR and TDDS.

Non-selective NMR relaxation of protein and water protons at various resonance frequencies as well as Time Domain Dielectric Spectroscopy (TDDS) were applied to study the molecular motions in lysozyme and myoglobin solutions. It was found that the correlation function of the protein motion defined by means of all these methods can be presented as a sum of three components having substantially different correlation times. Both NMR and TDDS experimental data were treated on the basis of approach according to which these components of the correlation function correspond to three different kinds of protein motion, namely 1) internal local motion, 2) anisotropic rotational Brownian diffusion and 3) translational Brownian diffusion. According to the hypothesis proposed earlier we suppose that the reason of anisotropy of protein rotation and possibility to detect experimentally the slowest motion (translational diffusion) is the mutual interprotein electrostatic steering. The qualitative consistency between parameters of correlation function obtained from NMR and TDDS and their concentration dependence confirm the validity of the qualitative model of the interprotein electrostatic interactions.