[Study of water-protein interaction by high resolution NMR]

The interaction between carbonic anhydrase B in the molten globule state and water molecules was studied by high-resolution NMR spectroscopy. NMR spin diffusion experiments revealed spin diffusion propagation from the protein to waters. This is a process of complex bioexponential kinetics presented in spin diffusion spectra as a change in water signal intensity dependent on the post-excitation time of protein molecules. Its reverse, spin diffusion propagation from waters to the protein, was also found. These phenomena are protein concentration- and temperature-dependent and shown to be possibly explained with the assumption that there exist water-protein complexes provoking the formation of large branched associations. At a temperature above 309 K, a stepwise increase in the interaction between waters and proteins occurs in these complexes. The formation of water-protein associations is induced by increasing temperature and/or protein concentration. In these associations, at normal temperature, the protein mobility is close to that of carbonic anhydrase B dimers.