Rapid energy exchange of enzymes with solvent water by dipolar interaction.

One important problem for the function of proteins, especially enzymes, concerns the exchange of energy with the surrounding medium. In this paper, we study the interaction of vibrational degrees of freedom with the fluctuating water dipole moments. The rates of activation or deactivation attain a maximum at slow frequency vibrations near the water dispersion frequencies, i.e. in the gigahertz region. For medium proteins with molecular weights of approximately 10(4) a.m.u., the rates are estimated to be of the order of magnitude of kBT/h, the frequency factor of the transition state theory. We discuss the connection between energy exchange and reaction rates and show that a rapid energy exchange is at least a necessary condition for enzymatic catalysis.