Quantum Behavior of Water Protons in Protein Hydration Shell

Abstract

Quantum effects on the water proton dynamics over the surface of ahydrated protein are measured by means of broadband dielectricspectroscopy and deep inelastic neutron scattering. Dielectricspectroscopy indicates a reduced energy barrier for a hydrogenatedprotein sample compared to a deuterated one, along with a large andtemperature-dependent isotopic ratio, in good agreement withtheoretical studies. Recent deep inelastic neutron scattering data havebeen reanalyzed, and now show that the momentum distribution of waterprotons reflects a characteristic delocalization at ambienttemperatures. These experimental findings might have far-reachingimplications for enzymatic catalysis involving proton transferprocesses, as in the case of the lysozyme protein studied in thisreport.