Nuclear magnetic relaxation dispersion in monoclinic lysozyme crystals

Nuclear magnetic relaxation measurements are reported as a function of field strength corresponding to the frequency range from 0.01 to 20 MHz for water protons in monoclinic lysozyme crystals at 278 and 298 K. Though the instrumentation used selects only a portion of the total magnetization to sample, the data clearly indicate a field dependence of the relaxation rate that signals the presence of slow motions characterized by time constants in the range of tenths of microseconds and slower. The data support, but do not uniquely prove, the hypothesis that this time scale is that appropriate to the isotropic averaging of locally anisotropic water molecule motion at the protein surface.