Enzyme dynamics and activity: Time-scale dependence of dynamical transitions in glutamate dehydrogenase solution

We have examined the temperature dependence of motions in a cryosolution of the enzyme glutamate dehydrogenase (GDH) and compared these with activity. Dynamic neutron scattering was performed with two instruments of different energy resolution, permitting the separate determination of the average dy namical mean square displacements on the sub-similar to 100 ps and sub-simi lar to 5 ns time scales. The results demonstrate a marked dependence on the time scale of the temperature profile of the mean square displacement. The lowest temperature at which anharmonic motion is observed is heavily depen dent on the time window of the instrument used to observe the dynamics. Sev eral dynamical transitions (inflexions of the mean squared displacement) ar e observed in the slower dynamics. Comparison with the temperature profile of the activity of the enzyme in the same solvent reveals dynamical transit ions that have no effect on GDH function.