Comparisons of pressure and temperature activation parameters for amide hydrogen exchange in T4 lysozyme

Activation enthalpies and entropies are reported for proton-deuteron exchange at 42 amide sites in T4 lysozyme and compared with activation volumes for the same residues obtained earlier [Hitchens, T. K., and Bryant, R, G. (1998) Biochemistry? 37, 5878-5887]. There is no correlation found between activation volume and activation entropy or activation enthalpy, The activation enthalpy is linearly related to the activation entropy in part as a consequence of a relatively narrow sampling window for the rate constants that corresponds to a narrow range of activation free energy. A consequence of the entropy-enthalpy compensation is preservation of rank order of proton exchange. Variations in Delta H double dagger, Delta S double dagger, and Delta V double dagger for residues that are structurally close together in the folded protein suggest that there may be a variety of energetically distinct pathways for the access of solvent to these structurally related exchange sites.