Figure 8.

Segmental vs. localized protein motions. The “fluid-like” case schematically depicts the random diffusive motion of the ligand if the protein behaved as a highly associated fluid in which localized fluctuations permitted ligand access to the entire protein. There would be a distribution of volume changes and escape times characteristic of a diffusive process. The lower, segmental motions depict fluctuations involving correlations over the length scales required to create a contiguous path to void spaces in the protein and the solvent for ligand escape. The dynamics in this case would reflect a thermally activated hopping process with discrete intermediates that would depend on the number of accessible void spaces in the protein.