The role of conformational energetic disorder in the catalytic activity of immobilized enzymes

We analyze cooperative behavior in a system of immobilized enzymes which incorporates the notion of heterogeneity or disorder in the interactions. In addition to equilibrium phase changes, this system exhibits vitrification or glass-like transitions in which the overall catalytic activity freezes into one of many possible states. It is shown that these long-lived metastable phases can be produced by a combination of disorder, systematic surface and intermolecular interactions, and chemical association effects such as ligand binding. Biophysical consequences of this frozen state include greatly diminished sensitivity of enzymatic activity to thermal and chemical perturbations. This effect coincides with the appearance of a multitude of possible macroscopic catalytic states rather than a single equilibrium state. Our analysis also suggests that high surface coverages will tend to be catalytically inactive if they are fully equilibrated; rather, high activity with high surface coverage is more likely to be associated with vitrified states of surface immobilization and deep or abrupt chemical quenches.