Phosphorescence evidence for the role of solvent–protein interactions in the energetics of conformational flexibility of liver alcohol dehydrogenase

Abstract

When tryptophyl side chains are hidden within relatively inflexible domains of globular proteins, the lifetime of the phosphorescence from these residues provides a measure of the local conformational flexibility. The phosphorescence decay from the tryptophan buried at the base of the nucleotide-binding domain in horse liver alcohol dehydrogenase was monitored between 1-40.degree. C to determine the energetics associated with the rate of local unfolding. The slow rate at which this process takes place results from a high entropic barrier rather than from the disruption of strong intramolecular interactions. This observation along with the response of the system to solvent perturbations points to the significance of solvent-protein interactions in determining conformational flexibility.