Proteins exist in a predominately aqueous solvent environment. Hydration of the protein surface significantly affects many aspects of the protein's structure and function; these effects may be related to influences on the internal dynamics of the protein. We are examining the influence of hydration on the internal dynamics of hen egg white lysozyme using room temperature phosphorescence from the intrinsic tryptophan residues; since lysozyme is not phosphorescent in solution, the emission intensity serves as a probe of protein conformational fluctuations. Powders of lyophilized lysozyme are hydrated in situ (in the phosphorimeter) using a flow system that allows for continuous manipulation of relative humidity (RH) over the range from 0.5 to 100%; this system allows us to directly compare intensity differences that result from changes in hydration. Lysozyme phosphorescence intensity decreases monotonically as a function of hydration over the entire accessible RH range; the decrease is not linear but appears to occur in distinct phases. The phosphorescence intensity decays are multiexponential over the hydration range and hydration has the largest influence on the long lifetime component. These studies confirm previous work on the effect of hydration on the internal dynamics of globular proteins.
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