Abstract
Abstract The fluorescence properties of indole derivatives, lysozyme and azurin were investigated in reverse micelles of detergent sodium bis[2-ethylhexl]sulfosuccinate (Aerosol OT)* in n-hexane. L-tryptophan, l-methyl-tryptophan and n-acetyl-l-tryptophanamide exhibited complex fluorescence decays in reverse micelles. Fluorescence decays were best described using Gaussian bimodal distributions of lifetimes. Increasing hydration levels in the micelles resulted in a decrease in decay heterogeneity, as indicated by a large decrease in lifetime distribution widths. Steady-state polarization and fluorescence emission measurements indicated both an increase in average polarity of the environment around the indole derivatives and an increase in the mobility of the probes with increasing hydration levels. The fluorescence decays of lysozyme and azurin in reverse micelles were also found to be very complex and were described with Gaussian lifetime distributions. Increasing water content in the micelles caused marked decreases in both center and width of the lifetime distributions for these two proteins. Steady-state polarization measurements as a function of the extent of hydration revealed an increase in the average rotational rates of the tryptophan residues in lysozyme upon increasing water content. Thus, static polarization and lifetime measurements indicate that the amount of water present in the micelle may influence the amount of structural flexibility of the polypeptide chains and the rates of interconversion between conformational substates.
Highlights
The first comprehensive review on protein motions was by Careri, Fasella and Gratton
The underlying idea of that work was that hydration of the protein matrix is required for most protein motions and that the network of hydration would serve as a common medium for the connection between solvent and protein dynamics
The major results are that (1) motions occur over a very wide time scale; (2) a given kind of motion can occur over a very wide time scale, i.e., kinetics are non-exponentials; (3) protein structure and dynamics are hierarchically organized; (4) proteins of a given type may have the same average structure but each individual molecule may be different in its fine structure; and (5) small differences in the structure can result in large differences in function
Summary
The first comprehensive review on protein motions was by Careri, Fasella and Gratton (ref. 1). The major results are that (1) motions occur over a very wide time scale 4); (2) a given kind of motion can occur over a very wide time scale, i.e., kinetics are non-exponentials; (3) protein structure and dynamics are hierarchically organized Despite the amount of research and the advances on protein dynamics, there are still some basic aspects that need to be understood Among those aspects is the role of hydration. The effect of hydration on protein dynamics has been addressed very little in published literature and its physical origin is virtually unknown. This investigation presents a study of protein hydration using reverse micelles, which can contain a single protein molecule in a microscopic pool. We present the relevant information on the use of reverse micelles for hydration studies
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