EPR spin-labelling and spin-trapping study of proteins in reverse micelles

Abstract

EPR spectroscopy has been used to study the motions of several spin-labelled and spin-trapped proteins (α-chymotrypsin, cytochrome c and myoglobin) enclosed within reverse micelles formed by sodium bis-(2-ethylhexyl) sulfosuccinate (AOT) in isooctane. In several cases the spectra obtained from the encapsulated protein are significantly different from those observed in bulk solution. The motions of the labelled proteins, inferred from the anisotropy of the EPR spectra (A_‖ values), vary with the amount of solubilized water (W₀) and hence the physical size of the water-pool in the reverse micelles; it is suggested that the level of solvation and the solvent structure in the water-pool of the reverse micelle cause the observed changes in motion. These results support the previously postulated ‘water-shell’ model of proteins contained in reverse micelles.