EPR SPIN-LABELING AND SPIN-TRAPPING STUDY OF PROTEINS IN REVERSE MICELLES

EPR spectroscopy has been used to study the motions of several spin-la belled and spin-trapped proteins (alpha-chymotrypsin, cytochrome c and myoglobin) enclosed within reverse micelles formed by sodium bis-(2-e thyl-hexyl) sulfosuccinate (AOT) in isooctane. In several cases the sp ectra obtained from the encapsulated protein are significantly differe nt from those observed in bulk solution. The motions of the labelled p roteins, inferred from the anisotropy of the EPR spectra (A(parallel t o) values), vary with the amount of solubilized water (W-0) and hence the physical size of the water-pool in the reverse micelles; it is sug gested that the level of solvation and the solvent structure in the wa ter-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.