Effects of protein solubilization on the structure of the surfactant shell of reverse micelles

The influence of protein encapsulation in the water pool of the reverse micelles has been studied by the electron spin resonance (ESR) spin-label technique and electrical conductivity measurements. For this purpose water-sodium-bis(2-ethylhexyl)-sulfosuccinate (AOT)-decane water-in-oil microemulsions with solubilized trypsin were used. The ESR data, obtained with the help of 4-(2-n-undecyl-3-oxyl-4,4,-dimethyloxazolidin-2-yl) butyric acid as a label, show that the protein molecule encapsulated in the water core of a reverse micelle forces a portion of water out from the aqueous core into the hydrophobic shell of a micelle. As a result, changes in the packing of AOT hydrocarbon chains and in the polarity of their microenvironment are induced. The effect of the encapsulated protein depends on the difference in the sizes of the protein molecule and the micelle aqueous core. The perturbations in the dynamic structure of the surfactant shell turn out to be most pronounced when the dimensions of the water cavity are close to the size of the protein molecule. The solubilization of protein in the reverse micelles results in remarkable variations in mass exchange between micelles.