Extraction of cytochrome c in sodium dodecylbenzenesulfonate microemulsions

The partition of cytochrome c between an aqueous phase in equilibrium with a microemulsion composed of sodium dodecylbenzenesulfonate, butanol, and decane was studied. By adjusting the pH and the ionic strength in the aqueous phase, cytochrome c can be quantitatively extracted in the microemulsion as long as the protein concentration in the organic phase is less than the initial concentration of micelles. Above this limit, an intermediate phase, containing part surfactant and part cytochrome c, is located between the aqueous and microemulsion phases. The role of electrostatic interactions in the protein partitioning is shown by varying the composition of the phases (pH, salinity, surfactant, and cosurfactant concentrations) and then discussed. Extraction depends on the relative values of the pH of the aqueous phase and the pI of cytochrome c, the size of the micelles, and the protonation of acidic residues. Cytochrome c can be recovered in an aqueous phase by adding butanol in the microemulsion phase. In such conditions, cytochrome c retains 90% of its initial activity, as measured before the extraction step.