Protein extraction using reversed micelles
Proteins can be extracted from an aqueous phase into reversed micelles. This transfer is governed by electrostatic interactions, for protein and surfactant have to bear opposite charges. The presence of high salt concentrations diminishes the attractive interactions and can lead to expulsion of the solubilized proteins. This is used to recover extracted proteins. Larger proteins require a larger number of charged residues on their surface in order to be transferred into reversed micelles, so the larger the protein, the further the pH of maximal transfer is removed from the isoelectric point. The transfer profiles can be manipulated by micellar size and charge density at the interface. When the charge density at the interface is modified by variation of the type of head group of the cosurfactant, shifts of transfer profiles to higher or lower pH values are observed. Variation of the number and length of the tails of quaternary ammonium surfactants revealed that of the 16 surfactants tested, only didecyldimethyl ammonium chloride and trioctylmethylammonium chloride enabled transfer. There was no relation between the water content of the organic phase and the transfer properties of the surfactants tested. Because for application not only forward transfer is important, an alternative method for back transfer was tested. Exposing an enzyme containing reversed micellar solution to a temperature increase led to expulsion of aqueous phase and enzyme, yielding a highly concentrated enzyme preparation.