Liquid-Liquid Extraction of Low Molecular-Weight Proteins by Selective Solubilization in Reversed Micelles

Abstract

The effects of pH and salt concentration on the solubilization of ribonuclease-a, cytochrome-c and lysozyme in Aerosol OT/isooctane reversed micelle solutions have been studied to explore the potential for employing this solvent system in the large-scale recovery and concentration of proteins using liquid extraction. For pH values below the isoelectric point, pI, of the protein, solubilization was high, probably owing to strong electrostatic-interactions between the positively charged proteins and the anionic surfactant heads forming the inner micelle wall. Above the pI, the proteins could not be solubilized, probably because of unfavorable electrostatic repulsions between the like-charged proteins and surfactants. At low ionic strength and neutral pH, complete solubilization of the proteins was observed. As the ionic strength was increased, there was an abrupt decrease in solubilizing power of the reversed micelle solutions; the salt concentration at which this occurred was different for each protein. A mixture of the three proteins was cleanly resolved using a single extraction step and two stripping steps. The conditions in each step were selected according to the results of the single protein extraction studies.