Separation of Proteins by a Liquid Membrane with Reverse Micelles

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Liquid-liquid extraction of proteins into an organic phase containing Aerosol-OT (AOT) in isooctane was studied for lysozyme (L), ribonuclease-A (R) and alpha-chymotrypsin. These proteins are most significantly extracted in the reverse micelles (RM) below their isoelectric points, when positively charged and at low ionic strength. The distribution equilibria were explained in terms of two effects : an electrostatic interaction between the charged protein and AOT headgroups, and size exclusion effect due to water pool of the RM. The amount of water solubilized into the surfactant solution was corredated with both concentrations of the salt and AOT. It was found that the RM solution saturated with proteins has a limiting content which depends only on the water content of the organic phase.The rate of mass transfer in the extraction of lysozyme between an aqueous phase and the RM solution was studied using a stirred cell. Forward transfer of the protein from the aqueous to the RM phase occurs in the pH range 4-9.2 ; the rate was found to be controlled by the diffusion of the protein through the aqueous boundary film. Backward transfer from the RM to the aqueous phase occurs at the values above 11. In contrast to the forward transfer, this process is controlled by the interfacial process of protein release from the RMs. Further study was made on the separation of L and R by use of a liquid membrane cell. It was found that the separation factor of L can attain to 954. This suggests that liquid membranes containing the RMs have a potential application for the separation and concentration of proteins from aqueous solutions. In addition, studies were made on the distribution of iodine between the bulk solution and water pool of the RM in the organic phase, the denaturation of lysozyme during extraction by the RM, and the purification of trypsin from an extract of porcine pancreas by use of the RMs.