Solubilization limit of lysozyme into DODMAC reverse micelles

Dioctyldimethyl ammonium chloride (DODMAC) was used to form reverse micelles and to extract lysozyme from an aqueous solution into an organic phase. The solubilization behavior of lysozyme into a DODMAC reverse micellar phase was examined in terms of the temperature, the type of cations in the aqueous phase, and the surfactant concentration in the organic phase. Complete removal of lysozyme from the aqueous phase was obtained when the pH was set one unit higher than the pI of the protein. However, it was found that there is a solubilization limit of lysozyme in the organic phase. Not all the lysozyme extracted out of the initial aqueous phase was solubilized into the DODMAC reverse micellar phase, resulting in the formation of white precipitate at the aqueous–organic interface. Temperature has a negligible effect on the solubilization limit of lysozyme. The value of the solubilization limit is a strong function of the type of cations present in the aqueous phase, indicating an important role of lysozyme–cation interactions on the extraction process. An increase in the DODMAC concentration from 100–200 mM resulted in little change in the highest concentration of lysozyme obtained in the organic phase. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 80: 537–543, 2002.