Polymer-Induced Phase Separation in Aqueous Micellar Solutions of Alkylglucosides for Protein Extraction

Aqueous micellar solutions of alkylglucosides were separated into two phases at 0°C upon addition of polyethylene glycol 6000 (PEG) or Dextran T-500 (Dextran). One was an aqueous phase in which hydrophilic proteins, cytochrome c and peroxidase (horseradish), were retained, and the other was a surfactant-rich phase into which hydrophobic membrane proteins, bacteriorhodopsin and cytochrome b5, were extracted. A combination of octyl-β-D-thioglucoside (OTG) (or nonyl-β-D-glucoside (NG)) with PEG (or Dextran) was the best choice for extraction of hydrophobic proteins. Extraction yields (50-90%) and concentration factors (7-30) of the hydrophobic proteins were dependent on the types of nonionic surfactants and water-soluble polymers. Solubilization and phase separation in processing cell membranes could be made in a single step at 0°C. Hence the present method would be useful for the purification of thermolabile proteins