Enhanced solubility of proteins and peptides in nonpolar solvents through hydrophobic ion pairing
A new technique for enhancing the solubility of peptides and proteins in organic solvents is described. Complexation of polypeptides with stoichiometric amounts of an anionic detergent, such as sodium dodecyl sulfate (SDS), produces diminished aqueous solubility, but enhanced solubility in organic solvents. Consequently, the partitioning of a polypeptide into a nonpolar solvent can be increased by two to four orders of magnitude. In the case of an insulin–SDS complex, the solubility in 1-octanol is more than tenfold greater than in water. In 1-octanol, the native structure of insulin remains intact, as determined by CD spectroscopy, and the thermal denaturation temperature (Tm) is increased by approximately 50°C relative to unfolding in water. Finally, peptides and proteins can be extracted back into an aqueous phase provided the chloride concentration is sufficient to displace bound detergent molecules. © 1993 John Wiley & Sons, Inc.