Solution behavior of α‐chymotrypsin dissolved in nonpolar organic solvents via hydrophobic ion pairing

Dissolution of α‐chymotrypsin in nonpolar organic solvents can be achieved using hydrophobic ion pairing, whereby the polar counterions are replaced by a stoichiometric number of detergent molecules. Using Aerosol OT[AOT, sodium bis(2‐octyl)sulfosuccinate], it is possible to partition significant amounts of the enzyme into alkanes and chlorocarbons. Apparent solubility in isooctane is greater than 1 mg/mL (80 μM). Necessary conditions for achieving effective partitioning of α‐chymotrypsin into these solvents are described. Using CD spectroscopy, it can be shown that the AOT–α‐chymotrypsin (CMT) complex retains its native secondary and tertiary structure when dissolved in alkanes, and that the globular structure is stable to more than 100°C. In contrast, α‐chymotrypsin unfolds at 54°C in aqueous solution. The relative solubility of the AOT–CMT complex in a variety of alkanes and chlorocarbons is also reported. The native structure of α‐chymotrypsin is maintained in carbon tetrachloride, but not in methylene chloride or chloroform. © 1995 John Wiley & Sons, Inc.