9), and stabilization of the transition state by interaction Spectroscopic techniques (UV absorbance, circular dichroism, with the surfactant head groups (10). Changes in microenvifluorescence emission and anisotropy, and light scattering) were ronment can also lead to changes in substrate specificity due used to investigate enzyme solubilization in Aerosol-OT (AOT) to partitioning effects (6, 11,12).
reversed micelles in which a bile salt, sodium taurocholate Among the amphiphiles capable of forming reversed mi-(NaTC), is used as a novel cosurfactant. NaTC significantly incelles, Aerosol-OT (AOT) has received particular attention creases the water capacity and size of the reversed micelles through because of its ability to solubilize relatively large amounts surfactant reorganization. The solubilization of several enzymes, of water in a variety of organic solvents. We are interested including lysozyme, chymotrypsin, lipase, lipoxidase, carbonic anin the construction of microreactors for enzymatic reactions hydrase, and ribonuclease A, was demonstrated. These enzymes, ranging in mass from 10 4 to 10 5 Da, are incorporated in the mi-based on a four-component system in which a bile salt is celles in stable, optically transparent solutions. Several other proused as a novel cosurfactant in AOT reversed micelles. Bile teins were not successfully solubilized. The presence of NaTC in salts are important biological detergents which participate in the reversed micelles significantly altered the conformations of the many physiological processes, such as intestinal hydrolysis, solubilized enzymes, apparently by promoting unfolding of the dispersion and digestion of lipids, cholesterol solubilization, enzyme through interactions with the interior micellar interface. and drug absorption (13-16). According to the monolayer Lysozyme and lipase respond to solubilization in the AOT/NaTC solubilization model ( 17), bile salts would be expected to micelles by altering their conformations to accommodate the miact as cosurfactants primarily by increasing the area per cellar structure. The effect of NaTC is greatest for lysozyme, inducsurfactant molecule at the reversed micellar interface.
ing a higher degree of order and helicity in the enzyme structure.
The size of the aqueous pool in simple AOT reversed
Chymotrypsin, on the other hand, disrupts the micellar structure micelles is primarily controlled by the water/AOT ratio and reorganizes the surfactants to accommodate its own preferred conformation. Addition of NaTC to the reversed micelles causes (v 0 ). Our previous work has shown that sodium taurocholate a 3-fold increase in the enzymatic activity of solubilized chymo-(NaTC), which is a trihydroxy bile salt, serves as an effectrypsin. แญง 1997 Academic Press tive cosurfactant in AOT reversed micelles by substantially Key Words: reversed micelles; enzyme solubilization; bile salts. increasing the water solubilization capacity of the system and the size of the reversed micelles through surfactant reorganization (18). By adding NaTC, we were also able to alter
MATERIALS AND METHODS