KINETIC-STUDY OF LIPASE-CATALYZED ESTERIFICATION REACTIONS IN WATER-IN-OIL MICROEMULSIONS

The kinetics of the esterification of lauric acid by (-)menthol, catal yzed by Penicillium simplicissimum lipase, was studied in water/bis-(2 -ethylhexyl)sulfosuccinate sodium salt (AOT)/isooctane microemulsions. Due to their low water content, microemulsions assist in reversing th e direction of lipase activity, favoring synthetic reactions. The kine tics of this synthesis follows a Ping-Pong Bi-Bi mechanism. The values of all apparent kinetic parameters were determined. The theoretical m odel for the expression of enzymic activity in reverse micelles, propo sed by Verhaert et al. (Verhaert, R., Hilhorst, R., Vermue, M., Schaaf sma, T.J., Veeger, C. 1990. Eur. J. Biochem. 187: 59-72) was extended to express the lipase activity in an esterification reaction involving two hydrophobic substrates in microemulsion systems. The model takes into account the partitioning of the substrates between the various ph ases and allows the calculation of the intrinsic kinetic constants. Th e experimental results showing the dependence of the initial velocity on the hydration ratio, w(o) = [H2O]/[AOT], of the reverse micelles, w ere in accordance with the theoretically predicted pattern. (C) 1993 J ohn Wiley & Sons, Inc.