Kinetics of lipase-catalyzed esterification in organic media: Correct model and solvent effects on parameters

The Ping-Pong model (incl. alcohol inhibition) is not the correct model to describe the kinetics of a lipase-catalyzed esterification reaction. The fi rst product, water, is always present at the start of the reaction. This le ads to an equation with one extra parameter. This new equation fits our exp erimental data on the esterification of sulcatol and fatty acids in toluene , catalyzed by Candida rugosa lipase. The new model does not significantly improve the mean square of the Ft; however, using a model which cart be exp ected to be more correct, results in the conclusion that a larger part of t he differences can be explained by substrate solvation. For comparison of t he kinetic constants in different solvents, it is essential to make correct ions for solvation. The deviation from the average corrected kinetic consta nt shows to what extent differences can be explained by substrate solvation and an effect on the enzyme. We have made corrections for solvation with t he new model for the esterification in toluene, hexane, trichloroethane, an d diisopropyl ether. This has resulted in kinetic constants that deviate le ss from the average value (C) 1999 Elsevier Science Inc. All rights reserve d.