Thermodynamic activity-based enzyme kinetics: Efficient teal for nonaqueous enzymology

Lipase-catalyzed synthesis reactions must be performed in nonaqueous media (organic solvents or solvent-free systems). The choice of the optimal solve nt is usually, a fastidious task that necessitates the determination of kin etic parameters in each solvent. The approach used here, to overcome the la ck of a model that can pr edict the kinetics whatever the solvent, consists in the use of thermodynamic activities instead of concentrations of compon ents, and assumes that activity-based kinetic parameters are the same in al l solvents. This assumption is discussed, and a solution is proposed which takes into account some observed residual solvent effects. The reaction cho sen to test this approach was the esterification of oleic acid with ethanol catalyzed by an immobilized lipase, Lipozyme. For this reaction, the kinet ics predicted in various organic solvents and in solvent-free systems is in agreement with the experimental data.