THERMODYNAMIC AND KINETIC-PARAMETERS OF LIPASE-CATALYZED ESTER HYDROLYSIS IN BIPHASIC SYSTEMS WITH VARYING ORGANIC-SOLVENTS

Kinetics of lipase-catalyzed hydrolysis of esters were modeled using r eactant activities for aqueous-organic, biphasic systems. By using the rmodynamic activities of the substrates in ordinary rate equations, th e kinetic parameters were corrected for the contribution of substrate- solvent interactions and a uniform quantification of the substrates fo r lipase attached to the interface can be achieved. The kinetic parame ters, on the basis of their thermodynamic activities, should be consta nt in different systems, provided that the solvents do not interfere w ith the binding of the substrates to the enzyme nor affect the catalyt ic mechanism. Experimental and computational methods on how to obtain the thermodynamic activities of the substrates are presented. Initial rates were determined for Pseudomonas cepacia lipase (PcL)-catalyzed h ydrolysis of decyl chloroacetate in dynamic emulsions with various sol vents. The thermodynamic equilibrium and corrected kinetic constants f or this reaction appeared to be similar in various systems. The kineti cs of Pet in an isooctane-aqueous biphasic system could be adequately described with the rate equation for a ping-pong mechanism. The observ ed inhibitory effect of decanol appeared to be a consequence of this m echanism, allowing the backreaction of the decanol with the chloroacet yl-enzyme complex. The kinetic performance of Pet in systems with tolu ene, dibutyl ether, and methyl isobutyl ketone could be less well desc ribed. The possible causes for this and for the remaining differences in corrected kinetic parameters are discussed. (C) 1995 John Wiley & S ons, Inc.