LIPASE KINETICS IN ORGANIC-WATER SOLVENT WITH AMPHIPATHIC SUBSTRATE FOR CHIRAL REACTION

Lipase from Pseudomonas cepacia was used for asymmetric hydrolysis of the substrate (+/-)1-chloro-2-acetoxy-3-(1-naphthyloxy)-propane, which is a precursor for (S)-(-)-beta-blocker synthesis. Because this subst rate is insoluble in water and partially soluble in hydrophobic solven ts such as hexane and octane, a mixture of hydrophilic organic solvent s and aqueous buffer was used to study the initial reaction rates. Bec ause of the amphipathic nature of the substrate, it can remain in thre e different forms: (1) monomeric (solution); (2) micellar; and (3) emu lsion, depending on the acetone and substrate concentrations in the me dium. This behavior is presented in a phase diagram. The enzyme was fo und to be active with micelle as well as emulsion form of the substrat e, whereas it showed negligible activity with the monomeric form. Mich aelis-Menten constants were determined experimentally for the emulsion and micellar part of the substrate. The initial rate of hydrolysis (v (0)) goes through a maximum with respect to the acetone content of the mixture. It is due to the combined effect of various factors occurrin g simultaneously with the increase in acetone content in the solvent. These phenomena are discussed based on the interfacial activation of l ipase, deactivation of the enzyme at very high acetone concentration, and increase in critical micelle concentration (CMC) and critical emul sion concentration (CEC) with the increase in acetone content in the s olvent, (C) 1997 John Wiley & Sons, Inc.