Reformulated Kinetics of Immobilized Enzymes in Non-Conventional Media: A Case of Lipase-Catalyzed Esterification

Several approaches have been reported that aim to achieve simplified standardizations of the kinetic behavior of immobilized enzymes under specific experimental conditions. We have previously published simplified rate equations based on the kinetics of immobilized enzymes. Recently, new experimental results have become available on the kinetics and mechanisms of esterifications catalyzed by immobilized lipase in unconventional media, and consequently, a reformulation of their kinetics is necessary. In this work, we report the development of simplified rate equations relating the aforementioned reaction conditions on a new basis, considering our kinetic and mechanistic results. We provide experimental evidence that two different mechanisms describe the esterifications catalyzed by immobilized lipase, either in anhydrous organic solvent (n-hexane) or under non-solvent conditions. A ping-pong bi–bi mechanism with double dead-end substrate inhibition by both the fatty acid and the alcohol has been found to apply in the former case, while in the latter case the esterification proceeds via an ordered bi–bi mechanism with single dead-end substrate inhibition by ethanol. This study may be biotechnologically useful, as the increased use of immobilized enzymes, whether in academic research or in industry, requires sustainable development of new and environmentally friendly synthetic processes.