Lipase-catalyzed synthesis of isoamyl butyrate - A kinetic study

Kinetics of lipase-catalyzed esterification of butyric acid and isoamyl alc ohol have been investigated. The reaction rate could be described in terms of the Michaelis-Menten equation with a Ping-Pong Bi-Bi mechanism and compe titive inhibition by both the substrates. No evidence of any significant di ffusional limitations was detected that could affect the kinetics. The valu es of the apparent kinetic parameters were computed as: V-max=11.72 mu mol/ min/mg; K-M. Acid =0.00303 M; KM. Alcohol = 0.00306 M; K-i. Acid = 1.05 M; and K-i. Alcohol = 6.55 M. This study indicates a competitive enzyme inhibi tion by butyric acid during lipase-catalyzed esterification reaction. Butyr ic acid, being a short-chain polar acid, concentrates in the microaqueous l ayer and causes a pH drop in the enzyme microenvironment leading to enzyme inactivation. Butyric acid binds to acyl-enzyme complex unproductively to y ield a dead-end intermediate that can no longer give rise to an ester. High concentration of butyric acid gave rise to inactivation of the biocatalyst in addition to dead-end inhibition. (C) 2001 Elsevier Science B.V. All rig hts reserved.