Kinetics of Some Selected Enzyme-Catalysed Reactions in Organic Solvents
Kinetics of few selective enzymatic esterification and glycosylation reactions in organic solvents is discussed. In all the kinetics, initial rates were determined, and from the pattern of the double reciprocal plots of 1/[S] versus 1/v, appropriate kinetic models were identified and the equations worked out. Iterative procedures adopted to carry out curve-fitting of the experimental plots resulted in determination of the four kinetic parameters K i, K mA, K mB and k cal corresponding to the best fit. All the enzymes studied showed Ping-Pong Bi-Bi mechanism. In the enzymatic esterification reaction between l-alanine and d-glucose in dichloromethane, d-glucose was found to be inhibitory to both Rhizomucor miehei lipase and Candida rugosa lipase. However, both l-phenylalanine and d-glucose in dichloromethane solvent were found to exhibit competitive double substrate inhibition of Rhizomucor miehei lipase, leading to dead-end inhibition by RML–d-glucose complex and RML–l-phenylalanyl complexes. On the other hand, esterification of l-phenylalanine with d-glucose using Candida rugosa lipase in dichloromethane showed that only d-glucose functions as a competitive inhibitor forming dead-end CRL–d-glucose complex.
Similarly, kinetics of glucosylation was investigated in detail for the glucosylation of curcumin and vanillin using amyloglucosidase in di-isopropyl ether solvent. Both kinetics could be best described by the Ping-Pong Bi-Bi model with a single competitive substrate inhibition by respective curcumin and vanillin of amyloglucosidase leading to dead-end inhibition. Observed kinetic picture was explained in terms of the active site geometry and the geometry of binding of the substrate/s to the enzyme.
KeywordsDouble Reciprocal Plot Candida Rugosa Lipase Menten Constant Specific Reaction Rate Rhizomucor Miehei Lipase
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