Alcoholysis catalysed by Candida antarctica lipase B in a gas/solid system obeys a Ping Pong Bi Bi mechanism with competitive inhibition by the alcohol substrate and water (original) (raw)
Related papers
Organic Synthesis with Enzymes in Non-Aqueous Media
The influence of the addition of an extra component in a gaseous reaction medium, on the kinetics of alcoholysis of methyl propionate and n-propanol catalyzed by immobilized lipase B from Candida antarctica was studied in a continuous solid/gas reactor. In this reactor, the solid phase is composed of a packed enzymatic sample which is percolated by gaseous nitrogen, simultaneously carrying gaseous substrates and additional components to the enzyme while removing reaction products. The system permits to set thermodynamic activity of all gaseous components (substrates or not) independently at the desired values. This allows in particular to study the influence of an extra added component at a constant thermodynamic activity value, contrary to classical solid/liquid system, which involves large variations of thermodynamic activity of added solvent, when performing full kinetic studies. Alcohol inhibition constant (K I) and methyl propionate and propanol dissociation constants (K MP and K P) have been determined in the solid/gas reactor in presence of 2-methyl-2-butanol, and compared with values previously obtained in absence of added component and in presence of water. Complementary experiments were carried out in the presence of an apolar compound (hexane) and led to the conclusion that the effect of added organic component on lipase catalyzed alcoholysis is related to their competitive inhibitory character towards first substrate methyl propionate. The comparison of data obtained in liquid or with gaseous 2-methyl-2-butanol shows that lower K MP and K I are found in gaseous medium, which would correspond on the one hand to a lower acylation rate k 2 , and on the other hand to a higher binding rate k 1 between substrate and free enzyme in gaseous medium.
Journal of Molecular Catalysis B: Enzymatic, 2004
The feasibility of the enzymatic enantioselective acylation of R-2-pentanol in a solid/gas reactor was demonstrated and compared to the same reaction carried out in liquid systems. This reaction was catalysed by lipase B from Candida antarctica (CALB) through transesterification of methyl propionate and R-2-pentanol. In the present study we show that there is no effect of the organic solvent on the enantioselectivity E of CALB for this reaction neither in the solid/gas system nor in organic liquid medium. The innovative idea of this work is the replacement of the substrates and solvent concentrations by their thermodynamic activities in order to correct the differences of substrates solvation in the different media studied and to control the level of availability of the different chemical species for the enzyme. Finally, we established that the solid/gas bioreactor is a suitable tool to study the influence of organic components on the enantioselectivity of lipases because it permits to control and adjust independently thermodynamic activities of substrates, on the one hand, and of an extra-added organic component on the other hand.
KINETIC STUDY OF PALMITIC ACID ESTERIFICATION CATALYZED BY Rhizopus oryzae RESTING CELLS
Acta Biológica Colombiana, 2009
In the present study, a kinetic model for the biocatalytic synthesis of esters using Rhizopus oryzae resting cells is proposed. The kinetic study has been made in a range of 30-50 °C and atmospheric pressure. The Influence of operating variables, water content, pH, amount of mycelium was studied. Different values of temperature, initial mycelium concentration and acid/alcohol molar ratio were tested. Initial rates were estimated from the slope of the concentration of palmitic acid, or their corresponding ester at conversions of less than 10%, versus time and reported as mmol l-1 min -1. The values of kinetic constants were computed using the freeware program SIMFIT (http:\\www.simfit.man.ac.uk). Key words: bound lipase, esterification, fungal resting cells, Rhizopus oryzae, palmitic acid, propanol. RESUMEN En el presente estudio, un modelo cinético para la síntesis de esteres usando Rhizopus oryzae resting cells es propuesto. El estudio cinético fue realizado en un rango de temperat...
Effects of methanol on lipases: Molecular, kinetic and process issues in the production of biodiesel
Biotechnology Journal, 2014
The biotechnological production of biodiesel is based on transesterification/esterification reactions between a source of fatty acids and a short-chain alcohol, usually methanol, catalysed by enzymes belonging to the class known as lipases. Several lipases used in industrial processes, although stable in the presence of other organic solvents, are inactivated by methanol at or below the concentration optimal for biodiesel production, making it necessary to use stepwise methanol feeding or pre-treatment of the enzyme. In this review article we focus on what is currently know about methanol inactivation of lipases, a phenomenon which is not common to all lipase enzymes, with the goal of improving the biocatalytic process. We suggest that different mechanisms can lead to inactivation of different lipases, in particular substrate inhibition and protein unfolding. Attempts to improve the performances of methanol sensitive lipases by mutagenesis as well as process engineering approaches are also summarized