Simplified Kinetic Modelling to Understand the Mechanism of Surfactant-Aided Degradation of Paraoxon by a Free or Membrane-Bound Enzyme

Abstract

Today, the accumulation of low molecular weight contaminants in the environment threatens human health and the economy. The immobilisation of enzymes capable of degrading organophosphates on membranes, enables the development of biocatalytic membranes that can treat polluted water. The conversion of the pesticide paraoxon by free and immobilised phosphotriesterase is enhanced by surfactants. A kinetic modelling study was carried out to understand the process with two different surfactants. The kinetic mechanism considers all possible interactions between the substrate, the enzyme and the surfactant, whereby the enzyme is free in solution or immobilised on a polymeric membrane. The technique of non-linear multivariate optimisation was used. For the free enzyme, the results revealed that the kinetic mechanism is the same in the presence of SDS or CTAB; however, CTAB causes a much stronger reaction enhancement than SDS.  In contrast, when the enzyme is immobilised in the membrane, the kinetic mechanism in the presence of SDS differs from that in the presence of CTAB and the two surfactants cause a similar reaction enhancement.  The improvement in the enzymatic degradation of paraoxon in the presence of surfactants can be explained by the fact that the surfactant can bind both the enzyme and the reagent.

Keywords: Enzyme, membrane, immobilized enzyme, micropollutant, surfactant, kinetic mechanism.