Simplified kinetic modelling to understand the mechanism of tensioactive-aided degradation of paraoxon by a free or membrane-bound enzyme

Abstract

Today, the accumulation of low molecular weight contaminants such as organophosphate pesticides in the environment threatens human health and the economy. Strategies to enhance enzymatic processes, such as the addition of tensioactives to the reaction mixture, are currently being investigated. However, despite the observed increase in enzyme activity, the mechanism promoted by tensioactives on enzymes is not yet fully understood. A kinetic modelling study was carried out to understand the mechanism of paraoxon degradation enhancement in presence of two different types of tensioactives (CTAB and SDS). The chosen kinetic mechanism considers all possible interactions between the substrate, the enzyme and the tensioactive, whereby the enzyme is free in solution or immobilized on a polymeric membrane. The technique of non-linear multivariate optimisation was used to calculate the kinetic parameters.

For the free enzyme, the study enables a comparison of the effect of the two tensioactives for each reaction step, which leads to a deeper understanding of why CTAB, even though the kinetic mechanism is the same for both tensioactives, ensures better overall performance compared to SDS (yield coefficient (YC) = 3.49).

In contrast, when the enzyme is immobilized in the membrane, the kinetic mechanism in the presence of SDS differs from that in the presence of CTAB and the two tensioactives cause a similar reaction enhancement (yield coefficient (YC) ≈ 1). The interaction between the enzyme and the tensioactive is hindered when the enzyme is bound to the membrane, resulting in less effective catalytic degradation than the free enzyme.

The improvement in the enzymatic degradation of paraoxon in the presence of tensioactives can be explained by the fact that the tensioactive can bind both the enzyme and the reagent, which increases the overall reaction performance in both enzyme configurations, with the free enzyme performing better.