Modelling the transient kinetics of laccase-catalyzed oxidation of four aqueous phenolic substrates at low concentrations

Laccase-Catalyzed Oxidation of Mixed Aqueous Phenolic Substrates at Low Concentrations

“…One approach to evaluating the feasibility of using enzymes to oxidize various contaminants at realistic wastewater concentrations was reported recently [5,6]. Specifically, a model was developed that accurately predicted the transient kinetics of the laccase-catalyzed oxidation of aqueous phenolic substrates at concentrations in the micromolar to sub-micromolar range [5,6]. This model was designed to predict the time course of the enzymatic oxidation of a substrate while accounting for the effects of unproductive side reactions and enzyme inactivation.…”

“…When the model was applied to four different substrates, including phenol (P), 4-cumylphenol (CP), triclosan (TCL), and estradiol (E2), predictions of substrate concentration as a function of time proved to be very accurate over several orders of magnitude of substrate and laccase concentrations and over prolonged reaction periods. The model was then used to demonstrate that substantial conversion (i.e., 90% to 99.9%) of estradiol, cumylphenol, and triclosan could be achieved for initial substrate concentrations in the micromolar and sub-micromolar range using pragmatic reaction times and laccase concentrations [5,6]. This is in contrast to phenol, a slow substrate of laccase, which was shown not to be practically amenable to substantial oxidation in the same concentration range [5].…”

“…An important drawback of this model, however, is that it does not account for the possibility that more than one substrate may be present in a reacting mixture. This could be of particular importance for applications where one may wish to selectively target the oxidation of certain aqueous pollutants that, due to their particularly problematic nature, represent important hazards even when they are present at very low concentrations [5,6]. For example, even when in nanomolar concentrations in surface waters, the estrogenic properties of estradiol can have important impacts on fish species [7,8].…”

“…Alternatively, a fast secondary substrate could be preferentially oxidized by the enzyme, resulting in a sequential delay in the oxidation of the slower target substrate until most of the secondary substrate is depleted. Secondly, given that different substrates can cause very different rates of inactivation of the enzyme [5,6], the presence of a secondary substrate that inactivates laccase during its oxidation could gradually cause a decrease in the rate of oxidation of the target substrate over time. Inactivation during the reaction of mixed substrates could conceivably be manifested in an additive manner, where the observed rate of inactivation would simply be the sum of the rates of inactivation arising from the oxidation of individual substrates.…”

“…Four substrates of laccase were selected for the purposes of this study, namely, 17β-estradiol (estradiol), 4-cumylphenol (cumylphenol), triclosan, and phenol. Each of these substrates represent diverse groups of contaminants of environmental importance and were the subjects of earlier studies of laccase-catalyzed oxidation where, as described above, their oxidation kinetics were successfully modeled over a wide range of substrate and enzyme concentrations [5,6].…”