Comparison of Laccases and Hemeproteins Systems in Bioremediation of Organic Pollutants

Abstract

Aim: Laccases and peroxidases have attracted great interest for industrial and environmental applications. These enzymes have a broad substrate range and a robust oxidizing ability. Moreover, using mediators or co-oxidants makes it possible to increase their catalytic activity and extend their substrate scope to more resistant chemical structures.

Background: Fungal laccases and ligninolytic peroxidases, mainly lignin and manganese peroxidases, are the privileged oxidoreductases for bioremediation processes. Nonetheless, an increasing diversity of laccases and peroxidase-type enzymes has been proposed for environmental technologies.

Objective: This article aims to provide an overview of these enzymes and compare their applicability in the degradation of organic pollutants.

Methods: Fundamental properties of the proteins are covered and applications towards polycyclic aromatic hydrocarbons (PAHs) and pesticides are specially focused.

Results: Laccases are multicopper oxidases initially studied for applications in the pulp and paper industry but able to oxidize a variety of environmentally concerning compounds. Relying on O₂, laccases do not require peroxides nor auxiliary agents, like Mn²⁺, although suitable redox mediators are needed to attack the more recalcitrant pollutants (e.g., PAHs). True and pseudo-peroxidases use a stronger oxidant (H₂O₂) and the redox chemistry at the heme site generates high potential species that allow the oxidation of dyes and some pesticides.

Conclusion: Lately, research efforts have been directed to enzyme discovery, testing with micropollutants, and improving biocatalysts' stability by immobilization and protein engineering. Further understanding of the effects of natural media components and solvents on the enzymes might lead to competitive enzymatic treatments of highly toxic media.

Keywords: Hemoglobin; dye-decolorizing peroxidases; enzyme- mediator system; halogenated pesticides; horseradish peroxidase; lignin peroxidases; organophosphorus toxicants; versatile peroxidases.