Laccases

Laccases are multicopper oxidase enzymes (EC 1.10.3.2) that catalyze the one-electron oxidation of a broad range of phenolic and some non-phenolic substrates, using molecular oxygen as the terminal electron acceptor and producing water. They are characterized by a catalytic site containing four copper ions distributed among a type 1 (T1) copper center and a trinuclear cluster formed by one type 2 (T2) and two type 3 (T3) copper ions. The T1 site accepts electrons from the substrate and transfers them to the trinuclear center, where O2 is reduced to water.

Laccases are produced by a variety of organisms, but are especially abundant and extracellular in basidiomycete white-rot fungi such as Trametes, Pleurotus and Pycnoporus species. They are glycoproteins with molecular masses typically in the 50–80 kDa range. The redox potential of the T1 copper can vary among laccases, influencing substrate range and activity.

The substrate scope includes phenols, anilines, and polycyclic aromatic compounds; high-redox-potential substrates often require redox mediators (mediators such as ABTS or violuric acid) to extend oxidation beyond directly accessible substrates. Laccases operate under relatively mild conditions and use O2, making them attractive for biotechnological applications. pH optima and stability are substrate-dependent and typically acidic for phenolics.

Applications of laccases include lignin degradation and pulp bleaching in the paper industry, dye decolorization and bioremediation of environmental pollutants, enzymatic synthesis and polymerization of phenolic compounds, and use in biosensors and biofuel cells. Research continues to explore diverse sources, mediator systems, and enzyme engineering to broaden substrate range and operational conditions.