Phenol Oxidases (Laccases) (Benzenediol or P-Diphenol: Oxygen Oxidoreductases, EC 22.214.171.124)
Laccases are glycosylated blue multi-copper oxidoreductases (BMCO) with at least four copper atoms and use oxygen molecule for oxidizing several aromatic and nonaromatic compounds via radical-catalyzed reaction mechanism (Claus 2004; Baldrian 2006). Reaction mechanism includes redox reaction, reduction of molecular oxygen into two molecules of water and oxidation of substrate, such as aromatic compounds, arylamines, anilines, thiols, and lignins (Thurston 1994).
Laccases were first discovered in 1883 in the latex of Rhus vernicifera, a Japanese lacquer tree (Yoshida 1883). Laccases were identified in higher plants, insects, few bacteria, and several fungi (Claus 2004). Laccases are mostly found in white-rot fungi, particularly Lentinus tigrinus (Ferraroni et al. 2007), Cerrena unicolor strain 137 (Michniewicz et al. 2006), T. versicolor (Necochea et al. 2005), Trametes sp. strain AH28-2 (Xiao et al. 2003), Trametes pubescens (Shleev et al. 2007), and Cyathus bulleri (Salony et al. 2006). It has been shown that laccase can be produced in brown-rot fungi, Coniophora puteana, such as using submerged culture (Lee et al. 2004). Laccases are also produced by ascomycetes, such as Melanocarpus albomyces (Hakulinen et al. 2006), Magnaporthe grisea (Iyer and Chattoo 2003), Myrothecium verrucaria 24G-4 (Sulistyaningdyah et al. 2004), and Neurospora crassa (Germann et al. 1988). The presence of laccase was also found in deutero- mycetes, especially Botrytis cinerea and Myceliophthora thermophila (Marbach et al. 1983). In addition to fungi, laccases are also produced by some bacteria such as Bacillus subtilis (Martins et al. 2002) and Bacillus licheniformis (Koschorreck et al. 2008).