Kinetics and physico-chemical properties of white-rot fungal laccases

[摘要] Laccase (EC 1.10.3.2, p-diphenol oxidase) is one of a few enzymes that have beenstudied since the nineteenth century. Yoshida first described laccase in 1883 when heextracted it from the exudates of the Japanese lacquer tree, Rhus vernicifera.(Thurston, 1994; Levine, 1965). In 1896 laccase was demonstrated to be a fungalenzyme for the first time by both Bertrand and Laborde (Thurston, 1994; Levine,1965). Laccase is a member of the large blue copper proteins or blue copper oxidases,which comprise a small group of enzymes. Other enzymes in this group are the plantascorbate oxidases and the mammalian plasma protein ceruloplasmin (Thurston,1994; Xu, 1996; Ducros et al., 1998).Laccases are either mono or multimeric copper-containing oxidases that catalyse theone-electron oxidation of a vast amount of phenolic substrates. Molecular oxygenserves as the terminal electron acceptor and is thus reduced to two molecules of water(Ducros et al., 1998). The ability of laccases to oxidise phenolic compounds as wellas their ability to reduce molecular oxygen to water has lead to intensive studies ofthese enzymes (Jolivalt et al., 1999; Xu, 1996; Thurston, 1994). The biotechnologicalimportance of these enzymes can also be attributed to their substantial retention ofactivity in organic solvents with applications in organic synthesis.Laccases have widespread applications, ranging from effluent decolouration anddetoxification to pulp bleaching, removal of phenolics from wines and dye transferblocking functions in detergents and washing powders, many of which have beenpatented (Yaver et al., 2001). The biotechnological application of laccase has beenexpanded by the introduction of laccase- mediator systems, which are able to oxidisenon-phenolic compounds that are otherwise not attacked and are thus able to degradelignin in kraft pulps (Bourbonnais and Paice, 1990).

[发布机构] University of the Free State