Interaction of fungal laccases and laccase-mediator systems with lignin

The interaction between fungal laccases from Trametes basidiomycetes and different lignins has been studied using electrochemical and chromatographic methods. The kinetic parameters for the oxidation reaction of hydroquinone and for Kraft lignin by molecular oxygen catalysed by Trametes hirsuta laccase have been investigated. Polymerisation of lignin by laccase was shown. The process was independent on the source of lignin as well as on the origin and purity of the enzymes. A complex pattern of interaction between the laccase-mediator system (LMS) and lignin was shown. Along with the polymerisation of lignin, the ability to degrade lignin using the LMS was observed. Data generated by combining size exclusion chromatographic separation of lignin with the use of a laccase modified electrode as post column detector, strongly suggest that laccase can oxidise natural lignin by a long-range electron transfer mechanism. The influence of the origin of lignin as well as source of the enzyme on this process was also shown.