In the present review several aspects of the lignin biodegradation process are updated, with special emphasis on three concepts: a) the multienzymatic nature of lignin attack, b) the importance of aromatic metabolites synthesized by fungi, and c) the compartimentalization of the biodegradation process. In relation to the first point, it is necessary to consider, together with the peroxidases oxidizing the lignin polymer, the enzymes reducing the radicals released during degradation (preventing repolymerization), and the enzymatic systems generating hydrogen peroxide. Secondly, some aromatic compounds synthesized by fungi play an important role in degradation, acting as intermediates in oxidation reactions and allowing the catalytic cycle of the ligninolytic peroxidases to be completed when they oxidize high redox-potential compounds. Finally, the effective degradation of lignin by fungi seems the result of the joint action of intracellular and extracellular enzymes, some of them being immobilized in the polysaccharide sheath surrounding the mycelium.

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