Lignin is a cell wall polymer that provides rigidity, cell adhesion, andmicrobial resistance to vascular plants. A sort of natural plastic, lignin contains more than 13 different randomly arranged chemical linkages and is responsible for sequestering roughly 25 % of the world's terrestrial biomass. The resulting heterogeneous three-dimensional matrix is resistant to enzymatic hydrolysis and is chemically stable under most environmental conditions. White-rot fungi are the only organisms capable of completely degrading the lignin polymer, and manganese peroxidase is a key enzyme in this process. It is the only enzyme known that selectively binds Mn2+, oxidizes it and releases Mn3+. In this work, the unique Mn- binding site of the enzyme was probed by site-directed mutagenesis.