Lignases

Lignases are a group of oxidative enzymes capable of degrading lignin, the heterogeneous, non-carbohydrate polymer that strengthens plant cell walls. They are produced by white-rot fungi, some bacteria, and, in limited cases, actinomycetes. The term "lignases" is used in older or broader contexts to describe enzymes that catalyze lignin depolymerization, rather than a single enzyme family.

Major lignin-degrading enzymes include lignin peroxidase, manganese peroxidase, and versatile peroxidase (all class II peroxidases) as well as laccase, a multicopper oxidase. LiP can oxidize non-phenolic lignin linkages directly using high redox potential and hydrogen peroxide. MnP oxidizes Mn2+ to Mn3+, which diffuses and oxidizes phenolic structures. VP combines features of LiP and MnP. Laccases oxidize phenolic units using molecular oxygen, and, with redox mediators, can extend activity to non-phenolic lignin moieties. These enzymes often operate together in synergistic systems within fungal secretomes.

Ecologically, lignases contribute to carbon cycling by mediating lignin turnover in forest soils and decaying wood. They are influenced by pH, redox conditions, and the presence of mediators or oxidants. Industrial interest focuses on biopulping and biobleaching of kraft pulp, pretreatment of lignocellulosic biomass for biofuel production, and environmental remediation of persistent pollutants through lignin-like structures.