Lignin Peroxidase Of

Ligninase is a generic name for a group of isozymes that catalyze the oxidative depolymerization of lignin. Although undoubtedly produced by other lignin-degrading fungi, these isozymes to data have been isolated only from the basidiomycete Phanerochaete chrysosporium Burds. 1,2 These ligninases are extracellular and are produced during secondary metabolism, brought about by nutrient starvation. Nitrogen limitation is usually employed, as described here, but carbon-limited cultures have also been used for ligninase production. 3 The ligninases exhibit a high degree of homology. They are all heme-containing glycoproteins and all cross react with a polyclonal antibody raised to the predominant ligninases. 4 Since they all have overlapping substrate specificities, the exact role of this multiplicity is not yet understood. The number of genes encoding for ligninases is not yet known. The major isozyme, ligninase H8, has been extensively characterized and is the protein initially isolated by Tien and Kirk. 5 Based on kinetic 6 and spectroscopic data, 7 this ligninase has been characterized as a peroxidase containing one high-spin ferric heme per enzyme molecule. 8 Like horseradish peroxidase, the ligninases are capable of catalyzing a wide range of oneand two-electron oxidations. The substrates of ligninase, however, exhibit much higher reduction potentials. This property, along with its low pH optimum, 6 imparts ligninase with the unique ability to catalyze the oxidative depolymerization of lignin and the oxidation of methoxybenzene-containing lignin-like substrates. 9,10