In enzymology, a manganese peroxidase () is an enzyme that catalyzes the chemical reaction 2 Mn(II) + 2 H+ + H2O2 2 Mn(III) + 2 H2O The 3 substrates of this enzyme are Mn(II), H+, and H2O2, whereas its two products are Mn(III) and H2O. This enzyme belongs to the family of oxidoreductases, to be specific those acting on a peroxide as acceptor (peroxidases). The systematic name of this enzyme class is Mn(II):hydrogen-peroxide oxidoreductase. Other names in common use include peroxidase-M2, and Mn-dependent (NADH-oxidizing) peroxidase. It employs one cofactor, heme. This enzyme needs Ca2+ for activity. White rot fungi secrete this enzyme to aid lignin degradation. Discovery and characterization Manganese peroxidase (commonly referred to as MnP) was discovered in 1985 simultaneously by the research groups of Michael H. Gold and Ronald Crawford in the fungus Phanerochaete chrysosporium. The protein was genetically sequenced in P. chrysoporium in 1989. The enzyme is thought to be unique to Basidiomycota as no bacterium, yeast, or mold species has yet been found which naturally produces it. Reaction mechanism MnP catalysis occurs in a series of irreversible oxidation-reduction (redox) reactions which follow a ping-pong mechanism with second order kinetics. In the first step of the catalytic cycle, H2O2, or an organic peroxide, enters the active site of MnP. There the oxygen in H2O2 binds to an Fe(III) ion in the heme cofactor to form an iron peroxide complex. Two electrons are transferred from Fe3+ to peroxide, breaking the oxygen-peroxide bond to form H2O and a Fe(IV) oxo-porphyrin radical complex. This oxidized intermediate is known as MnP Compound I. MnP Compound I then binds to a monochelated Mn(II) ion, which donates an electron to quench the radical and form Mn(III) and MnP Compound II, a Fe(IV) oxo-porphyrin complex. MnP Compound II oxidizes another Mn(II) ion to Mn(III) and is reduced by the reaction of two H+ ions and the iron bound oxygen. This reforms the Fe(III) ion in the heme and releases a second water molecule. There are many deviations from this traditional catalytic cycle. MnP Compound I can be used to oxidize free Mn(II), ferrocyanide, as well as phenolics, and other aromatic compounds. Chelators Mn(III) is unstable in aqueous media, therefore MnP releases it as a Mn(III)-carboxylic acid chelate. There are a variety of carboxylic acid chelators including oxalate, malonate, tartrate, and lactate, however oxalate is the most common. The peroxidase structure favors Mn(III)-chelates over free