InterPro domain: IPR010255

Peroxidases are haem-containing enzymes that use hydrogen peroxide asthe electron acceptor to catalyse a number of oxidative reactions.Most haem peroxidases follow the reaction scheme: Fe ³⁺ + H ₂ O ₂ --> [Fe ⁴⁺ =O]R' (Compound I) + H ₂ O [Fe ⁴⁺ =O]R' + substrate --> [Fe ⁴⁺ =O]R (Compound II) + oxidised substrate [Fe ⁴⁺ =O]R + substrate --> Fe ³⁺ + H ₂ O + oxidised substrate

In this mechanism, the enzyme reacts with one equivalent of H ₂ O ₂ to give [Fe ⁴⁺ =O]R' (compound I). This is a two-electron oxidation/reduction reaction where H ₂ O ₂ is reduced to water and the enzyme is oxidised. One oxidising equivalent resides on iron, giving the oxyferryl [ 1 ] intermediate, while in many peroxidases the porphyrin (R) is oxidised to the porphyrin pi-cation radical (R'). Compound I then oxidises an organic substrate to give a substrate radical [ 2 ].

Haem peroxidases include two superfamilies: one found in bacteria, fungi, plants and the second found in animals. The animal peroxidases comprise a group of homologous proteins that differ markedly from the plant/fungal/bacterial peroxidases in primary, secondary and tertiary structure, but which share with them a common function. Animal peroxidases probably arose independently of the plant/fungal/bacterial peroxidase superfamily and most likely belong to a different gene family. The crystal structures of a number of these proteins show that the active sites of animal peroxidase and plant/fungal/bacterial peroxidases are remarkably similar [ 3 ].

1. Peroxidasin: a novel enzyme-matrix protein of Drosophila development. EMBO J. 13, 3438-47
2. Structural variation in heme enzymes: a comparative analysis of peroxidase and P450 crystal structures. Structure 2, 461-4
3. Molecular evolution of thyroid peroxidase. Biochimie 81, 557-62