Haem peroxidases (or heme peroxidases) are haem-containing enzymes that use hydrogen peroxide as the electron acceptor to catalyse a number of oxidative reactions.
Most haem peroxidases follow the reaction scheme: In this mechanism, the enzyme reacts with one equivalent of H2O2 to give [Fe4+=O]R' (compound I).
This is a two-electron oxidation/reduction reaction in which H2O2 is reduced to water, and the enzyme is oxidized.
One oxidizing equivalent resides on iron, giving the oxyferryl[1] intermediate, and in many peroxidases the porphyrin (R) is oxidized to the porphyrin pi-cation radical (R').
The first one can be viewed as consisting of 3 major classes:[3] The crystal structures of a number of these proteins show that they share the same architecture - two all-alpha domains between which the haem group is embedded.