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:Fe3+ + H2O2 [Fe4+=O]R' (Compound I) + H2O[Fe4+=O]R' + substrate → [Fe4+=O]R (Compound II) + oxidized substrate[Fe4+=O]R + substrate → Fe3+ + H2O + oxidized substrate