Cytochrome c peroxidase (CCP) catalyses the reduction of hydrogen peroxide to water, an important step in the cellular detoxification process. Two cytochrome c molecules serve as the electron donors. Di-heme CCPs are found in bacteria including Pseudomonas aeruginosa, Paracoccus denitrificans and Pseudomonas nautica. The overall reaction is: 2 cyt c (Fe2+) + H2O2 -> 2 cyt c (Fe3+) + 2 H2O. The enzyme has two heme cofactors, referred to as high and low potential hemes (HP heme and LP heme), located in the C and N terminal domains respectively. The enzyme requires Ca2+ for activation; calcium causes structural changes and removal of a heme ligand, allowing peroxide approach.