Abstract Most peroxidases use histidine as an axial ligand for heme, while chloroperoxidase (CPO) uses a thiolate, which is similar to the ligand employed by cytochrome P 450 (P 450). Several studies have also shown that, unlike other peroxidases, CPO is capable of carrying out monooxygenation reactions in a similar manner to P 450 in addition to typical peroxidase-like reactions. These observations have been attributed to the similarities of ...