Mechanism and Role of Covalent Heme Binding in the CYP4 Family of P450 Enzymes and the Mammalian Peroxidases

The CYP4 family of cytochrome P450 enzymes and the mammalian peroxidases covalently bind their heme groups. In the CYP4 enzymes this involves one, and in the peroxidases two, covalent ester links between heme methys and carboxylic acid side-chains. In addition, in myeloperoxidase, a methionine forms a sulfonium link to a heme vinyl group. The ester links in both classes of proteins are autocatalytically formed. One role of the covalent bonds in peroxidases is to protect the heme group from modification by catalytically generated reactive products. The covalent heme bond in CYP4 enzymes contributes to their high preference for omega- over (omega-1)-hydroxylation.