Abstract
The human heme peroxidase family includes myeloperoxidase (MPO), eosinophil peroxidase (EPO), lactoperoxidase (LPO), peroxidasin (Pxdn), and thyroid peroxidase (TPO). These peroxidases use H₂O₂ to oxidize a variety of endogenous and exogenous substrates. They oxidize halide ions to hypohalous acids. For MPO, LPO, and EPO, these oxidants are important for antimicrobial defense but can also cause tissue injury in inflammation. TPO is required for thyroid hormone formation and Pxdn forms a specific cross-link in collagen IV. These heme peroxidases oxidize a wide range of drugs and xenobiotics to free radicals and contribute to adverse drug reactions and xenobiotic toxicity. The peroxiredoxins are cysteine peroxidases that detoxicate H₂O₂ and alkyl peroxides at the expense of electron donors such as thioredoxin and cellular thiols. They are not known to oxidize other endogenous or xenobiotic substrates. The peroxiredoxins regulate signaling pathways and help to protect against oxidative stress but do not promote xenobiotic toxicity.