4.09 – Peroxidases*

The human peroxidases are hemoproteins that utilize H2O2 to oxidize a variety of endogenous and exogenous substrates. The well-established members of this enzyme family are eosinophil peroxidase, lactoperoxidase, myeloperoxidase, and thyroid peroxidase. The reactions catalyzed by these enzymes, which include halide oxidation and substrate free radical formation, contribute to cellular pathology and xenobiotic toxicity. In contrast to the peroxidases, the peroxiredoxins are cysteine-containing proteins that detoxify both H2O2 and alkyl peroxides at the expense of electron donors such as thioredoxin and cellular thiols. They do not oxidize other endogenous or xenobiotic substrates. The peroxiredoxins appear to be constituents of oxidative stress signaling pathways and help to ameliorate oxidative stress, but do not appear to contribute significantly to xenobiotic toxicity.