A peroxidase (eg. EC 1.11.1.9) is an enzyme, which may contain heme, that catalyzes a reaction of the form:
- ROOR' + electron donor (2 e-) + 2H+ → ROH + R'OH
For many of these enzymes the optimal substrate is hydrogen peroxide, but others are more active with organic hydroperoxides such as lipid peroxides.
The nature of the electron donor is very dependent on the structure of the enzyme. For example, horseradish peroxidase can use a variety of organic compounds as electron donors and acceptors. Horseradish peroxidase has a broad and accessible active site and many compounds can reach the site of the reaction. For an enzyme such as cytochrome c peroxidase, the compounds that donate electrons are very specific, because there is a very closed active site.
Peroxidases are sometimes used as histological markers. Cytochrome c peroxidase is used as a soluble, easily purified model for cytochrome c oxidase.
Glutathione peroxidase is a peroxidase found in humans, which contains selenocysteine. It uses glutathione as a electron donor and is active with both hydrogen peroxide and organic hydroperoxide substrates.
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