Peroxidase

Peroxidases (EC number [http://www.chem.qmul.ac.uk/iubmb/enzyme/EC1/11/1/ 1.11.1.x] ) are a large family of enzymes. A majority of peroxidase protein sequences can be found in the PeroxiBase database. Peroxidases typically catalyze 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. Peroxidases can contain a heme cofactor in their active sites, or redox-active cysteine or selenocysteine residues.

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 an 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.

While the exact mechanisms have yet to be elucidated, peroxidases are known to play a part in increasing a plant's defenses against pathogens. [cite journal
author = Karthikeyan M et al
title = Induction of resistance in host against the infection of leaf blight pathogen (Alternaria palandui) in onion (Allium cepa var aggregatum).
journal = Indian J Biochem Biophys
volume = 42
issue = 6
pages = 371–7
date = 2005 Dec
pmid = 16955738
format = ] Peroxidases are sometimes used as histological marker. 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 an electron donor and is active with both hydrogen peroxide and organic hydroperoxide substrates.

Amyloid beta, when bound to heme has been shown to have peroxidase activity. [cite journal
title = Amyloid-{beta} peptide binds with heme to form a peroxidase: Relationship to thecytopathologies of Alzheimer's disease | author = Hani Atamna, Kathleen Boyle | date = 21 Feb 2006 | journal = Proceedings of the National Academy of Science | volume = 103 | issue = 9 | pages = 3381 - 3386 | doi = 10.1073/pnas.0600134103]

A typical group of peroxidases are the haloperoxidases. This group is able to form reactive halogen species and as a result natural organohalogen substances.

Applications

Peroxidase can be used for treatment of industrial waste waters. For example, phenols, which are important pollutants, can be removed by enzyme-catalyzed polymerization using horseradish peroxidase. Thus phenols are oxidized to phenoxy radicals which participate in reactions where are produced polymers and oligomers that are less toxic than phenols.

Furhermore, peroxidases can be an alternative option of a number of harsh chemicals, eliminating harsh reaction conditions. There are a lot of investigations about the use of peroxidase in many manufacturing processes like adhesives, computer chips, car parts, and linings of drums and cans.

ee also

* Haloperoxidase
* Myeloperoxidase (MPO)
* Catalase
* Hemoprotein
* Peroxide
* Peroxiredoxin
* Animal heme-dependent peroxidases
* Thyroid peroxidase

References