Peroxidases or peroxide reductases ( EC numberbr>1.11.1.x
are a large group of

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

s which play a role in various biological processes. They are named after the fact that they commonly break up

peroxide In chemistry, peroxides are a group of Chemical compound, compounds with the structure , where the R's represent a radical (a portion of a complete molecule; not necessarily a free radical) and O's are single oxygen atoms. Oxygen atoms are joined ...

s, and should not be confused with other enzymes that ''produce'' peroxide, which are often oxidases.

Functionality

Peroxidases typically catalyze a reaction of the form: :ROOR' + \overset + 2H+ -> ce + R'OH

Optimal substrates

For many of these enzymes the optimal substrate is

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscosity, viscous than Properties of water, water. It is used as an oxidizer, bleaching agent, and antiseptic, usua ...

, but others are more active with organic

hydroperoxide Hydroperoxides or peroxols are Chemical compound, compounds of the form ROOH, where R stands for any group, typically Organic compound, organic, which contain the hydroperoxy functional group (). Hydroperoxide also refers to the hydroperoxide anio ...

s such as lipid peroxides. Peroxidases can contain a

heme Heme (American English), or haem (Commonwealth English, both pronounced /Help:IPA/English, hi:m/ ), is a ring-shaped iron-containing molecule that commonly serves as a Ligand (biochemistry), ligand of various proteins, more notably as a Prostheti ...

cofactor in their active sites, or alternately redox-active

cysteine Cysteine (; symbol Cys or C) is a semiessential proteinogenic amino acid with the chemical formula, formula . The thiol side chain in cysteine enables the formation of Disulfide, disulfide bonds, and often participates in enzymatic reactions as ...

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. * On the other hand, for an enzyme such as cytochrome c peroxidase, the compounds that donate electrons are very specific, due to a very narrow active site.

Classification

Protein families that serve as peroxidases include: * Haem-using ** haem peroxidase and the related animal heme-dependent peroxidases ** DyP-type peroxidase family **

Catalase Catalase is a common enzyme found in nearly all living organisms exposed to oxygen (such as bacteria, plants, and animals) which catalyzes the decomposition of hydrogen peroxide to water and oxygen. It is a very important enzyme in protecting ...

** some haloperoxidase ** Di-haem cytochrome c peroxidase * Non-heme ** Thiol: glutathione peroxidase, peroxiredoxin ** vanadium bromoperoxidase ** Alkyl hydroperoxide reductase ** Manganese peroxidase ** NADH peroxidase

Characterization

The glutathione peroxidase family consists of 8 known human isoforms. Glutathione peroxidases use glutathione as an electron donor and are active with both

and organic hydroperoxide substrates. Gpx1, Gpx2, Gpx3, and Gpx4 have been shown to be

selenium Selenium is a chemical element; it has symbol (chemistry), symbol Se and atomic number 34. It has various physical appearances, including a brick-red powder, a vitreous black solid, and a grey metallic-looking form. It seldom occurs in this elem ...

-containing enzymes, whereas Gpx6 is a selenoprotein in humans with cysteine-containing homologues in rodents.

Amyloid beta Amyloid beta (Aβ, Abeta or beta-amyloid) denotes peptides of 36–43 amino acids that are the main component of the amyloid plaques found in the brains of people with Alzheimer's disease. The peptides derive from the amyloid-beta precursor prot ...

, when bound to heme, has been shown to have peroxidase activity. A typical group of peroxidases are the haloperoxidases. This group is able to form reactive halogen species and, as a result, natural organohalogen substances. A majority of peroxidase protein sequences can be found in the PeroxiBase database.

Pathogenic resistance

While the exact mechanisms have yet to be determined, peroxidases are known to play a part in increasing a plant's defenses against pathogens. Many members of the

Solanaceae Solanaceae (), commonly known as the nightshades, is a family of flowering plants in the order Solanales. It contains approximately 2,700 species, several of which are used as agricultural crops, medicinal plants, and ornamental plants. Many me ...

, notably ''Solanum melongena'' (eggplant/aubergine) and '' Capsicum chinense'' (the habanero/Scotch bonnet varieties of chili peppers) use Guaiacol and the enzyme guaiacol peroxidase as a defense against bacterial parasites such as '' Ralstonia solanacearum'': the gene expression for this enzyme commences within minutes of bacterial attack.

Applications

Peroxidase can be used for treatment of industrial waste waters. For example,

phenols In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of one or more hydroxyl groups (− O H) bonded directly to an aromatic hydrocarbon group. The simplest is phenol, . Phenolic compounds ar ...

, 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 polymers and oligomers are produced that are less toxic than phenols. It also can be used to convert toxic materials into less harmful substances. There are many investigations about the use of peroxidase in many manufacturing processes like adhesives, computer chips, car parts, and linings of drums and cans. Other studies have shown that peroxidases may be used successfully to polymerize anilines and phenols in organic solvent matrices.Tuhela, L., G. K. Sims, and O. Tuovinen. 1989. Polymerization of substituted anilines, phenols, and heterocyclic compounds by peroxidase in organic solvents. Columbus, Ohio: The Ohio State University. 58 pages. Peroxidases are sometimes used as

histological Histology, also known as microscopic anatomy or microanatomy, is the branch of biology that studies the microscopic anatomy of biological tissue (biology), tissues. Histology is the microscopic counterpart to gross anatomy, which looks at large ...

markers. Cytochrome c peroxidase is used as a soluble, easily purified model for

cytochrome c oxidase The enzyme cytochrome c oxidase or Complex IV (was , now reclassified as a translocasEC 7.1.1.9 is a large transmembrane protein complex found in bacteria, archaea, and the mitochondria of eukaryotes. It is the last enzyme in the Cellular respir ...

References

External links

Peroxibase
a database of peroxidases {{Authority control * Hemoproteins