Peroxidase

Peroxidases are enzymes that (usually hydrogen peroxide) to catalyze the reduction of peroxides. The reaction is mainly used for removal of toxic peroxides, as well for the oxidation of iodide in the synthesis of thyroid hormone thyroxine in human. The reverse reaction of the catalase is used in the other hand, some peroxidases of generating hydrogen peroxide. Peroxidases are found in all living things, humans 17 such enzymes have been discovered, of which five hereditary enzyme deficiency diseases are known ( DUOX2, MPO, TPO, EPX, CAT).

The reducing agents used different electron donors (in brackets added ), after which the further classification is: catalase ( a second molecule of hydrogen peroxide), cytochrome c peroxidase (reduced cytochrome c ), thyroid peroxidase ( iodide), glutathione peroxidase ( glutathione), the only plants occurring ascorbate peroxidase and manganese peroxidase occurring in fungi ( manganese (II)) and ligninase (lignin -degrading enzyme ).

Hydrogen peroxide is produced, the reduction of oxygen with NADPH ( dual oxidase) is on the one hand, the inversion of the Katalasefunktion the other hand, used.

Catalyzed reactions

The substrate specificity of peroxidases is very different. For example, in the cytochrome -c- peroxidase, the substances, which transfer the electrons, very specific. Horseradish peroxidase (English horseradish peroxidase, HRP ), however, may use a variety of donors and acceptors. Therefore, HRP is used as a marker enzyme for certain techniques of molecular biology for the detection of proteins and nucleic acids ( for example, Western blotting, Southern blotting ). Peroxidases are used as histological markers - see immunohistochemistry.

Many peroxidases possess a heme prosthetic group. But there are also other prosthetic groups, such as selenocysteine ​​in the glutathione peroxidase. This enzyme is part of the antioxidant defense system of the human organism.

Function in man

In peroxisomes caused by peroxisomal oxidases constantly H2O2, which must be eliminated as quickly cytotoxin (RH2 O2 → R H2O2). This solve peroxidases, in which they further ( detoxifying ) oxidation with H2O2 as an electron acceptor to catalyze (RH2 H2O2 → R 2 H2O). A special case is the catalase ( peroxidase ), which catalyzes two H2O2 to two H20 and O2.