Horseradish peroxidase heme prosthetic group

A quite different approach came from Chance and others using heme enzymes (1947). Purified horseradish peroxidase has a characteristic absorption spectrum which was visibly altered in the presence of hydrogen peroxide. When an appropriate substrate was added it was oxidized by the hydrogen peroxide and the spectrum reverted to that of the original state of the enzyme. Similar studies were performed with catalase, showing that prosthetic groups in enzymes underwent reversible changes in the course of their reactions. 

Peroxidases (E.C. 1.11.1.7) are ubiquitously found in plants, microorganisms and animals. They are either named after their sources, for example, horseradish peroxidase and lacto- or myeloperoxidase, or akin to their substrates, such as cytochrome c, chloro- or lignin peroxidases. Most of the peroxidases studied so far are heme enzymes with ferric protoporphyrin IX (protoheme) as the prosthetic group (Fig. 1). However, the active centers of some peroxidases also contain selenium (glutathione peroxidase) [7], vanadium (bromoperoxidase)... 

Colas C, Ortiz de Montellano PR (2004) Horseradish peroxidase mutants that autocataly-tically modify their prosthetic heme group. Insights into mammalian peroxidase heme-protein covalent bonds. J Biol Chem 279 24131-24140... 

Ator MA, David SK, Ortiz de Montellano PR (1987) Structure and catalytic mechanism of horseradish peroxidase. Regiospecific meso alkylation of the prosthetic heme group by alkylhydrazines. J Biol Chem 262 14954-14960... 

Myoglobin has the same prosthetic group as some peroxidases, such as horseradish peroxidase (HRP) or cytochrome c peroxidase, and reacts with H2O2 to produce a ferryl species, PFe(IV)=0, observed in the native peroxidase (see Iron Heme Proteins, Peroxidases, Catalases Catalase-peroxidases). However, the catalytic activity of myoglobin toward substrate oxidation is very low, because... 

Horseradish peroxidase (HRP) is an important peroxidase that contains heme, which is the protein active site with the resting state of the heme iron, Fe(III), as prosthetic group. It can catalyze the dependent one-electron oxidation of a great variety of substrates, and has been commonly employed to construct biosensors (Hai-Li Zhang et al. 2008). Peroxidase is the most frequently used enzyme for the construction of immunosensors. Successful immobilization of horseradish peroxidase on modified magnetic particles and their employment in the amperometric biosensors are mentioned in (Hai-Li Zhang et al. 2008 Yu et al. 2006). 

Horseradish peroxidase can be inactivated by protein as well as heme modifications. The reaction of horseradish peroxidase with phenylhydrazine is instructive in this regard (Ator and Ortiz de Montellano, 1987). Enzyme inactivation correlates well with covalent binding of 2 equivalents of radiolabeled phenylhydrazine but is associated with conversion of only a small fraction of the prosthetic group to the meso-phenyl adduct. Covalent binding of a metabolite of phenylhydrazine to the protein is therefore primarily responsible for enzyme inactivation, although the identity of the reactive species and the site at which it reacts are not known. The factors that determine whether the heme group (e.g., methylhydrazine, sodium azide) or the protein (e.g., phenylhydrazine) is the primary site of the inactivation reaction also remain elusive. 

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