hemoperoxidasa

Hemoperoxidase, commonly referred to as heme peroxidase, is a family of enzymes that catalyze the oxidation of organic substrates using hydrogen peroxide as the terminal oxidant. These enzymes contain a heme prosthetic group with iron in the ferric state and are widespread in bacteria, fungi, plants, and animals. They participate in immune defense, hormone biosynthesis, pigment formation, and the breakdown of environmental compounds.

The catalytic cycle begins when the ferric enzyme reacts with hydrogen peroxide to form Compound I, a ferryl heme species with a porphyrin radical. Compound I oxidizes substrates and is reduced to Compound II, which is subsequently reduced back to the resting ferric state by a second substrate oxidation. Many peroxidases also form reactive halogen or oxo species that enable broad substrate oxidation.

Major members include mammalian myeloperoxidase (MPO) and eosinophil peroxidase (EPO); lactoperoxidase (LPO) in secretions; thyroid peroxidase (TPO) in thyroid hormone synthesis; and plant peroxidases such as classical class III enzymes, including horseradish peroxidase. Bacterial and fungal peroxidases also contribute to lignin degradation, pollutant oxidation, and microbial defense.

Biological roles vary by enzyme but commonly include microbial killing, oxidative coupling of phenolics, iodination and deiodination reactions in hormone production, and detoxification. In biotechnology, horseradish peroxidase is widely used as a reporter in immunoassays and as a biocatalyst in biosensors and bioremediation strategies.

Clinically, MPO deficiency is the most common inherited peroxidase disorder and can affect neutrophil antimicrobial activity. Peroxidases are targeted by inhibitors such as cyanide and azide in research contexts. Structural studies emphasize the conserved heme iron coordinated by histidine residues and accessory substrate channels that govern specificity.