Peroxidasetype

Peroxidase-type enzymes, commonly referred to as peroxidases, form a diverse family of heme-containing enzymes that catalyze the reduction of peroxides, most notably hydrogen peroxide, using various electron donors. They are widely distributed among bacteria, archaea, fungi, plants, and animals and participate in processes ranging from microbial defense and oxidative stress response to cell wall formation and hormone signaling.

Most peroxidases contain a heme cofactor at the active site and operate via a characteristic two-stage catalytic cycle. In the first stage, hydrogen peroxide oxidizes the resting ferric heme to compound I, a ferryl-porphyrin species with a radical character. In subsequent steps, compound I is reduced back to ferric state by one- or two-electron transfer from substrate molecules, which are oxidized in the process. The overall reaction involves reducing peroxide to water while transferring electrons from donors such as phenolic compounds, thiols, or other organic substrates.

Classification is often contextual by organism and localization. Plant peroxidases include secreted class III enzymes involved in lignin formation and defense. Animal peroxidases include myeloperoxidase, lactoperoxidase, and eosinophil peroxidase, which generate reactive species for antimicrobial defense. Bacterial and fungal peroxidases also contribute to oxidative stress resistance and metabolic processes. Some peroxidases are extracellular or cell-wall associated, while others are intracellular.

Applications of peroxidases are widespread in research and industry. Horseradish peroxidase, for example, is a staple in diagnostic assays and histochemistry due to its robust activity and easy coupling to substrates. Peroxidase activity assays also serve in clinical diagnostics, environmental monitoring, and biosensor development.