peroxidases

Peroxidases are a broad group of enzymes that catalyze the reduction of peroxides, especially hydrogen peroxide, by transferring electrons from a variety of organic and inorganic substrates. They are heme-containing enzymes found in virtually all organisms, with notable representatives in plants (such as class III plant peroxidases), animals (myeloperoxidase, lactoperoxidase, and eosinophil peroxidase), fungi, and bacteria. Horseradish peroxidase (HRP) is among the best-characterized and widely used peroxidases in biochemical assays and biotechnology.

Most peroxidases operate through a two-electron oxidation of peroxide to water and generate a reactive oxidizing intermediate, commonly referred to as Compound I, a ferryl heme porphyrin radical. Compound I oxidizes substrates to form Compound II and eventually returns the enzyme to the ferric state. This cycle allows the enzyme to oxidize a broad range of substrates, including phenolics, anilines, and halides, depending on the enzyme.

In plants, class III peroxidases contribute to lignin and suberin biosynthesis and local defense reactions. In immune cells, myeloperoxidase and eosinophil peroxidase generate reactive halogen species that contribute to microbial killing.

Peroxidases are often contrasted with catalases, which primarily decompose hydrogen peroxide to water and oxygen via a different reaction pathway and are usually highly specialized for H2O2 detoxification rather than broad substrate oxidation.

Industrial and diagnostic uses include horseradish peroxidase–catalyzed colorimetric, chemiluminescent, and electrochemical detection in ELISA and Western blot assays; biocatalysis for organic synthesis; and biosensor and bioremediation applications. Activity is influenced by pH, temperature, inhibitors (e.g., cyanide, azide), and metal ions, with stability varying among peroxidases.