peroxidase

Peroxidases are a broad family of enzymes that catalyze oxidation–reduction reactions in which hydrogen peroxide serves as the oxidant. Most peroxidases are heme-containing enzymes that use H2O2 to oxidize a wide range of substrates, generating water as a byproduct.

Examples include horseradish peroxidase (HRP), lactoperoxidase, myeloperoxidase, chloroperoxidase, and plant class III peroxidases. HRP is widely used in laboratory assays and serves as a model enzyme for mechanistic studies due to its robust activity and well-characterized chemistry.

Mechanistically, peroxidases typically cycle the heme iron through reactive intermediates such as Compound I and Compound II. In the catalytic cycle, hydrogen peroxide oxidizes the resting enzyme to Compound I, which then oxidizes substrates to regenerate the resting state. This redox cycle enables efficient oxidation of diverse substrates.

Peroxidases have broad substrate specificity, including phenols, anilines, and various dyes. They can catalyze polymerization, decolorization of dyes, and halogenation in the presence of halide ions. In biochemistry and diagnostics, HRP and other peroxidases are used with chromogenic substrates to produce measurable color changes in assays such as ELISA.

Applications span research, diagnostics, and industry. In medicine and diagnostics, peroxidases are employed in ELISA, Western blotting, and biosensors. In industry, they aid in pulp bleaching, textile processing, and environmental cleanup by degrading phenolic pollutants and dyes, and in biocatalysis for oxidative transformations.

Peroxidases occur in diverse organisms, with notable examples including plant extracellular class III peroxidases, mammalian myeloperoxidase, and fungal chloroperoxidase. Their structures feature a heme prosthetic group embedded in a protein matrix, enabling versatile redox chemistry.