Chloroperoxidase

Chloroperoxidase is a heme-containing enzyme that catalyzes halogenation reactions using hydrogen peroxide and halide ions. It belongs to the class of haloperoxidases and was originally isolated from the soil mold Caldariomyces fumago, where it is secreted into the culture medium.

The active site contains a heme prosthetic group with a cysteine thiolate as the proximal ligand, a feature that distinguishes it from classical peroxidases. In catalysis, hydrogen peroxide oxidizes the ferric heme to Compound I, a powerful oxidant. The halide ion (chloride, bromide or iodide) is then converted by Compound I into a hypohalous acid (HOCl, HOBr or HOI), which halogenates substrates through electrophilic attack. The enzyme thus enables chlorination or bromination under mild, aqueous conditions.

CPO can halogenate a broad range of substrates, including activated aromatics such as phenols and anisoles, as well as certain aliphatic compounds and even amino acid residues in peptides. In synthetic chemistry and biocatalysis, it is valued for providing regioselective halogenation under mild conditions, often under ambient temperatures and neutral pH.

Operational aspects: CPO activity depends on proper handling of hydrogen peroxide and halide sources; excessive peroxide can inactivate the enzyme. It has been studied for applications in organic synthesis, medicinal chemistry, and environmental processes, where enzymatic halogenation offers a greener alternative to conventional chemical methods.