Horseradish peroxidase (HRP) (HRP)

Horseradish peroxidase (HRP) is a 44 kDa heme-containing glycoenzyme primarily isolated from the roots of the horseradish plant, Armoracia rusticana (UniProt: P00433). It belongs to the Class III plant peroxidase family and utilizes a heme prosthetic group (iron protoporphyrin IX) to catalyze the oxidation of various organic and inorganic substrates using hydrogen peroxide as an electron acceptor (Veitch, 2004). In analytical assay contexts, the HRP heme site can interact with the superoxide anion (O2.-), leading to the formation of an oxy-ferrous intermediate known as Compound III, which can serve as a signal for superoxide detection or act as an interference in other ROS-based assays (Kettle et al., 1988). While HRP is not a therapeutic target in human medicine, it is a fundamental tool in clinical diagnostics, widely employed in Enzyme-Linked Immunosorbent Assays (ELISA) and immunohistochemistry to amplify signals for the detection of disease-related biomarkers. The enzyme's high turnover rate, stability, and ease of conjugation with antibodies make it a cornerstone of modern biotechnology and clinical biochemistry.

Other names

Armoracia rusticana peroxidaseHRP-CDonor:hydrogen-peroxide oxidoreductaseHorseradish peroxidase isoenzyme C

The enzyme follows a multi-step catalytic cycle where the ferric heme [Fe(III)] is oxidized by hydrogen peroxide to form a high-valent oxo-ferryl intermediate (Compound I), which is then reduced back to the resting state via two successive one-electron transfers from substrates, passing through a second intermediate (Compound II). In the presence of superoxide, the heme iron can form an oxy-ferrous complex (Compound III), which is catalytically distinct from the standard peroxidase cycle.