hemeperoksidaasit

Hemeperoksidaasit, or heme peroxidases, are a diverse family of enzymes that contain a heme prosthetic group and catalyze the reduction of peroxide substrates, typically hydrogen peroxide and organic hydroperoxides, with concomitant oxidation of various donors. They operate through a catalytic cycle that involves high-valent ferryl intermediates, commonly referred to as Compound I and Compound II, enabling two-electron and one-electron oxidation steps that propagate substrate oxidation.

Structurally, the active site centers on heme iron, usually coordinated by a proximal histidine residue. The distal pocket of the enzyme modulates the interaction with hydrogen peroxide, enabling heterolytic O–O bond cleavage and formation of reactive intermediates. The exact architecture varies among families and species, contributing to substrate specificity and reaction rates.

Heme peroxidases are widespread across life and play roles in defense, metabolism, and cell signaling. In animals, notable examples include myeloperoxidase (MPO) and eosinophil peroxidase, which participate in antimicrobial defense by generating reactive oxidants; lactoperoxidase in secretions also contributes to antimicrobial activity. Plants possess class III peroxidases involved in lignin formation, wound healing, and hormone-auxin metabolism. Fungi and bacteria contribute via lignin-degrading enzymes like lignin peroxidase and manganese peroxidase, as well as catalase-peroxidases such as KatG, which combine peroxidase and catalase activities.

Industrial and research uses include horseradish peroxidase (HRP) and lactoperoxidase as biocatalysts in assays, biosensors, and synthetic applications. Dysregulation of heme peroxidases relates to oxidative stress and inflammatory diseases in humans, making them both biologically important and of clinical interest.