Peroxidases: past and present

The history of peroxidases spans nearly two centuries. Our knowledge has developed from early phenomenological observations of the colored products of peroxidase-catalyzed reactions, to our present understanding of many of the steps in the complex peroxidation reaction mechanism. Peroxidases are ubiquitous in plant and animal tissues and occur in diverse structural forms. Collectively, they are able to catalyze the hydroperoxide oxidation of many different kinds of organic and inorganic compounds. In spite of the great diversity of structures and functions, mechanisms of heme-containing peroxidases have several common features: (i) the transfer of the oxidizing equivalents of the hydroperoxidase to the enzyme to form Compound I, (ii) the reduction of Compound I by the transfer of electrons from donor molecules, (iii) the inactivation of Compound I by excess hydroperoxide. Rate constants for these and other steps in the peroxidation mechanism, as well as redox potentials, have been reported for many peroxidases. The molecular basis for the donor specificity of peroxidases has not yet been elucidated. Today, much interest is directed towards the biological functions of peroxidases and their reaction products.