Dehydrogenations and Hydroxylations Catalyzed by Peroxidases

Peroxidases catalyze the reaction of substrates with hydrogen peroxide. Most of the plant peroxidases, e.g., the well-investigated peroxidase of horseradish, contain ferriprotoporphyrin IX (hemin, D 10.1) as coenzyme. The prosthetic groups of the animal peroxidases are similar. Up to now only one peroxidase is known whose prosthetic group has a fundamentally different structure, a flavin enzyme from Streptococcus faecalis. 

The peroxidases first break down hydrogen peroxide to form hydroxyl radicals. Then they cleave either two hydrogen radicals from the substrate  

The substrate radicals formed as intermediates during the first reaction may react spontaneously with each other or with other compounds. Hence similar products are found after the action of laccases (C 2.3.1) and peroxidases on phenols. 

The peroxidase-catalyzed polymerizations of phenols involve the formation of phenoxy radicals as an initial step. These radicals may either condense with each other or may be added to unsaturated compounds forming irregular high molecular polymers (see the biosynthesis of lignin, D 22.2.3). 

) The Enzymes, Vol. 13, Dehydrogenases, Oxidases, Hydrogen Peroxide Cleavage. Academic Press, New York 1977 

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