Catalytic structure–function relationships in heme peroxidases

This chapter reviews catalytic structure–function relationships in heme peroxidases. One advantage of structure–function studies on heme proteins and heme enzymes is that the relatively rigid heme provides a well-defined active-site cavity. Many heme proteins with diverse functions share the same heme prosthetic group, which necessitates that the biological activity be governed by the polypeptide. Peroxidases catalyze the oxidation of a wide variety of organic and inorganic substrates by hydrogen peroxide. The chapter describes heme peroxidases of known structure and enzyme intermediates formed during their catalysis. Catalases react by a mechanism similar to that of peroxidases but the reaction catalyzed is the disproportionation of peroxide. The biological function of catalases appears to be the prevention of peroxide buildup, but peroxidases have a variety of roles, including biosynthesis and defense. A number of heme peroxidases defend organisms against infection. Neutrophils that are specialized white blood cells playing a key role in combating infection contain high peroxidase activity. The plant peroxidase superfamily consists of evolutionarily related heme peroxidases from bacteria, fungi, and plants.