Enzymes and Free Radicals

Abstract

Enzymes play an important role in formation and transformations of reactive oxygen forms. A survey of such enzymes is given with emphasis on their interrelations. The following enzymes important in the formation of free radicals or reactive oxygen or nitrogen forms are described in more detail: NADPH oxidase, myeloperoxidase, nitroxide synthase and xanthine oxidase. Superoxide dismutase, playing a central role in removal of free radicals catalyzes transformation of superoxide to hydrogen peroxide. The latter is removed in subsequent reactions, in which catalase and peroxidases as biocatalysts take part, glutathione peroxidase being of greatest significance. The above enzymes, their functions, structures and localization in the cell are treated in more detail. The states leading to their increased or decreased activities as well as the consequences of genetically caused defects in their synthesis are described.