Antioxidant defences

The enzyme superoxide dismutase decomposes superoxide radicals by converting them to hydrogen peroxide plus oxygen. Catalase and glutathione (GSH) peroxidase are enzymes that decompose peroxides, particularly hydrogen peroxide.

Catalase

Glutathione peroxidase

(oxidized glutathione)

There are two forms of superoxide dismutase: a mitochondrial enzyme, which contains manganese, and a cytosolic enzyme, which contains copper and zinc. Catalase contains iron, while glutathione peroxidase contains selenium. These metal ions must come from the diet. At least some of the effects that selenium, copper, zinc, iron and glutathione have on immune function relate to their roles in antioxidant defence (see Grimble, Chapter 7, Prasad, Chapter 10, Kuvibidila and Baliga, Chapter 11, and McKenzie et al., Chapter 12, this volume). The diet also provides many other, non-enzymic, components of the body's antioxidant defence system. These include the antioxidants vitamins C and E and the carotenoids.

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