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Antioxidants, nature and chemistry

 Submitted by Dr. Tamer Fouad, M.D.

Glutathione peroxidase enzyme

The glutathione redox cycle is a central mechanism for reduction of intracellular hydroperoxides. (Fig.5).

Source and Nature:

It is a tetrameric protein 85,000-D. it has 4 atoms of selenium (Se) bound as seleno-cysteine moieties that confers the catalytic activity. One of the essential requirements is glutathione as a cosubstrate.

Glutathione peroxidase reduces H2O2 to H2O by oxidizing glutathione (GSH) (Equation A). Rereduction of the oxidized form of glutathione (GSSG) is then catalysed by glutathione reductase (Equation B). These enzymes also require trace metal cofactors for maximal efficiency, including selenium for glutathione peroxidase; copper, zinc, or manganese for SOD; and iron for catalase (Halliwell, 1995).

H2O2 + 2 GSH ? GSSG + 2 H2O (equation A)

GSSG + NADPH + H+ ? 2 GSH + NADP+ (equation B)

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