Glutathione peroxidase

Glutathione peroxidase is the general name of an enzyme family with peroxidase activity whose main biological role is to protect the organism from oxidative damage. The biochemical function of glutathione peroxidase is to reduce lipid hydroperoxides to their corresponding alcohols and to reduce free hydrogen peroxide to water.

Isozymes
There are several isozymes encoded by different genes, which vary in celullar location and substrate specificity. Glutathione peroxidase 1 is the most abundant version, found in the cytoplasm of nearly all mammalian tissues, whose preferred substrate is hydrogen peroxide.

Reaction
An example reaction that glutathione peroxidase catalyzes is:


 * 2GSH + H2O2 &rarr; GS–SG + 2H2O,

where GSH represents reduced monomeric glutathione, and GS–SG represents glutathione disulphide.

Glutathione reductase then reduces the oxidized glutathione to complete the cycle:


 * GS–SG + NADPH + H+ &rarr; 2 GSH + NADP+.

Structure
Glutathione peroxidase is a selenium-containing tetrameric glycoprotein, that is, a molecule with four selenocysteine amino acid residues. As the integrity of the cellular and subcellular membranes depends heavily on glutathione peroxidase, the antioxidative protective system of glutathione peroxidase itself depends heavily on the presence of selenium.

GP in other animals
Mice genetically engineered to lack glutathione peroxidase 1 (Gpx1 knockout mice) are phenotypically normal, indicating that this enzyme is not critical for life.

However, glutathione peroxidase 4 knockout (Gpx4 knockout) mice die during early embryonic development.

There is some evidence that reduced levels of glutathione peroxidase 4 can increase life expectancy in mice.

The bovine erythrocyte enzyme has a molecular weight of 84 kDa.

History
Glutathione peroxidase was discovered in 1957 by Gordon C. Mills.