Glutathione-decomposing enzymes

This reaction is mediated by an enzyme called a glutathione transferase, which facilitates the encounter of GSH and the compound it is attacking (Mannervik, 1985 Vuilleumier, 1997). Formation of the GSH adduct (i.e., the compound formed when the two reactants are attached to one another) permits the attack of water on the previously chlorinated carbon and since the resulting intermediate is not particularly stable in this case, it decomposes, releasing formaldehyde and regenerating glutathione in a reaction much like the dehydration of gem-diols ... 

Free radicals participate in a wide variety of chemical reactions. The most significant radicals in the human body are the superoxide radical (O2") and the hydroxyl radical (OH ). These radicals cause the oxidative damage of biomolecules. Substances eliminating free radicals can be used to prevent these harmful processes. Free radicals can be decomposed enzymatically superoxide dismutase, glutathione peroxidase and catalase enzymes are the major players in this game. Superoxide dismutase catalyzes the following reaction ... 

Glutathione peroxidase functions the same way to decompose the hydrogen peroxide into water and oxygen but in addition destroys hydroperoxides by another, non-radical mechanism. Hydrogen peroxide is dangerous because in the presence of the transition metals (e.g. it can be the source of the OH radical. Vitamin E (alfa-tocopherol) supposedly intercepts the peroxide radicals RCK), appears at the peroxide oxidation of lipids, transfers than into hydroperoxides ROOH and the vitamin C (ascorbic acid) reactivates alfa-tocopherol. It is at the same time a co-factor of peroxidase (an enzyme ascorbate... 

Hydroperoxides (ROOH) can be decomposed by enzymes called peroxidases. Most of peroxidases are dependent on iron as catalyst, but a few of them use manganese. A very interesting peroxidase, called glutathione peroxidase, uses selenium as its catalytic element. Selenium is one of the most toxic elements, but a very small quantity of it is required by almost all organisms. It is used for glutathione peroxide as well as a few other enzymes. This enzyme is much more efficient in destroying certain types of hydroperoxides than the other more common iron-dependent peroxidases. 

An enzyme that requires selenium specifically is glutathione peroxidase (GPO). This enzyme decomposes very efficiently one of the so-called active oxygen species, i.e., hydroperoxide. Accumulation of hydroperoxides in cell membranes is believed to be one of the causes of aging. GPO thus helps prolonging life. 

Many foods also contain glutathione peroxidase. Glutathione peroxidase differs from catalase in that it decomposes both lipid and hydrogen peroxides. GSH-Px is a selenium-containing enzyme that catalyzes hydrogen or lipid (LOOK) peroxide reduction using reduced glutathione (GSH) ... 

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