Glutathione peroxidase 3 (GPx-3), also known as plasma glutathione peroxidase (GPx-P) or extracellular glutathione peroxidase is an
enzyme
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...
that in humans is encoded by the ''GPX3''
gene
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
.
GPx-3 belongs to the
glutathione peroxidase
Glutathione peroxidase (GPx) () 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 h ...
family, which functions in the detoxification of hydrogen peroxide. It contains a
selenocysteine
Selenocysteine (symbol Sec or U, in older publications also as Se-Cys) is the 21st proteinogenic amino acid. Selenoproteins contain selenocysteine residues. Selenocysteine is an analogue of the more common cysteine with selenium in place of the s ...
(Sec) residue at its active site. The selenocysteine is encoded by the UGA codon, which normally signals translation termination. The 3' UTR of Sec-containing genes have a common stem-loop structure, the sec insertion sequence (SECIS), which is necessary for the recognition of UGA as a Sec codon rather than as a stop signal.
Thiol specificity
GPx-3 has a wide thiol specificity. The sources of reducing power for GPx-3 in vitro include GSH, cysteine, mercaptoethanol, and dithiothreitol. There is an evidence of effectiveness of homocysteine in reduction of GPx-3: GSH can be completely replaced by reduced homocysteine in vitro.
Changes during ontogeny
In the rat blood plasma, the GPx-3 activity is low during the first two weeks after birth and rapidly increasing during transition from milk nutrition to solid food. Aging is accompanied by decrease in GPx-3 activity: in the blood plasma of rats it occurs around 23-26 months of age.
References
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External links
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EC 1.11.1
Antioxidants
Selenoproteins
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