A tripeptide of glycine, l-cysteine, and l-glutamate, with l-glutamate having an isopeptide bond with the amino moiety of l-cysteine. G. has a wide variety of roles in a cell; it is the most prevalent non-protein thiol. G. disulfide (GSSG) consists of two glutathiones linked via a disulfide bridge; the term oxidized g. for GSSG should be avoided since it includes the sulfones and sulfoxides. The term reduced g. is not necessary since g. is the thiol form. A deficiency of g. can cause hemolysis with oxidative stress. It is also used in the course of intermediary metabolism as a donor of thiol (SH) groups and is essential for detoxification of acetaminophen. SEE ALSO: oxidized g., reduced g., g. reductase.
- oxidized g. 1. g. acting in cells as a hydrogen acceptor; reduced by g. reductase; g. disulfide; 2. sulfones or sulfoxides of g. or g. disulfide.
- g. peroxidase an enzyme that catalyzes the reaction of two glutathiones with H2O2 forming GSSG and two water molecules; a crucial enzyme in hydrogen peroxide detoxification.
- reduced g. g. acting as a hydrogen donor; g..
- g. reductase an enzyme that catalyzes the reaction of GSSG with NADH (or NADPH) forming two glutathiones and NAD+ (or NADP+); involved in many redox reactions; a deficiency can cause hemolysis with oxidative stress.
- g. synthetase an enzyme that catalyzes the formation of g., ADP, and orthophosphate from γ-glutamylcysteine, ATP, and glycine; a deficiency will lead to metabolic acidosis and progressive brain dysfunction.
- g. S-transferase a class of enzymes that catalyze the reaction of g. with an acceptor molecule ( E.G., an arene oxide) to form an S-substituted g.; a key step in detoxification of many substances; start of the mercapturic acid pathway. SYN: ligandin.

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glu·ta·thi·one .glüt-ə-'thī-.ōn n a peptide C10H17N3O6S that contains one amino acid residue each of glutamic acid, cysteine, and glycine, that occurs widely in plant and animal tissues, and that plays an important role in biological oxidation-reduction processes and as a coenzyme

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a peptide containing the amino acids glutamic acid, cysteine, and glycine. It functions as a coenzyme in several oxidation-reduction reactions. Glutathione serves as an antioxidant: it reacts with potentially harmful oxidizing agents and is itself oxidized (see also selenium). This is important in ensuring the proper functioning of proteins, haemoglobin, membrane lipids, etc. High levels of glutathione in the blood are associated with longevity.

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glu·ta·thi·one (gloo″tə-thiґōn) a tripeptide, γ-glutamyl-cysteinyl-glycine, that is widely distributed in animal and plant tissues; it exists in both the reduced thiol form (GSH) and the oxidized disulfide form (GSSG). It functions in various redox reactions, such as the destruction of peroxides and free radicals, the detoxification of harmful compounds, and activity as a cofactor for enzymes. In erythrocytes, these reactions prevent oxidative damage by reduction of methemoglobin and peroxides. Glutathione is also involved in the formation and maintenance of disulfide bonds in proteins and in transport of amino acids across cell membranes.

Medical dictionary. 2011.

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