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After the final GSH product is made, it can be used by glutathione peroxidase to neutralize reactive oxygen species (ROS) such as H 2 O 2 or Glutathione S-transferases in the detoxification of xenobiotics. [7] Reaction mechanism for GSH biosynthesis. [14] Glutamate and cysteine side chains are shown in red and green, respectively.
This reaction is the rate-limiting step in glutathione synthesis. [3] Second, glycine is added to the C-terminal of γ-glutamylcysteine. This condensation is catalyzed by glutathione synthetase. While all animal cells are capable of synthesizing glutathione, glutathione synthesis in the liver has been shown to be essential.
Activity of glutathione peroxidase is measured spectrophotometrically using several methods. A direct assay by linking the peroxidase reaction with glutathione reductase with measurement of the conversion of NADPH to NADP is widely used. [11] The other approach is measuring residual GSH in the reaction with Ellman's reagent.
Glutamate–cysteine ligase (GCL) EC 6.3.2.2), previously known as γ-glutamylcysteine synthetase (GCS), is the first enzyme of the cellular glutathione (GSH) biosynthetic pathway that catalyzes the chemical reaction: L-glutamate + L-cysteine + ATP γ-glutamyl cysteine + ADP + P i
Glutathione reductase (GR) also known as glutathione-disulfide reductase (GSR) is an enzyme that in humans is encoded by the GSR gene.Glutathione reductase (EC 1.8.1.7) catalyzes the reduction of glutathione disulfide to the sulfhydryl form glutathione (), which is a critical molecule in resisting oxidative stress and maintaining the reducing environment of the cell.
The detoxification reactions comprise the first four steps of mercapturic acid synthesis, [19] with the conjugation to GSH serving to make the substrates more soluble and allowing them to be removed from the cell by transporters such as multidrug resistance-associated protein 1 . [8]
This reaction is catalyzed by the enzyme glutathione reductase. [2] Antioxidant enzymes, such as glutathione peroxidases and peroxiredoxins, generate glutathione disulfide during the reduction of peroxides such as hydrogen peroxide (H 2 O 2) and organic hydroperoxides (ROOH): [3] 2 GSH + ROOH → GSSG + ROH + H 2 O
The reactive oxygen species then donates one electron to a glutathione molecule, completing the oxidation-reduction reaction and rendering it unable to perform oxidative damage to the cell. [5] After completion of this reaction, glutathione reductase recycles oxidized glutathione back to the reduced form so that it again can be picked up by GSTs.