Glutathione (GSH) is a tripeptide. It contains an unusual peptide linkage between the amine group of cysteine and the carboxyl group of the glutamate side chain.
Tissue distribution and concentration
2-5 mM according to the tissue
Cellular GSH homeostasis and GSH-dependent reactions. Intracellular GSH balance is maintained by de novo synthesis, regeneration from GSSG, and extracellular GSH uptake. In transport epithelial cells, such as enterocytes, γ -glutamyl transferase ( γ -GT) and dipeptidase (DP) catalyzed the hydrolysis of extracellular GSH to its constituent amino acids, glutamate, cysteine and glycine. Additionally, intestinal epithelial cells can import intact GSH from the lumen via specifi c plasma membrane transporters. Cytosolic synthesis of GSH takes place in two ATP-dependent reactions catalyzed by glutamate-cysteine ligase (GCL) and glutathione synthase (GS). The intracellular GSH pool, present in millimolar concentrations, is involved in various GSH-dependent reactions. Compartmentation of GSH within the mitochondria, nucleus or endoplasmic reticulum creates distinct and independently regulated subcellular redox pools. As part of the antioxidant defence system, GSH participates in conjugation reactions catalyzed by glutathione-S-transferases (GSTs), in the reduction of hydrogen peroxide (H O ) and lipid hydroperoxides (LOOH) catalyzed by glutathione peroxidases (Gpxs), and the reduction 2 2 of protein-disulfi des (PrSSG) catalyzed by glutaredoxins (Grxs). The reduction of glutathione disulfi de (GSSG) by glutathione reductase (GR) in the GSH redox cycle regenerates GSH. GSSG reduction occurs at the expense of NADPH, produced from the pentose phosphate pathway (PPP) from glucose oxidation.
Glutathione exists in reduced (GSH) and oxidized states. In the reduced state, the thiol group of cysteine is able to donate a reducing equivalent (H++ e-) to other unstable molecules, such as reactive oxygen species. In donating an electron, glutathione itself becomes reactive, but readily reacts with another reactive glutathione to form glutathione disulfide (GSSG).
Such a reaction is possible due to the relatively high concentration of glutathione in cells (up to 5 mM in the liver ).
GSH can be regenerated from GSSG by the enzyme glutathione reductase.
Protein SS groups reduction and Protein/GSH adducts cleavage