S-Glutathionylation: From Molecular Mechanisms to Health Outcomes PY2011 IR95 Glutathione as a biological redox buffer

S-Glutathionylation: From Molecular Mechanisms to Health Outcomes PY2011 IR95 Glutathione as a biological redox buffer

資訊來源：

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3110090/

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Glutathione as a biological redox buffer.

重要重點

Glutathione as a biological redox buffer. The ratio of GSH/GSSG reflects the redox capacity of the cell. The ratio is kept in balance through oxidation/reduction reactions involving GSH peroxidase and GSH reductase. Reactive oxygen species-/reactive nitrogen species-induced changes that decrease GSH lead to cell death via apoptosis or necrosis. 

GP, GSH peroxidase; GR, GSH reductase; GSH, reduced glutathione; GSSG, oxidized glutathione.

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重要重點

Intracellular GSH levels are governed by the rate of de novo GSH synthesis and export. GSH cannot freely cross the cell membrane and as such there are GSH transporters in some tissues and enzymes that facilitate catalysis and uptake. In general, GSH must be catabolized via a salvage pathway and the constitutive amino acids brought into the cell for subsequent de novo synthesis. 

重點

To date, only one enzyme is known to facilitate this process. Gamma-glutamyltransferase (GGT) is a cell surface heterodimeric glycoprotein expressed at high levels in kidney tubules, biliary epithelium, and brain capillaries (112). GGT catalyzes the degradation of extracellular GSH, hydrolyzing the γ-glutamyl bond between glutamate and cysteine and releasing the product cysteinyl-glycine (CG) and glutamate. CG is cleaved by the membrane-bound dipeptidase to cysteine and glycine (Fig. 2). The resulting cysteine can be transported into the cell. This salvage supplements the constitutive amino acids required for de novo synthesis, achieved by sequential catalytic steps involving γ-glutamylcysteine synthetase (γ-GCS) and glutathione synthetase. The γ-GCS reaction represents the committed step in the biosynthesis and is subject to feedback inhibition by GSH, but cysteine is rate limiting. Reactions of GSH can be subdivided into those involving the γ-glutamyl and those of the sulfhydryl of cysteine. The amino terminal peptide bond is formed through the γ-carboxyl of the glutamate residue. This bond is resistant to degradation by serum proteolytic enzymes and this allows interorgan transport of GSH.

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