Glutathione

Glutathione

Names
IUPAC name (2S)-2-amino-4-{[(1R)-1-[(carboxymethyl)carbamoyl]-2-sulfanylethyl]carbamoyl}butanoic acid
Other names γ-L-Glutamyl-L-cysteinylglycine (2S)-2-Amino-5-[[(2R)-1-(carboxymethylamino)-1-oxo- 3-sulfanylpropan-2-yl]amino]-5-oxopentanoic acid
Identifiers
CAS Number	70-18-8 Y
Abbreviations	GSH
ChEBI	CHEBI:60836 Y
ChEMBL	ChEMBL1543 Y
ChemSpider	111188 Y
DrugBank	DB00143 Y
IUPHAR/BPS	6737
Jmol 3D model	Interactive image
KEGG	C00051 Y
MeSH	Glutathione
PubChem	124886
UNII	GAN16C9B8O Y
InChI InChI=1S/C10H17N3O6S/c11-5(10(18)19)1-2-7(14)13-6(4-20)9(17)12-3-8(15)16/h5-6,20H,1-4,11H2,(H,12,17)(H,13,14)(H,15,16)(H,18,19)/t5-,6-/m0/s1 Y Key: RWSXRVCMGQZWBV-WDSKDSINSA-N Y InChI=1/C10H17N3O6S/c11-5(10(18)19)1-2-7(14)13-6(4-20)9(17)12-3-8(15)16/h5-6,20H,1-4,11H2,(H,12,17)(H,13,14)(H,15,16)(H,18,19)/t5-,6-/m0/s1 Key: RWSXRVCMGQZWBV-WDSKDSINBK
SMILES C(CC(=O)N[C@@H](CS)C(=O)NCC(=O)O)[C@@H](C(=O)O)N
Properties
Chemical formula	C10H17N3O6S
Molar mass	307.32 g·mol−1
Melting point	195 °C (383 °F; 468 K)
Solubility in water	Freely soluble
Solubility in methanol, diethyl ether	Insoluble
Pharmacology
ATC code	V03AB32
Vapor pressure	{{{value}}}
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y verify (what is YN ?)
Infobox references

Glutathione (GSH) is an important antioxidant in plants, animals, fungi, and some bacteria and archaea, preventing damage to important cellular components caused by reactive oxygen species such as free radicals, peroxides, lipid peroxides and heavy metals. It is a tripeptide with a gamma peptide linkage between the carboxyl group of the glutamate side-chain and the amine group of cysteine (which is attached by normal peptide linkage to a glycine).

Thiol groups are reducing agents, existing at a concentration around 5 mM in animal cells. Glutathione reduces disulfide bonds formed within cytoplasmic proteins to cysteines by serving as an electron donor. In the process, glutathione is converted to its oxidized form, glutathione disulfide (GSSG), also called L-(–)-glutathione.

Once oxidized, glutathione can be reduced back by glutathione reductase, using NADPH as an electron donor. The ratio of reduced glutathione to oxidized glutathione within cells is often used as a measure of cellular toxicity.

Biosynthesis

The biosynthesis pathway for glutathione is found in some bacteria, such as cyanobacteria and proteobacteria, but is missing in many other bacteria. Most eukaryotes synthesize glutathione, including humans, but some do not, such as Leguminosae, Entamoeba, and Giardia. The only archaea that make glutathione are halobacteria.

Glutathione is not an essential nutrient for humans, since it can be biosynthesized in the body from the amino acids L-cysteine, L-glutamic acid, and glycine. The sulfhydryl group (SH) of cysteine serves as a proton donor and is responsible for its biological activity. Cysteine is the rate-limiting factor in cellular glutathione biosynthesis, since this amino acid is relatively rare in foods.

Cells make glutathione in two adenosine triphosphate-dependent steps:

• First, gamma-glutamylcysteine is synthesized from L-glutamate and cysteine via the enzyme gamma-glutamylcysteine synthetase (glutamate cysteine ligase, GCL). This reaction is the rate-limiting step in glutathione synthesis.
• Second, glycine is added to the C-terminal of gamma-glutamylcysteine via the enzyme glutathione synthetase.

Animal glutamate cysteine ligase (GCL) is a heterodimeric enzyme composed of a catalytic and a modulatory subunit. The catalytic subunit is necessary and sufficient for all GCL enzymatic activity, whereas the modulatory subunit increases the catalytic efficiency of the enzyme. Mice lacking the catalytic subunit (i.e., lacking all de novo GSH synthesis) die before birth. Mice lacking the modulatory subunit demonstrate no obvious phenotype, but exhibit marked decrease in GSH and increased sensitivity to toxic insults.

While all cells in the human body are capable of synthesizing glutathione, liver glutathione synthesis has been shown to be essential. Mice with genetically induced loss of GCLC (i.e., GSH synthesis) only in the liver die within a month of birth.

The plant glutamate cysteine ligase (GCL) is a redox-sensitive homodimeric enzyme, conserved in the plant kingdom. In an oxidizing environment, intermolecular disulfide bridges are formed and the enzyme switches to the dimeric active state. The midpoint potential of the critical cysteine pair is -318 mV. In addition to the redox-dependent control is the plant GCL enzyme feedback inhibited by GSH. GCL is exclusively located in plastids, and glutathione synthetase is dual-targeted to plastids and cytosol, thus are GSH and gamma-glutamylcysteine exported from the plastids. Both glutathione biosynthesis enzymes are essential in plants; knock-outs of GCL and GS are lethal to embryo and seedling.

Function

Glutathione exists in both reduced (GSH) and oxidized (GSSG) 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 probable 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 (GSR): NADPH reduces FAD present in GSR to produce a transient FADH-anion. This anion then quickly breaks a disulfide bond (Cys58 - Cys63) and leads to Cys63's nucleophilically attacking the nearest sulfide unit in the GSSG molecule (promoted by His467), which creates a mixed disulfide bond (GS-Cys58) and a GS-anion. His467 of GSR then protonates the GS-anion to form the first GSH. Next, Cys63 nucleophilically attacks the sulfide of Cys58, releasing a GS-anion, which, in turn, picks up a solvent proton and is released from the enzyme, thereby creating the second GSH. So, for every GSSG and NADPH, two reduced GSH molecules are gained, which can again act as antioxidants scavenging reactive oxygen species in the cell.

In healthy cells and tissue, more than 90% of the total glutathione pool is in the reduced form (GSH) and less than 10% exists in the disulfide form (GSSG). An increased GSSG-to-GSH ratio is considered indicative of oxidative stress.

Glutathione has multiple functions:

• It is the major endogenous antioxidant produced by the cells, participating directly in the neutralization of free radicals and reactive oxygen compounds, as well as maintaining exogenous antioxidants such as vitamins C and E in their reduced (active) forms.
• Regulation of the nitric oxide cycle is critical for life, but can be problematic if unregulated.
• It is used in metabolic and biochemical reactions such as DNA synthesis and repair, protein synthesis, prostaglandin synthesis, amino acid transport, and enzyme activation. Thus, every system in the body can be affected by the state of the glutathione system, especially the immune system, the nervous system, the gastrointestinal system, and the lungs.
• It has a vital function in iron metabolism. Yeast cells depleted of or containing toxic levels of GSH show an intense iron starvation-like response and impairment of the activity of extramitochondrial ISC enzymes, followed by death.

Function in animals

GSH is known as a substrate in both conjugation reactions and reduction reactions, catalyzed by glutathione S-transferase enzymes in cytosol, microsomes, and mitochondria. However, it is also capable of participating in nonenzymatic conjugation with some chemicals.

In the case of N-acetyl-p-benzoquinone imine (NAPQI), the reactive cytochrome P450-reactive metabolite formed by paracetamol (acetaminophen), which becomes toxic when GSH is depleted by an overdose of acetaminophen, glutathione is an essential antidote to overdose. Glutathione conjugates to NAPQI and helps to detoxify it. In this capacity, it protects cellular protein thiol groups, which would otherwise become covalently modified; when all GSH has been spent, NAPQI begins to react with the cellular proteins, killing the cells in the process. The preferred treatment for an overdose of this painkiller is the administration (usually in atomized form) of N-acetyl-L-cysteine (often as a preparation called Mucomyst), which is processed by cells to L-cysteine and used in the de novo synthesis of GSH.

Glutathione (GSH) participates in leukotriene synthesis and is a cofactor for the enzyme glutathione peroxidase. It is also important as a hydrophilic molecule that is added to lipophilic toxins and waste in the liver during biotransformation before they can become part of the bile. Glutathione is also needed for the detoxification of methylglyoxal, a toxin produced as a byproduct of metabolism.

This detoxification reaction is carried out by the glyoxalase system. Glyoxalase I (EC 4.4.1.5) catalyzes the conversion of methylglyoxal and reduced glutathione to S-D-lactoyl-glutathione. Glyoxalase II (EC 3.1.2.6) catalyzes the hydrolysis of S-D-lactoyl-glutathione to glutathione and D-lactic acid.

Glutathione has recently been used as an inhibitor of melanin in the cosmetics industry. In countries such as Japan and the Philippines, this product is sold as a skin-whitening soap. Glutathione competitively inhibits melanin synthesis in the reaction of tyrosinase and L-DOPA by interrupting L-DOPA's ability to bind to tyrosinase during melanin synthesis. The inhibition of melanin synthesis was reversed by increasing the concentration of L-DOPA, but not by increasing tyrosinase. Although the synthesized melanin was aggregated within one hour, the aggregation was inhibited by the addition of glutathione. These results indicate glutathione inhibits the synthesis and agglutination of melanin by interrupting the function of L-DOPA."

Glutathione, along with oxidized glutathione (GSSG) and S-nitrosoglutathione (GSNO), have been found to bind to the glutamate recognition site of the NMDA and AMPA receptors (via their γ-glutamyl moieties), and may be endogenous neuromodulators. At millimolar concentrations, they may also modulate the redox state of the NMDA receptor complex. In addition, glutathione has been found to bind to and activate ionotropic receptors that are different from any other excitatory amino acid receptor, and which may constitute glutathione receptors, potentially making it a neurotransmitter.

Function in plants

In plants, glutathione is crucial for biotic and abiotic stress management. It is a pivotal component of the glutathione-ascorbate cycle, a system that reduces poisonous hydrogen peroxide. It is the precursor of phytochelatins, glutathione oligomers that chelate heavy metals such as cadmium. Glutathione is required for efficient defence against plant pathogens such as Pseudomonas syringae and Phytophthora brassicae. APS reductase, an enzyme of the sulfur assimilation pathway, uses glutathione as electron donor. Other enzymes using glutathione as substrate are glutaredoxin, these small oxidoreductases are involved in flower development, salicylic acid, and plant defence signalling.

Supplementation

Calcitriol (1,25-dihydroxyvitamin D₃), the active metabolite of vitamin D₃, after being synthesized from calcifediol in the kidney, increases glutathione levels in the brain and appears to be a catalyst for glutathione production. It takes about ten days for the body to process vitamin D₃ into calcitriol.

S-adenosylmethionine (SAMe) has also been shown to increase cellular glutathione content in persons suffering from a disease-related glutathione deficiency.

Low glutathione is commonly observed in wasting and negative nitrogen balance, as seen in cancer, HIV/AIDS, sepsis, trauma, burns, and athletic overtraining.

Methods to determine glutathione

Small molecule based glutathione probes

Ellman's reagent and Monobromobimane

Reduced glutathione may be visualized using Ellman's reagent or bimane derivatives such as monobromobimane. The monobromobimane method is more sensitive. In this procedure, cells are lysed and thiols extracted using a HCl buffer. The thiols are then reduced with dithiothreitol and labelled by monobromobimane. Monobromobimane becomes fluorescent after binding to GSH. The thiols are then separated by HPLC and the fluorescence quantified with a fluorescence detector.

Monochlorobimane

Monochlorobimane can be used to quantify glutathione in vivo. The quantification is done by confocal laser scanning microscopy after application of the dye to living cells. This quantification process relies on measuring the rates of fluorescence changes and is limited to plant cells.

5-Chloromethylfluorescein diacetate (CMFDA)

CMFDA was initially used as a cell tracker. Unfortunately, it has also been mistakenly used as a glutathione probe. Unlike monochlorobimane, whose fluorescence increases upon reacting with glutathione, the fluorescence increase of CMFDA is due to the hydrolysis of the acetate groups inside cells. Although CMFDA may react with glutathione in cells, the fluorescence increase does not reflect the reaction. Therefore, studies using CMFDA as a glutathione probe should be revisited and re-interpreted.

ThiolQuant Green

The major limitation of these bimane based probes and many other reported probes is that these probes are based on irreversible chemical reactions with glutathione, which renders these probes incapable of monitoring the real-time glutathione dynamics. Recently, the first reversible reaction based fluorescent probe-ThiolQuant Green (TQG)-for glutathione was reported. ThiolQuant Green can not only perform high resolution meausrements of glutathione levels in single cells using a confocal microscope, but also be applied in flow cytometry to perform bulk measurements.

Protein based glutathione probes

Another approach, which allows to measure the glutathione redox potential at a high spatial and temporal resolution in living cells is based on redox imaging using the redox-sensitive green fluorescent protein (roGFP) or redox sensitive yellow fluorescent protein (rxYFP) GSSG because its very low physiological concentration is difficult to measure accurately unless the procedure is carefully executed and monitored and the occurrence of interfering compounds is properly addressed. GSSG concentration ranges from 10 to 50 μM in all solid tissues, and from 2 to 5 μM in blood (13–33 nmol per gram Hb). GSH-to-GSSG ratio ranges from 100 to 700.

Uses

Cancer

Once a tumor has been established, elevated levels of glutathione may act to protect cancerous cells by conferring resistance to chemotherapeutic drugs.

Cystic fibrosis

Several studies have been completed on the effectiveness of introducing inhaled glutathione to people with cystic fibrosis with mixed results.

Winemaking

The content of glutathione in "must" determines the browning effect during the production of white wine by trapping the caffeoyltartaric acid quinones generated by enzymic oxidation as grape reaction product. Its concentration in wine can be determined by mass spectrometry.

Cosmetics

Glutathione is a tripeptide molecule found in mammalian bodies. It is an antioxidant that plays an important role in preventing oxidative damage to the skin. In addition to its many recognized biological functions, glutathione has also been associated with skin lightening ability. The role of glutathione as a skin whitening was discovered as a side effect of large doses of glutathione. Glutathione utilizes different mechanisms to exert its action as skin whitening agent at various levels of melanogenesis. It inhibits melanin synthesis by means of stopping L-DOPA’s ability to interact with tyrosinase in the process of melanin production. Research result from a study shows that glutathione inhibits the actual production as well as agglutination of melanin by interrupting the function of L-DOPA. Another study found that glutathione inhibits melanin formation by direct inactivation of the enzyme tyrosinase by binding and chelating copper within the enzyme’s active site. Glutathione’s antioxidant property allows it to inhibit melanin synthesis by quenching of free radicals and peroxides that contribute to tyrosinase activation and melanin formation. Its antioxidant property also protects the skin from UV radiation and other environmental as well as internal stressors that generate free radicals that cause skin damage and hyperpigmentation. In most mammals, melanin formation consists of eumelanin (brown-black pigment) and pheomelanin ( yellow-red pigment) as either mixtures or co-polymers. Increase in glutathione level may induce the pigment cell to produce pheomelanin instead of eumelanin pigments. A research by Te-Sheng Chang found lowest levels of reduced glutathione to be associated with eumelanin type pigmentation, whereas the highest ones were associated with the pheomelanin. As a result, it is reasonable to assume that depletion of glutathione would result in eumelanin formation. Prota observed that decreased glutathione concentration lead to in the conversation of L-Dopaquinone to Dopachrome increasing the formation of brown-black pigment (eumelanin).

See also

• Glutathione synthetase deficiency
• Ophthalmic acid
• roGFP, a tool to measure the cellular glutathione redox potential
• Glutathione-ascorbate cycle
• Bacterial glutathione transferase
• Thioredoxin, a cysteine-containing small proteins with very similar functions as reducing agents
• Glutaredoxin, an antioxidant protein that uses reduced glutathione as a cofactor and is reduced nonenzymatically by it
• Bacillithiol
• Mycothiol

Related research

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External links

• Glutathione bound to proteins in the PDB