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Glutathione (GSH, ) is an
antioxidant Antioxidants are compounds that inhibit oxidation, a chemical reaction that can produce free radicals. This can lead to polymerization and other chain reactions. They are frequently added to industrial products, such as fuels and lubrica ...
in plants,
animals Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in ...
,
fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately fr ...
, and some
bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...
and
archaea Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaeba ...
. Glutathione is capable of preventing damage to important cellular components caused by sources such as reactive oxygen species, free radicals,
peroxide In chemistry, peroxides are a group of compounds with the structure , where R = any element. The group in a peroxide is called the peroxide group or peroxo group. The nomenclature is somewhat variable. The most common peroxide is hydrogen p ...
s, lipid peroxides, and
heavy metals upright=1.2, Crystals of osmium, a heavy metal nearly twice as dense as lead">lead.html" ;"title="osmium, a heavy metal nearly twice as dense as lead">osmium, a heavy metal nearly twice as dense as lead Heavy metals are generally defined as ...
. It is a tripeptide with a gamma peptide linkage between the carboxyl group of the
glutamate Glutamic acid (symbol Glu or E; the ionic form is known as glutamate) is an α-amino acid that is used by almost all living beings in the biosynthesis of proteins. It is a non-essential nutrient for humans, meaning that the human body can synt ...
side chain and
cysteine Cysteine (symbol Cys or C; ) is a semiessential proteinogenic amino acid with the formula . The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile. When present as a deprotonated catalytic residue, some ...
. The carboxyl group of the cysteine residue is attached by normal peptide linkage to
glycine Glycine (symbol Gly or G; ) is an amino acid that has a single hydrogen atom as its side chain. It is the simplest stable amino acid ( carbamic acid is unstable), with the chemical formula NH2‐ CH2‐ COOH. Glycine is one of the proteinog ...
.


Biosynthesis and occurrence

Glutathione biosynthesis involves two
adenosine triphosphate Adenosine triphosphate (ATP) is an organic compound that provides energy to drive many processes in living cells, such as muscle contraction, nerve impulse propagation, condensate dissolution, and chemical synthesis. Found in all known forms ...
-dependent steps: *First, γ-glutamylcysteine is synthesized from L-
glutamate Glutamic acid (symbol Glu or E; the ionic form is known as glutamate) is an α-amino acid that is used by almost all living beings in the biosynthesis of proteins. It is a non-essential nutrient for humans, meaning that the human body can synt ...
and
cysteine Cysteine (symbol Cys or C; ) is a semiessential proteinogenic amino acid with the formula . The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile. When present as a deprotonated catalytic residue, some ...
. This conversion requires the enzyme glutamate–cysteine ligase (GCL, glutamate cysteine synthase). This reaction is the rate-limiting step in glutathione synthesis. *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. GCLC
knockout mice A knockout mouse, or knock-out mouse, is a genetically modified mouse (''Mus musculus'') in which researchers have inactivated, or "knocked out", an existing gene by replacing it or disrupting it with an artificial piece of DNA. They are importan ...
die within a month of birth due to the absence of hepatic GSH synthesis. The unusual gamma amide linkage in glutathione protects it from hydrolysis by peptidases.


Occurrence

Glutathione is the most abundant
thiol In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl gro ...
in animal cells, ranging from 0.5 to 10 mmol/L. It is present in the cytosol and the
organelle In cell biology, an organelle is a specialized subunit, usually within a cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as organs are to the body, hence ''organelle,'' th ...
s. Human beings synthesize glutathione, but a few
eukaryote Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacter ...
s do not, including some members of
Fabaceae The Fabaceae or Leguminosae,International Code of Nomenc ...
, ''
Entamoeba ''Entamoeba'' is a genus of Amoebozoa found as internal parasites or commensals of animals. In 1875, Fedor Lösch described the first proven case of amoebic dysentery in St. Petersburg, Russia. He referred to the amoeba he observed microsco ...
'', and ''
Giardia ''Giardia'' ( or ) is a genus of anaerobic flagellated protozoan parasite Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and ...
''. The only known
archaea Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaeba ...
that make glutathione are halobacteria. Some
bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...
, such as "
Cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, bl ...
" and
Pseudomonadota Pseudomonadota (synonym Proteobacteria) is a major phylum of Gram-negative bacteria. The renaming of phyla in 2021 remains controversial among microbiologists, many of whom continue to use the earlier names of long standing in the literature. Th ...
, can biosynthesize glutathione.


Biochemical function

Glutathione exists in reduced (GSH) and oxidized ( GSSG) states. The ratio of reduced glutathione to oxidized glutathione within cells is a measure of cellular oxidative stress where increased GSSG-to-GSH ratio is indicative of greater oxidative stress. In healthy cells and tissue, more than 90% of the total glutathione pool is in the reduced form (GSH), with the remainder in the disulfide form (GSSG). In the reduced state, the thiol group of cysteinyl residue is a source of one reducing equivalent.
Glutathione disulfide Glutathione disulfide (GSSG) is a disulfide derived from two glutathione molecules. In living cells, glutathione disulfide is reduced into two molecules of glutathione with reducing equivalents from the coenzyme NADPH. This reaction is catalyzed ...
(GSSG) is thereby generated. The oxidized state is converted to the reduced state by
NADPH Nicotinamide adenine dinucleotide phosphate, abbreviated NADP or, in older notation, TPN (triphosphopyridine nucleotide), is a cofactor used in anabolic reactions, such as the Calvin cycle and lipid and nucleic acid syntheses, which require NA ...
. This conversion is catalyzed by glutathione reductase: :NADPH + GSSG + H2O → 2 GSH + NADP+ + OH


Roles


Antioxidant

GSH protects cells by neutralising (reducing) reactive oxygen species. This conversion is illustrated by the reduction of peroxides: :2 GSH + R2O2 → GSSG + 2 ROH (R = H, alkyl) and with free radicals: :GSH + R → GSSG + RH


Regulation

Aside from deactivating radicals and reactive oxidants, glutathione participates in thiol protection and redox regulation of cellular thiol proteins under oxidative stress by protein ''S''-glutathionylation, a redox-regulated post-translational thiol modification. The general reaction involves formation of an unsymmetrical disulfide from the protectable protein (RSH) and GSH: :RSH + GSH + → GSSR + H2O Glutathione is also employed for the detoxification of
methylglyoxal Methylglyoxal (MGO) is the organic compound with the formula CH3C(O)CHO. It is a reduced derivative of pyruvic acid. It is a reactive compound that is implicated in the biology of diabetes. Methylglyoxal is produced industrially by degradation ...
and
formaldehyde Formaldehyde ( , ) ( systematic name methanal) is a naturally occurring organic compound with the formula and structure . The pure compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde (refer to section ...
, toxic metabolites produced under oxidative stress. This detoxification reaction is carried out by the
glyoxalase system The glyoxalase system is a set of enzymes that carry out the detoxification of methylglyoxal and the other reactive aldehydes that are produced as a normal part of metabolism. This system has been studied in both bacteria and eukaryotes. This de ...
.
Glyoxalase I The enzyme lactoylglutathione lyase (EC 4.4.1.5, also known as glyoxalase I) catalyzes the isomerization of hemithioacetal adducts, which are formed in a spontaneous reaction between a glutathionyl group and aldehydes such as methylglyoxal. :('' ...
(EC 4.4.1.5) catalyzes the conversion of methylglyoxal and reduced glutathione to ''S''-D-lactoylglutathione. Glyoxalase II (EC 3.1.2.6) catalyzes the hydrolysis of ''S''-D-lactoylglutathione to glutathione and D-lactic acid. It maintains exogenous antioxidants such as vitamins C and E in their reduced (active) states.


Metabolism

Among the many metabolic processes in which it participates, glutathione is required for the biosynthesis of leukotrienes and
prostaglandin The prostaglandins (PG) are a group of physiologically active lipid compounds called eicosanoids having diverse hormone-like effects in animals. Prostaglandins have been found in almost every tissue in humans and other animals. They are deriv ...
s. It plays a role in the storage of cysteine. Glutathione enhances the function of
citrulline The organic compound citrulline is an α-amino acid. Its name is derived from '' citrullus'', the Latin word for watermelon. Although named and described by gastroenterologists since the late 19th century, it was first isolated from watermelon in ...
as part of the
nitric oxide Nitric oxide (nitrogen oxide or nitrogen monoxide) is a colorless gas with the formula . It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes denoted by a dot in its ...
cycle. It is a cofactor and acts on glutathione peroxidase.


Conjugation

Glutathione facilitates metabolism of xenobiotics. Glutathione ''S''-transferase enzymes catalyze its conjugation to lipophilic xenobiotics, facilitating their excretion or further metabolism. The conjugation process is illustrated by the metabolism of ''N''-acetyl-''p''-benzoquinone imine (NAPQI). NAPQI is a reactive
metabolite In biochemistry, a metabolite is an intermediate or end product of metabolism. The term is usually used for small molecules. Metabolites have various functions, including fuel, structure, signaling, stimulatory and inhibitory effects on enzymes, ...
formed by the action of
cytochrome P450 Cytochromes P450 (CYPs) are a superfamily of enzymes containing heme as a cofactor that functions as monooxygenases. In mammals, these proteins oxidize steroids, fatty acids, and xenobiotics, and are important for the clearance of various co ...
on
paracetamol Paracetamol, also known as acetaminophen, is a medication used to treat fever and mild to moderate pain. Common brand names include Tylenol and Panadol. At a standard dose, paracetamol only slightly decreases body temperature; it is inferio ...
(acetaminophen). Glutathione conjugates to NAPQI, and the resulting ensemble is excreted.


Potential neurotransmitters

Glutathione, along with oxidized glutathione (GSSG) and ''S''-nitrosoglutathione (GSNO), bind to the
glutamate Glutamic acid (symbol Glu or E; the ionic form is known as glutamate) is an α-amino acid that is used by almost all living beings in the biosynthesis of proteins. It is a non-essential nutrient for humans, meaning that the human body can synt ...
recognition site of the NMDA and
AMPA receptor The α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (also known as AMPA receptor, AMPAR, or quisqualate receptor) is an ionotropic transmembrane receptor for glutamate ( iGluR) that mediates fast synaptic transmission in the cent ...
s (via their γ-glutamyl moieties). GSH and GSSG may be neuromodulators. At millimolar concentrations, GSH and GSSG may also modulate the redox state of the NMDA receptor complex. Glutathione binds and activates ionotropic receptors, potentially making it a
neurotransmitter A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a synapse. The cell receiving the signal, any main body part or target cell, may be another neuron, but could also be a gland or muscle cell. Neu ...
. GSH activates the purinergic P2X7 receptor from Müller glia, inducing acute
calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar ...
transient signals and GABA release from both
retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which the ...
l neurons and glial cells.


In plants

In plants, glutathione is involved in stress management. It is a component of the glutathione-ascorbate cycle, a system that reduces poisonous
hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3 ...
. It is the precursor of phytochelatins, glutathione
oligomer In chemistry and biochemistry, an oligomer () is a molecule that consists of a few repeating units which could be derived, actually or conceptually, from smaller molecules, monomers.Quote: ''Oligomer molecule: A molecule of intermediate relati ...
s that chelate heavy metals such as
cadmium Cadmium is a chemical element with the Symbol (chemistry), symbol Cd and atomic number 48. This soft, silvery-white metal is chemically similar to the two other stable metals in group 12 element, group 12, zinc and mercury (element), mercury. Li ...
. Glutathione is required for efficient defence against plant pathogens such as ''
Pseudomonas syringae ''Pseudomonas syringae'' is a rod-shaped, Gram-negative bacterium with polar flagella. As a plant pathogen, it can infect a wide range of species, and exists as over 50 different pathovars, all of which are available to researchers from inte ...
'' and '' Phytophthora brassicae''.
Adenylyl-sulfate reductase Adenylyl-sulfate reductase () is an enzyme that catalyzes the chemical reaction of the reduction of adenylyl-sulfate/adenosine-5'-phosphosulfate (APS) to sulfite through the use of an electron donor cofactor. The products of the reaction are AMP ...
, an enzyme of the sulfur assimilation pathway, uses glutathione as an electron donor. Other enzymes using glutathione as a substrate are
glutaredoxin Glutaredoxins (also known as Thioltransferase) are small redox enzymes of approximately one hundred amino-acid residues that use glutathione as a cofactor. In humans this oxidation repair enzyme is also known to participate in many cellular funct ...
s. These small oxidoreductases are involved in flower development,
salicylic acid Salicylic acid is an organic compound with the formula HOC6H4CO2H. A colorless, bitter-tasting solid, it is a precursor to and a metabolite of aspirin (acetylsalicylic acid). It is a plant hormone, and has been listed by the EPA Toxic Substa ...
, and plant defence signalling.


Bioavailability

Systemic availability of orally consumed glutathione is poor because the tripeptide is the substrate of
proteases A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes (increases reaction rate or "speeds up") proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the for ...
(peptidases) of the alimentary canal, and due to the absence of a specific ''carrier'' of glutathione at the level of cell membrane.


Determination of glutathione


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 HCL may refer to: Science and medicine * Hairy cell leukemia, an uncommon and slowly progressing B cell leukemia * Harvard Cyclotron Laboratory, from 1961 to 2002, a proton accelerator used for research and development * Hollow-cathode lamp, a s ...
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 High-performance liquid chromatography (HPLC), formerly referred to as high-pressure liquid chromatography, is a technique in analytical chemistry used to separate, identify, and quantify each component in a mixture. It relies on pumps to p ...
and the fluorescence quantified with a fluorescence detector.


Monochlorobimane

Using monochlorobimane, 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. CMFDA 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 reinterpreted.


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 measurements of glutathione levels in single cells using a confocal microscope, but also be applied in flow cytometry to perform bulk measurements.


RealThiol

The RealThiol (RT) probe is a second-generation reversible reaction-based GSH probe. A few key features of RealThiol: * it has a much faster forward and backward reaction kinetics compared to ThiolQuant Green, which enables real-time monitoring of GSH dynamics in live cells; * only micromolar to sub-micromolar RealThiol is needed for staining in cell-based experiments, which induces minimal perturbation to GSH level in cells; * a high-quantum-yield coumarin fluorophore was implemented so that background noise can be minimized; and * the equilibrium constant of the reaction between RealThiol and GSH has been fine-tuned to respond to physiologically relevant concentration of GSH. RealThiol can be used to perform measurements of glutathione levels in single cells using a high-resolution confocal microscope, as well as be applied in flow cytometry to perform bulk measurements in high throughput manner. An organelle-targeted RT probe has also been developed. A mitochondria-targeted version, MitoRT, was reported and demonstrated in monitoring the dynamic of mitochondrial glutathione both on confocoal microscope and FACS based analysis.


Protein-based glutathione probes

Another approach, which allows measurement of 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). Because of its very low physiological concentration, GSSG is difficult to measure accurately. GSSG concentration ranges from 10 to 50 μM in all solid tissues, and from 2 to 5 μM in blood (13–33 nmol/g Hb). GSH-to-GSSG ratio of whole cell extracts is estimated from 100 to 700. Those ratios represent a mixture from the glutathione pools of different redox states from different subcellular compartments (e.g. more oxidized in the ER, more reduced in the mitochondrial matrix), however. In vivo GSH-to-GSSG ratios can be measured with subcellular accuracy using fluorescent protein-based redox sensors, which have revealed ratios from 50,000 to 500,000 in the cytosol, which implies that GSSG concentration is maintained in the pM range.


Uses


Winemaking

The content of glutathione in
must Must (from the Latin ''vinum mustum'', "young wine") is freshly crushed fruit juice (usually grape juice) that contains the skins, seeds, and stems of the fruit. The solid portion of the must is called pomace and typically makes up 7–23% of th ...
, the first raw form of wine, determines the
browning Browning may refer to: Arts and entertainment * The Browning, an American electronicore band * ''Browning'', a set of variations by the composer William Byrd Places * Browning, Georgia, USA * Browning, Illinois, USA * Browning, Missouri, ...
, or caramelizing effect, during the production of
white wine White wine is a wine that is Fermentation in winemaking, fermented without skin contact. The wine color, colour can be straw-yellow, yellow-green, or yellow-gold. It is produced by the alcoholic fermentation of the non-coloured Juice vesicles, ...
by trapping the caffeoyltartaric acid quinones generated by enzymic oxidation as grape reaction product. Its concentration in wine can be determined by UPLC-MRM mass spectrometry.


See also

*
Reductive stress Reductive stress (RS) is defined as an abnormal accumulation of reducing equivalents despite being in the presence of intact oxidation and reduction systems. A redox reaction involves the transfer of electrons from reducing agents (reductants) to ox ...
*
Glutathione synthetase deficiency Glutathione synthetase deficiency (GSD) is a rare autosomal recessive metabolic disorder that prevents the production of glutathione. Glutathione helps prevent damage to cells by neutralizing harmful molecules generated during energy production. G ...
*
Ophthalmic acid Ophthalmic acid, also known as ophthalmate (chemically L-γ-glutamyl-L-α-aminobutyrylglycine), is a tripeptide analog of glutathione in which the cysteine group is replaced by L-2-aminobutyrate. It was first discovered and isolated from calf le ...
* 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 Glutaredoxins (also known as Thioltransferase) are small redox enzymes of approximately one hundred amino-acid residues that use glutathione as a cofactor. In humans this oxidation repair enzyme is also known to participate in many cellular funct ...
, an antioxidant protein that uses reduced glutathione as a cofactor and is reduced nonenzymatically by it * Bacillithiol * Mycothiol * γ-L-Glutamyl-L-cysteine


References


External links


Glutathione bound to proteins
in the PDB
Benefits & Side Effects

Risk Factors
{{Authority control Thiols Tripeptides Antioxidants Excitatory amino acid receptor ligands Neurotransmitters