The short version of GSH fits in a sentence. The long version — which is the one that helps — is below.
This page was last updated on 2025-08-02 and is reviewed periodically as new material appears.
Glutathione is a tripeptide composed of glutamate, cysteine, and glycine. It contains an unusual gamma-glutamyl bond between glutamate and cysteine, which resists cleavage by many peptidases. The reduced form, GSH, carries a thiol group on cysteine and is the dominant intracellular form in most cells. Its structure allows it to participate in redox reactions and to serve as a sulfur donor. The oxidized form, GSSG, consists of two GSH molecules joined by a disulfide bond.
In cells, glutathione helps maintain the reducing environment of the cytosol and supports enzymes that counteract reactive oxygen species. It acts as a cofactor for glutathione peroxidases, which reduce hydrogen peroxide and lipid peroxides, and for glutathione S-transferases, which conjugate electrophiles. The ratio of GSH to GSSG is often used as an indicator of oxidative stress, although the ratio can vary by compartment and cell type. Glutathione also stores cysteine, an amino acid that can be limiting for protein synthesis and antioxidant defense.
Synthesis occurs in two ATP-dependent steps. The enzyme glutamate-cysteine ligase joins glutamate and cysteine to form gamma-glutamylcysteine, and glutathione synthetase adds glycine. The first step is rate-limiting and is influenced by cysteine availability and feedback inhibition by GSH. Breakdown involves gamma-glutamyl transferase and subsequent peptidases, which release constituent amino acids for reuse. Because turnover differs among tissues, measurements from blood, plasma, and tissues are not directly interchangeable. Research continues to clarify how compartment-specific pools are regulated in health and disease.
Quantification of glutathione in biological or food samples commonly uses liquid chromatography coupled to ultraviolet, fluorescence, electrochemical, or mass spectrometric detection. Because the thiol group oxidizes readily, samples are often acidified or derivatized immediately after collection to stabilize reduced glutathione. Enzymatic recycling assays and colorimetric kits offer higher throughput but generally lower specificity than chromatographic methods. Mass spectrometry can distinguish glutathione from related thiols and allow simultaneous measurement of oxidized forms. Reported concentrations depend strongly on sample type, extraction procedure, and analytical platform.
Glutathione reference materials are sensitive to oxygen, light, and elevated temperature. Solid material is typically stored desiccated at -20 °C or below, while solutions require tighter control because thiol oxidation proceeds faster in liquid form. Aqueous solutions are often prepared fresh, kept cold, and protected from air; some protocols add acid or chelating agents to slow metal-catalyzed oxidation. Repeated freeze-thaw cycles can accelerate degradation and should be avoided. Stability data vary by matrix, so laboratories usually verify performance with their own storage conditions.
| Property | Value | Notes |
|---|---|---|
| Chemical formula | C10H17N3O6S | For reduced glutathione; the oxidized dimer has two sulfur atoms. |
| Molar mass | 307.32 g/mol | Calculated for the reduced form. |
| Appearance | White to off-white crystalline powder | Typical for solid reagent; solutions are usually colorless. |
| Solubility | Freely soluble in water | Poorly soluble in nonpolar organic solvents. |
| Typical storage | -20 °C, desiccated, protected from light | Limits oxidation, moisture uptake, and degradation. |
Glutathione is a small tripeptide built from glutamate, cysteine, and glycine. The peptide bond between glutamate and cysteine uses the gamma-carboxyl group, a linkage that resists ordinary peptidases. Cells make it in two ATP-dependent steps: gamma-glutamylcysteine synthetase joins glutamate and cysteine, then glutathione synthetase adds glycine. The pathway is feedback-inhibited by glutathione itself, so intracellular levels tend to stay within a narrow range. Because cysteine is often limiting, sulfur amino acid supply influences how much glutathione a cell can produce.
In its reduced form, glutathione carries a sulfhydryl group that can donate electrons. This property lets it act as a major cellular antioxidant and redox buffer. Glutathione peroxidase uses it to reduce hydrogen peroxide and lipid peroxides, while glutathione reductase regenerates the reduced form using NADPH. The ratio of reduced glutathione to glutathione disulfide is widely used as an indicator of oxidative stress, though the ratio changes with compartment, cell type, and sample handling. Oxidized glutathione can also form mixed disulfides with proteins, affecting their activity.
Measuring glutathione requires attention to oxidation during sample handling, because GSH in biological samples can convert to GSSG or form mixed disulfides with proteins after collection. Acidic extraction, rapid cooling, and chelating agents are commonly used to limit such changes. Analytical methods usually distinguish free reduced glutathione, total glutathione, and protein-bound forms. Because these forms have different stability and reactivity, reported values depend heavily on the preparation protocol. No single preparation is universally suitable for every biological matrix or analytical goal.
Several techniques are used for quantification. Enzymatic recycling assays rely on glutathione reductase and a colorimetric or fluorescent readout, offering sensitivity for total glutathione. High-performance liquid chromatography can separate GSH from GSSG and other thiols, often with UV, fluorescence, or electrochemical detection. Mass spectrometry provides structural confirmation and can quantify low-abundance species when paired with separation. Each approach has trade-offs in specificity, throughput, and equipment requirements, so method selection depends on the research question and available instrumentation.
Synthesis occurs in two ATP-dependent steps: glutamate-cysteine ligase joins glutamate and cysteine to form gamma-glutamylcysteine, and glutathione synthetase adds glycine to complete the tripeptide. The pathway is feedback-inhibited by GSH and limited by cysteine availability, so cysteine supply often constrains production. Once formed, GSH participates in redox buffering, xenobiotic conjugation, and protein glutathionylation. Glutathione peroxidase uses GSH to reduce hydrogen peroxide and lipid peroxides, yielding GSSG, while glutathione reductase regenerates GSH using NADPH. Glutathione S-transferases conjugate electrophiles to GSH, supporting detoxification and excretion.
Because GSH is central to redox balance, its status is studied in aging, liver disease, neurodegenerative conditions, and metabolic disorders. Observational studies often report lower GSH or higher GSSG in affected tissues, but such associations do not establish that raising glutathione changes disease outcomes. Oral glutathione is digested into amino acids, and whether intact absorption occurs remains debated; precursors such as N-acetylcysteine and cysteine donors are also investigated. Regulatory agencies generally treat glutathione as a dietary supplement, not an approved drug, and clinical claims require evidence from controlled trials.
==== Other optical imaging ==== For in vivo fluorescence-based optical imaging, dyes that emit near infrared (NIR) wavelengths >700 nm are most effective, such as indocyanine green, but encounter limitations with reduced circulation time and nonspecific interactions with other biological factors that affect the fluorescence. pH-sensitive nanogels with functionalized surface receptors to target cancer cells were loaded with a fluorescent dye that was only released upon endocytosis. These nanogels successfully generated a fluorescent signal from within the cancer cells and many other groups have developed similar technologies.
Playground equipment constructed during the Cold War was intended to foster children's curiosity and excitement about the Space Race. It was installed in both Communist and non-Communist countries throughout the Cold War.
The Straw Hats' Jolly Roger became a symbol of Gen Z protests across the world. The flag was first used in protests in Indonesia in October 2023 in Yogyakarta, during protests against the Gaza war. The flag's usage among protester increased during the August 2025 Indonesian protests, also known as the 17+8 movement, consisting of students protesting against the Indonesian House of Representatives allowance hike, and the rising costs of food and education. The usage of the Straw Hats' Jolly Roger gained attention online and spread around the world. Afterwards, other people began to use this flag as well, including the 2025 Philippine anti-corruption protests and many others. The Straw Hats were inspiring since they are "teenagers who fight against an extremely corrupt ruling class" and consistently do this on behalf of the oppressed and marginalized. One participant in the 2025–2026 Philippine anti-corruption protests said, “I don't want my son to grow up in a country full of corrupt officials. I want him to grow up in a country that is peaceful and promotes equality. These characters did not just entertain me throughout my childhood, they taught me values and morals that somewhat made me who I am today. … these fictional characters taught me something that I did not expect will be a factor on how I perceive society as a whole and on what kind of world I would like my son to grow up in.”
Sources: en.wikipedia.org
SR-17018, also known informally as SR-17 or just SR and as 5,6-dichloro-desmethylchlorphine, is an atypical opioid receptor modulator with unusual actions and effects. It acts as a biased partial agonist of the μ-opioid receptor (MOR), showing strong selectivity for activation of G protein signaling over β-arrestin2 recruitment at this receptor. In addition, the drug appears to also act as a MOR positive allosteric modulator, with this possibly being its primary action. Unlike conventional opioids such as morphine and fentanyl, SR-17018 produces robust analgesic effects in rodents with very little respiratory depression and with much less analgesic tolerance. Moreover, substitution of conventional opioids like morphine with SR-17018 can reverse analgesic tolerance and suppress withdrawal symptoms in rodents. However, conflicting findings exist in terms of analgesic tolerance and respiratory depression. The drug has not been formally studied in humans. SR-17018 was first described in the scientific literature by Laura Bohn and colleagues in 2017. It was encountered online as a novel designer drug by 2023. Subsequently, discussion of SR-17018 on the social media website Reddit dramatically increased in 2024. Although technically a designer opioid, SR-17018 is said to have very different effects from other opioids, for instance producing minimal euphoria. Rather than being used recreationally itself, SR-17018 is typically employed by users to prevent opioid withdrawal symptoms and facilitate opioid discontinuation in the context of opioid dependence.
== Mechanism of action == Topotecan is a semi-synthetic derivative of camptothecin. Camptothecin is a natural product extracted from the bark of the tree Camptotheca acuminata. Topoisomerase-I is a nuclear enzyme that relieves torsional strain in DNA by opening single strand breaks. Once topoisomerase-I creates a single strand break, the DNA can rotate in front of the advancing replication fork. In physiological environments, topotecan is in equilibrium with its inactive carboxylate form. Topotecan's active lactone form intercalates between DNA bases in the topoisomerase-I cleavage complex. The binding of topotecan in the cleavage complex prevents topoisomerase-I from religating the nicked DNA strand after relieving the strain. This intercalation therefore traps the topoisomerase-I in the cleavage complex bound to the DNA. When the replication-fork collides with the trapped topoisomerase-I, DNA damage occurs. The unbroken DNA strand breaks and mammalian cells cannot efficiently repair these double strand breaks. The accumulation of trapped topoisomerase-I complexes is a known response to apoptotic stimuli. This disruption prevents DNA replication and ultimately leads to cell death. This process leads to breaks in the DNA strand resulting in apoptosis. Administration of topotecan down-regulates its target, topoisomerase-I; therefore, it is dosed to maximize efficacy and minimize related toxicity. Topotecan is often given in combination with paclitaxel as first line treatment for extensive-stage small-cell lung cancer.
== Reception and legacy == In August 1961, at the International Congress of Biochemistry in Moscow, Nirenberg presented the poly-U experiments – first to a small group, but then at Francis Crick's urging, again to about a thousand attendees. The work was very enthusiastically received, and Nirenberg became famous overnight. The paper describing the work was published the same month. The experiment ushered in a furious race to fully crack the genetic code. Nirenberg's main competition was the esteemed biochemist Severo Ochoa. Dr. Ochoa and Dr. Arthur Kornberg shared the 1959 Nobel Prize in Physiology or Medicine for their previous "discovery of the mechanisms in the biological synthesis of ribonucleic acid and deoxyribonucleic acid." However, many colleagues at the National Institutes of Health (NIH) supported Nirenberg, aware that it may lead to the first Nobel Prize by an intramural NIH scientist. DeWitt Stetten Jr., the NIH director who first hired Nirenberg, called this period of collaboration "NIH's finest hour." Indeed, "for their interpretation of the genetic code and its function in protein synthesis," Marshall W. Nirenberg, Robert W. Holley, and Har Gobind Khorana were awarded the 1968 Nobel Prize in Physiology or Medicine. Working independently, Dr. Holley (Cornell University) had discovered the exact chemical structure of transfer-RNA, and Dr. Khorana (University of Wisconsin in Madison) had mastered the synthesis of nucleic acids. Dr. Nirenberg showed - excluding nonsense codons - every combination of a triplet (i.e.
Sources: en.wikipedia.org
GSH is the reduced form with a free thiol group, while GSSG is the oxidized disulfide-linked dimer. Most assays distinguish the two because their balance reflects redox conditions. The names are not interchangeable.
It is synthesized in the body from amino acids, so it is not classified as an essential dietary nutrient for most people. Dietary and supplemental forms are studied for their effects on tissue levels and health markers. Evidence varies by population and outcome.
The phrase highlights its high intracellular concentration and its role in several antioxidant and detoxification reactions. It is not the only antioxidant, and the term can oversimplify its functions. Scientific descriptions usually specify the pathway or enzyme involved.
Acidification lowers pH and helps prevent oxidation of the thiol group during extraction and storage. It can also precipitate proteins and stabilize the reduced form before analysis.