This is a working overview of oxidation state, written for readers who want more than a one-paragraph summary but less than a textbook.
Reviewed 2025-08-01. Anything still debated is marked as such rather than presented as settled.
Glutathione synthesis proceeds in two ATP-dependent steps catalyzed by glutamate-cysteine ligase and glutathione synthetase. The first step joins glutamate and cysteine to form gamma-glutamylcysteine and is generally rate-limiting. The second step adds glycine to complete the tripeptide. Cysteine availability, feedback inhibition by glutathione, and oxidative conditions influence flux through this pathway. The pathway is conserved across many organisms, and degradation by gamma-glutamyl transpeptidase and related peptidases recycles amino acids for new synthesis.
Within cells, glutathione serves as a cofactor for glutathione peroxidases and glutathione S-transferases. These enzymes reduce hydrogen peroxide and organic peroxides or conjugate electrophilic compounds to the thiol group. The resulting conjugates can be exported and processed through mercapturic acid pathways. Glutathione also contributes to protein thiol homeostasis and to recycling of other antioxidants such as ascorbate. Its precise roles vary by tissue, and many regulatory effects observed in laboratory systems remain difficult to quantify in whole organisms.
Measuring glutathione requires attention to sample preparation because the molecule oxidizes readily. Blood, tissue, and cell samples are often treated with acid to precipitate proteins and stabilize the thiol. Without such steps, GSH can convert to GSSG or form mixed disulfides during storage. Analytical methods include spectrophotometric assays, high-performance liquid chromatography, and mass spectrometry. Each approach has different sensitivity, specificity, and susceptibility to interference from related compounds in complex matrices.
For solid glutathione, storage conditions affect shelf life. The reduced form is typically kept cool, dry, and protected from air and light. Moisture can promote oxidation, while elevated temperatures accelerate degradation. Suppliers often specify storage at or below freezing, sometimes under inert gas. Solutions are less stable than powders and may require preparation shortly before use. Buffers and chelating agents can slow oxidation, but they do not eliminate it. Published stability data vary with matrix, pH, and container.
| Property | Value | Notes |
|---|---|---|
| Common name | Glutathione | Reduced form is abbreviated GSH |
| Chemical class | Tripeptide | Composed of glutamate, cysteine, and glycine |
| Molar mass | 307.32 g/mol | For reduced glutathione |
| CAS Registry Number | 70-18-8 | For reduced L-glutathione |
| Appearance | White crystalline powder | Typical solid reference material |
Glutathione is a tripeptide composed of glutamate, cysteine, and glycine. The peptide bond between glutamate and cysteine uses the gamma-carboxyl group of glutamate rather than the alpha-carboxyl group. This unusual linkage protects the molecule from many common peptidases. The cysteine side chain carries a thiol group that can undergo reversible oxidation. Because of this thiol, glutathione participates in redox reactions and helps maintain the reducing environment inside most cells in living systems.
In cells, glutathione exists mainly in a reduced form called GSH. When two GSH molecules react, they form oxidized glutathione, or GSSG, which contains a disulfide bond. The ratio of GSH to GSSG is often used as an indicator of oxidative stress. Enzymes such as glutathione peroxidase and glutathione reductase help cycle the molecule between these two states. This cycling supports antioxidant defense, detoxification of reactive molecules, and regulation of certain signaling pathways.
Glutathione is present in most tissues, with especially high concentrations in the liver. It also serves as a cofactor for some enzymes and helps transport amino acids across cell membranes. In plants and microorganisms, glutathione contributes to stress responses and metal handling. The molecule is synthesized in two ATP-dependent steps, first producing gamma-glutamylcysteine and then adding glycine. Because cysteine availability often limits synthesis, dietary and metabolic factors can influence glutathione levels. Research continues to examine how these levels relate to health and disease.
Enzymatic recycling assays provide a complementary approach for total glutathione. In these methods, glutathione reductase reduces oxidized glutathione while a thiol-reactive reagent, such as 5,5'-dithiobis(2-nitrobenzoic acid), produces a colored product. The reaction cycles between reduced and oxidized forms, amplifying the signal. Spectrophotometric or fluorometric detection can then estimate concentration. Distinguishing reduced glutathione from glutathione disulfide often requires separate aliquots, masking agents, or chromatographic separation, and the choice affects reported values.
Storage conditions strongly influence glutathione stability. The solid reduced form is commonly kept desiccated at or below minus twenty degrees Celsius, protected from light and moisture. Aqueous solutions are less stable because the thiol group reacts with dissolved oxygen, and oxidation accelerates at neutral or alkaline pH. Acidic solutions and oxygen-free handling can slow degradation, but repeated freeze-thaw cycles should be avoided. Researchers often verify concentration before use, because apparent losses can arise from oxidation or water uptake.
Glutathione functions in redox balance, detoxification, and sulfur amino acid storage. It participates in reactions that help maintain ascorbate and protein thiol status. The molecule serves as a cofactor for several enzymes, including glutathione peroxidases and glutathione S-transferases. These enzymes reduce peroxides and conjugate electrophiles, respectively. Glutathione also contributes to the metabolism of xenobiotics and to the transport of cysteine between tissues. How interorgan transport and tissue-specific regulation shape whole-body pools remains an active area of study.
Glutathione is a tripeptide composed of glutamate, cysteine, and glycine. Its cysteine residue carries a thiol group, which allows the molecule to participate in reduction and oxidation reactions. The compound exists in most living cells, where the reduced form, often abbreviated GSH, is usually more abundant than the oxidized disulfide form, GSSG. Intracellular concentrations are commonly in the millimolar range, while extracellular concentrations are much lower. This uneven distribution supports its role as a major cellular redox buffer.
Cells synthesize glutathione through two ATP-dependent enzymatic steps. The first step combines glutamate and cysteine to form gamma-glutamylcysteine, catalyzed by glutamate-cysteine ligase. The second step adds glycine, producing the complete tripeptide, catalyzed by glutathione synthetase. Glutathione itself can inhibit the first enzyme, providing negative feedback when levels are high. Because cysteine is often limiting, its availability influences how quickly the pathway proceeds. These reactions occur in the cytosol, and the resulting glutathione can be distributed to other compartments.
The nape and the anterior third of the body have irregular pale brown and black cross bars, the black forming rings on the neck. The upper lip is pale brown, with black lines on the sutures between the shields. The lower surface of the head is brownish white. The belly and the ventral surface of the tail are blackish.
== T == T cell – taphonomy – taxis – taxon – taxonomy – telomere – telophase – tertiary structure – testate amoebae – testes – Theodor Bilharz – Theodor Boveri – thermocline – thermoregulation – Thomas Hunt Morgan – Thomas Malthus – thylakoid – Tobacco mosaic virus – tobacco mosaic virus – torpor – Trait (biological) – transcription – transcription factor – transcriptional regulation – transformation – transgressive phenotype – transport vesicle – transposon – Traube cell – trophic level – tropism – tubulin – tumor – turgor – Turner syndrome – twin
=== Heart failure === In heart failure patients, angiotensin receptor blockers such as candesartan and valsartan may be a suitable option for those who do not tolerate angiotensin-converting enzyme inhibitor medicines. Randomised control trials have shown candesartan reduces heart failure hospitalisations and cardiovascular deaths for patients who have heart failure with reduced left ventricular ejection fraction (LVEF ≤ 40%).
Sources: en.wikipedia.org
Within a generation, the Norman elite abandoned Old Norse for the Gallo-Romance language that would evolve into Norman French. They also converted to Christianity, but did so while retaining a distinct warrior ethos. This fusion is evident in the popularity of given names; while Old Norse names like Hrólfr (Rollo) and Ansteinn (Osten) were initially common, they were quickly Latinized or replaced by Christian names, yet the martial spirit remained central to their identity. In many ways they would seem "more French than the French". The descendants of Vikings replaced the Norse religion and Old Norse language with Catholicism (Christianity) and the Langue d'oil of the local people, descending from the Latin of the Romans. The Norman language (Norman French) was forged by the adoption of the indigenous langue d'oïl branch of Romance by a Norse-speaking ruling class, and it developed into the French regional languages that survive today. The new Norman rulers were culturally and ethnically distinct from the old French aristocracy, most of whom traced their lineage to the Franks of the Carolingian dynasty from the days of Charlemagne in the 9th century. By intermarrying with the local aristocracy and adopting the growing feudal doctrines of the rest of France, the Normans would progressively work these principles into a functional hierarchical system in their own duchy, and later export it to Norman dominated England. The Norman population outside the Viking settler elite were overwhelmingly locals of West Francia.
=== Expansion and loss === Typical GSH-Px and superoxide dismutase enzymes requrire trace elements including selenium, vanadium, magnesium, copper, and zinc. These elements tend to be abundant in marine environments but can be lacking in some terrestrial mineral-deficient areas. Organisms have accordingly expanded or reduced their seleno-proteomes (arsenal of selenoproteins) to adapt to the situation. As land plants adapted to the terrestrial environment from about 500 million years ago, they too faced the problem of a lack of these elements. Accordingly, most land plants do not produce selenoproteins. For their anti-oxidation needs, they slowly optimized the production of "new" endogenous antioxidants such as ascorbic acid (Vitamin C), polyphenols (including flavonoids), tocopherols, etc. A few of these appeared more recently, in the last 50–200 million years, in fruits and flowers of angiosperm plants. In fact, the angiosperms (the dominant type of plant today) and most of their antioxidant pigments evolved during the late Jurassic period. The vertebrates of 500 million years ago were marine fishes. They opted to expand their seleno-proteomes, most notably evolving a thyroid gland with high concentration of selenium and iodine and associated systems. A group of them, the tetrapoda, later adapted to life on land but retained many of the ancestral selenoproteins.
These are required for thymidylate and purine production, which are both essential for DNA synthesis and cell division. Pemetrexed is another anti-metabolite that affects purine and pyrimidine production, and therefore also inhibits DNA synthesis. It primarily inhibits the enzyme thymidylate synthase, but also has effects on DHFR, aminoimidazole carboxamide ribonucleotide formyltransferase and glycinamide ribonucleotide formyltransferase. The fluoropyrimidines include fluorouracil and capecitabine. Fluorouracil is a nucleobase analogue that is metabolised in cells to form at least two active products; 5-fluourouridine monophosphate (FUMP) and 5-fluoro-2'-deoxyuridine 5'-phosphate (fdUMP). FUMP becomes incorporated into RNA and fdUMP inhibits the enzyme thymidylate synthase; both of which lead to cell death. Capecitabine is a prodrug of 5-fluorouracil that is broken down in cells to produce the active drug. The deoxynucleoside analogues include cytarabine, gemcitabine, decitabine, azacitidine, fludarabine, nelarabine, cladribine, clofarabine, and pentostatin. The thiopurines include thioguanine and mercaptopurine.
Sources: en.wikipedia.org
Strontium is a divalent silvery metal with a pale yellow tint whose properties are mostly intermediate between and similar to those of its group neighbors calcium and barium. It is softer than calcium and harder than barium. Its melting (777 °C) and boiling (1377 °C) points are lower than those of calcium (842 °C and 1484 °C respectively); barium continues this downward trend in the melting point (727 °C), but not in the boiling point (1900 °C). The density of strontium (2.64 g/cm3) is similarly intermediate between those of calcium (1.54 g/cm3) and barium (3.594 g/cm3). Three allotropes of metallic strontium exist, with transition points at 235 and 540 °C. The standard electrode potential for the Sr(2+)/Sr couple is −2.89 V, approximately midway between those of the Ca(2+)/Ca (−2.84 V) and Ba(2+)/Ba (−2.92 V) couples, and close to those of the neighboring alkali metals. Strontium is intermediate between calcium and barium in its reactivity toward water, with which it reacts on contact to produce strontium hydroxide and hydrogen gas. Strontium metal burns in air to produce both strontium oxide and strontium nitride, but since it does not react with nitrogen below 380 °C, at room temperature it forms only the oxide spontaneously. Besides the simple oxide SrO, the peroxide SrO2 can be made by direct oxidation of strontium metal under a high pressure of oxygen, and there is some evidence for a yellow superoxide Sr(O2)2. Strontium hydroxide, Sr(OH)2, is a strong base, though it is not as strong as the hydroxides of barium or the alkali metals.
== History == Mast cells were first described by Friedrich von Recklinghausen. In 1863 he reported the presence of granulated cells in connective tissues, observed in unstained cells of various species. They were later rediscovered and named in 1878 when Paul Ehrlich described the cells in terms of their unique staining characteristics and large granules. These granules led him to the incorrect belief that they existed to nourish surrounding tissue, so he named them Mastzellen or well-fed cells (from German Mast 'fattening'). In 1937, Holmgren and Wilander found that tissues rich in mast cells also contained large amounts of heparin. In 1952, Riley and West identified mast cells as a storage location for histamine. That mast cells released both heparin and histamine was demonstrated by Rocha e Silva in 1947. As a result of such work MCs became a major focus of allergy research. By 1999, mast cells were considered to be critical sentinel cells in the immune system.
==== Insects ==== In insects, a system involving Malpighian tubules is used to excrete metabolic waste. Metabolic waste diffuses or is actively transported into the tubule, which transports the wastes to the intestines. The metabolic waste is then released from the body along with fecal matter. The excreted material may be called ejecta. In pathology the word ejecta is more commonly used.
Official diplomatic recognition by other countries was key for Rhodesia as it was the only way it could regain the international legitimacy it had lost through UDI. Recognition by the UK itself through a bilateral settlement would be the "first prize", in Smith's words, as it would end sanctions and constitutional ambiguity and make foreign acceptance, at least in the West, far more likely. Considering their country a potentially important player in the Cold War as a "bastion against communism" in southern Africa, the RF posited that some Western countries might recognise UDI even without a prior Anglo-Rhodesian rapprochement. Specifically, it expected diplomatic recognition from South Africa and Portugal, and thought that France might recognise Rhodesia to annoy Britain and create a precedent for an independent Quebec. But although South Africa and Portugal gave economic, military and limited political support to the post-UDI government (as did France and other nations, to a lesser extent), neither they nor any other country ever recognised Rhodesia as a de jure independent state. Rhodesia's unsuccessful attempts to win Western support and recognition included offers to the US government in 1966 and 1967, ignored by Lyndon B. Johnson's administration, to provide Rhodesian troops to fight alongside the Americans and other anti-communist forces in Vietnam.
Sources: en.wikipedia.org
GSH is the reduced thiol form, while GSSG is the disulfide-linked oxidized dimer. The GSH:GSSG ratio is used as a redox indicator, though the ratio can vary with sample handling and cell type.
Glutathione is present in many foods, including meats, poultry, fish, some vegetables, and fruits. Cooking, storage, and digestion affect the amounts available for absorption.
Yes, both enzymatic steps in glutathione synthesis consume ATP. The first step, catalyzed by glutamate-cysteine ligase, is usually rate-limiting.
Common methods include spectrophotometric enzyme cycling assays, HPLC with UV or fluorescence detection, and LC-MS/MS. Detection often requires derivatization because glutathione lacks a strong chromophore. Method choice depends on the sample type and the required sensitivity.