If you have been reading about enzymatic recycling assay and want a single page that covers the useful parts, this is it: definitions, context, how it is studied, and the questions that come up repeatedly.
Last reviewed on 2026-04-22. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
Measuring glutathione in biological samples requires attention to oxidation and matrix effects. High-performance liquid chromatography with ultraviolet or fluorescence detection can separate reduced and oxidized forms after derivatization. Liquid chromatography with tandem mass spectrometry offers higher specificity and can quantify glutathione alongside related thiols. Because glutathione can oxidize during sample handling, many protocols use rapid acidification with metaphosphoric acid or sulfosalicylic acid. Internal standards help correct for losses during extraction and analysis.
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.
Glutathione participates in detoxification reactions, amino acid transport, and the maintenance of protein thiols. It serves as a cofactor for several enzymes, including glutathione peroxidases and glutathione S-transferases. In research literature, altered glutathione status appears in studies of aging, infection, metabolic stress, and environmental exposure. Whether low glutathione is a cause, consequence, or marker of such conditions often remains unresolved. Direct measurement in blood or tissue provides a snapshot, but results depend on sample handling, timing, and the method used.
Glutathione is a small tripeptide made of glutamic acid, cysteine, and glycine. Its cysteine thiol group allows reversible oxidation and reduction, making it central to cellular redox chemistry. The reduced form, often abbreviated GSH, predominates inside most cells, while the oxidized disulfide form, GSSG, forms when two GSH molecules react. The ratio of GSH to GSSG is widely used as an indicator of oxidative stress in laboratory research, though it does not by itself diagnose a clinical condition.
| Property | Value | Notes |
|---|---|---|
| Solid storage temperature | -20 °C | Desiccated, protected from light |
| Solution stability | Hours to days at neutral pH | Acidic pH and low oxygen slow oxidation |
| Oxidized form | Glutathione disulfide (GSSG) | Formed by thiol oxidation |
| Typical analytical method | LC-MS/MS or enzymatic recycling | Choice depends on matrix and specificity |
| Thiol pKa | Approximately 9.2 | Influences reactivity at physiological pH |
Quality control for glutathione focuses on identity, purity, and oxidation state. Certificates of analysis may report assay value, water content, and the presence of GSSG or other impurities. Chromatographic purity is often expressed as a percentage of peak area. Reference standards help laboratories compare results across instruments and batches. Because glutathione is a small, polar molecule, separation from cysteine, gamma-glutamylcysteine, and related thiols can be challenging. Verification often combines more than one analytical technique.
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.
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.
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.
Heseltine bought his first Jaguar, second hand and cheap because of the rise in the price of petrol owing to the Suez Crisis, for £1,750 in December 1956, upgrading to newer and more expensive models in future years. New Court Hotel was sold in 1957. At this point Heseltine went into business with another Oxford friend, Clive Labovitch, who brought out Opportunities for Graduates that year. Heseltine arranged for this to be distributed free, expanded from 40 pages to a 169-page hardback book, to final year students at all British universities, paid for by advertising. Heseltine ended his partnership with Josephs and with the aid of a £4,500 investment by Heseltine's mother (following the death of his father in 1957) he and Labovitch were able to buy a group of houses at 29–31 Tregunter Road (south of Earl's Court), adding two more in neighbouring Cathcart Road.
==== Insecticides ==== Scientists are actively seeking methods for controlling the cabbage looper. Known as an evolutionary arms race, scientists are constantly researching ways to control the cabbage looper while the looper evolves resistance to the management methods. Synthetic insecticides are relatively effective; however, many of them are banned for their toxicity. One exception is Ambush. Studies have shown that this pyrethroid insecticide is effective at killing cabbage looper eggs, and its usage is permitted in the US. Other studies have explored the usage of biological insecticides; for example, a polyhedrosis virus was shown to be effective. Unfortunately, managing large quantities of this virus would be difficult, so it is not a feasible option. An effective option is to use synthetic and biological insecticides together; this method seems to both control the population and slow the development of resistance, but it still requires the usage of toxic chemicals. Currently, spraying Bacillus thuringiensis is considered to be the best option, possibly with NPV for an added benefit, but cabbage looper is growing increasingly more resistant to B. thuringiensis. Recent studies, however, have demonstrated that cabbage loopers resistant to B. thuringiensis are twice as susceptible to NPVs, which provides insight into novel biological control methods.
44 (9): 1829. doi:10.1016/0009-2509(89)85125-5. M. König (2008). Herstellung und Charakterisierung nanoporöser Monolithe auf Basis poröser Gläser mit optimierter geometrischer Form zur Anwendung in der Sensortechnik. Diplomarbeit, Halle.
== RNA-DNA world == In 2020, coevolution of a RNA-DNA mixture based on diamidophosphate was proposed. The mixture of RNA-DNA sequences, called chimeras, have weak affinity and form weaker duplex structures. This is advantageous in an abiotic scenario and these chimeras have been shown to replicate RNA and DNA – overcoming the "template-product" inhibition problem, where a pure RNA or pure DNA strand is unable to replicate non-enzymatically because it binds too strongly to its partners. This could lead to an abiotic cross-catalytic amplification of RNA and DNA. A continuous chemical reaction network in water and under high-energy radiation can generate precursors for early RNA. In 2022, evolution experiments of self-replicating RNA showed how RNA may have evolved to diverse complex molecules in RNA world conditions. The RNA evolved to a "replicator network comprising five types of RNAs with diverse interactions" such as cooperation for replication of other members (multiple coexisting host and parasite lineages).
During his 2024 reelection campaign, the Electoral Courts permitted the removal of graffiti that portrayed Melo, partially submerged by flooding. The mural, dubbed Chimelo, was made by the artist Filipe Harp, and was based on an illustration by Bruno Ortiz Monllor. Chimelo was sprayed onto the wall of a cultural center in the Cidade Baixa neighborhood. In a decision rendered on 15 August, Judge Patrícia Hochheim Thomé judged that the panel had been framed as electoral propaganda in the locality or loosely covered by legislation. She ruled that the mural be removed within 24 hours, or be faced with a fine of $5,000 real in case of insubordination, and was rapidly covered up. In September of that year, however, the state Regional Electoral Court (TRE) reauthorized the reproduction of the mural. The art was understood by the Public Electoral Ministry (MPE) was to be interpreted and treated as elaborate art by a citizen who was not running as a candidate. Desembargador Nilton Tavares da Silva agreed with the notion and voted for the mural's authorization. The decision was supported by the court in a unanimous decision.
Sources: en.wikipedia.org
== Hepatic first-pass == After a water-soluble drug is swallowed, it is absorbed by the digestive system and enters the hepatic portal system. It is carried through the portal vein into the liver before it reaches the rest of the body. The liver metabolizes many drugs, sometimes to such an extent that only a small amount of active drug emerges from the liver to the rest of the circulatory system. This first pass through the liver thus may greatly reduce the bioavailability of the drug. An example of a drug where first-pass metabolism is a complication and disadvantage is in the antiviral drug remdesivir. Remdesivir cannot be administered orally because the entire dose would be trapped in the liver with little achieving systemic circulation or reaching target organs and cells (for example, cells infected with SARS-CoV-2). For this reason, remdesivir is administered by IV infusion, bypassing the portal vein. However, significant hepatic extraction still occurs because of second pass metabolism, whereby a fraction of venous blood travels through the hepatic portal vein and hepatocytes.
==== Portugal ==== Cider was once very popular in northern Portugal where its production was larger than wine production until the 11th century, but nowadays, its popularity has decreased and it is mostly consumed in the coasts of Minho, Âncora e Lima, where it is used as a refreshment for thirst. In some festivities, it is still used rather than wine. There is also a traditional production of the drink in Madeira.
Arsenal financed moves for Granit Xhaka and Shkodran Mustafi in mid-2016 for a combined £65 million, rendering the pair one of Arsenal's most expensive ever signings, as Wenger hoped to guide the club to their first league title win in over thirteen years the following season. Although Arsenal began strongly in the league, losing only once until December, back-to-back defeats to Everton and Manchester City resulted in Arsenal losing their stronghold on the league. Wenger also served a four-match touchline ban and had to pay a £25,000 fine after pushing referee Anthony Taylor during a win at home against Burnley. Further defeats to Chelsea and Liverpool all but rendered Arsenal out of the title race, and left qualification to the Champions League threatened by March. On 30 April, Arsenal lost to main rivals Tottenham which had confirmed the latter had finished above them in the Premier League for the first time since the 1994–95 FA Premier League season. The following month also saw them fail to finish in the top four since the 1996–97 FA Premier League season. On 27 May, Wenger became the most successful manager in the history of the FA Cup as Arsenal beat Premier League winners Chelsea 2–1 at Wembley through goals from Alexis Sánchez and Aaron Ramsey. The victory represented a further record for Wenger, as Arsenal too, became the most successful club in the competition's history as they won the competition for the 13th time. Four days following the win, Wenger signed a contract extension until 2019.
==== Withdrawn ==== Amanda Edwards, former at-large Houston city councilor (2016–2020), candidate for U.S. Senate in 2020, candidate for this district in 2024, and runner-up in the 2025–26 special election (remained on ballot)
=== Gastroesophageal junction === The gastroesophageal junction (also known as the esophagogastric junction) is the junction between the esophagus and the stomach, at the lower end of the esophagus. The pink color of the esophageal mucosa contrasts to the deeper red of the gastric mucosa, and the mucosal transition can be seen as an irregular zig-zag line, which is often called the z-line. Histological examination reveals abrupt transition between the stratified squamous epithelium of the esophagus and the simple columnar epithelium of the stomach. Normally, the cardia of the stomach is immediately distal to the z-line and the z-line coincides with the upper limit of the gastric folds of the cardia; however, when the anatomy of the mucosa is distorted in Barrett's esophagus the true gastroesophageal junction can be identified by the upper limit of the gastric folds rather than the mucosal transition. The functional location of the lower oesophageal sphincter is generally situated about 3 cm (1+1⁄4 in) below the z-line.
Sources: en.wikipedia.org
Cardiac markers or cardiac enzymes are proteins that leak out of injured myocardial cells through their damaged cell membranes into the bloodstream. Until the 1980s, the enzymes SGOT and LDH were used to assess cardiac injury. Now, the markers most widely used in detection of MI are MB subtype of the enzyme creatine kinase and cardiac troponins T and I as they are more specific for myocardial injury. The cardiac troponins T and I which are released within 4–6 hours of an attack of MI and remain elevated for up to 2 weeks, have nearly complete tissue specificity and are now the preferred markers for assessing myocardial damage. Heart-type fatty acid binding protein is another marker, used in some home test kits. Elevated troponins in the setting of chest pain may accurately predict a high likelihood of a myocardial infarction in the near future. New markers such as glycogen phosphorylase isoenzyme BB are under investigation. Note that only the cardiac troponins are used clinically for myocardial infarction as creatine kinase adds little value in diagnosing MI while adding to system cost. The diagnosis of myocardial infarction requires two out of three components (history, ECG, and enzymes). When damage to the heart occurs, levels of cardiac markers rise over time, which is why blood tests for them are taken over a 24-hour period.
These were not ready until 1901, the year after the system first opened, and Guimard varied the "Métropolitain" lettering somewhat between stations and twice revised the design, which reached its final form in 1902.
Compounds containing one or more elements which can exist in a variety of charge/oxidation states will have a stoichiometry that depends on which oxidation states are present, to ensure overall neutrality. This can be indicated in the name by specifying either the oxidation state of the elements present, or the charge on the ions. Because of the risk of ambiguity in allocating oxidation states, IUPAC prefers direct indication of the ionic charge numbers. These are written as an arabic integer followed by the sign (... , 2−, 1−, 1+, 2+, ...) in parentheses directly after the name of the cation (without a space separating them). For example, FeSO4 is named iron(2+) sulfate (with the 2+ charge on the Fe2+ ions balancing the 2− charge on the sulfate ion), whereas Fe2(SO4)3 is named iron(3+) sulfate (because the two iron ions in each formula unit each have a charge of 3+, to balance the 2− on each of the three sulfate ions). Stock nomenclature, still in common use, writes the oxidation number in Roman numerals (... , −II, −I, 0, I, II, ...). So the examples given above would be named iron(II) sulfate and iron(III) sulfate respectively. For simple ions the ionic charge and the oxidation number are identical, but for polyatomic ions they often differ. For example, the uranyl(2+) ion, UO2+2, has uranium in an oxidation state of +6, so would be called a dioxouranium(VI) ion in Stock nomenclature.
Glucagon-like peptide-2 (GLP-2) is a 33 amino acid peptide with the sequence HADGSFSDEMNTILDNLAARDFINWLIQTKITD (see Proteinogenic amino acid) in humans. GLP-2 is created by specific post-translational proteolytic cleavage of proglucagon in a process that also liberates the related glucagon-like peptide-1 (GLP-1). GLP-2 is produced by the intestinal endocrine L cell and by various neurons in the central nervous system. Intestinal GLP-2 is co-secreted along with GLP-1 upon nutrient ingestion. When externally administered, GLP-2 produces a number of effects in humans and rodents, including intestinal growth, enhancement of intestinal function, reduction in bone breakdown and neuroprotection. GLP-2 may act in an endocrine fashion to link intestinal growth and metabolism with nutrient intake. GLP-2 and related analogs (such as Teduglutide) may be treatments for short bowel syndrome, Crohn's disease, osteoporosis and as adjuvant therapy during cancer chemotherapy. GLP-2 has an antidepressant effect in a mouse model of depression when delivered via intracerebroventricular injection. However, a GLP-2 derivative (PAS-CPP-GLP-2) was shown to be efficiently delivered to the brain intranasally, with similar efficacy.
Portugal's education system is organised into preschool education; school education, encompassing basic, secondary and higher education; and extracurricular education, which includes continuing education. Optional preschool is provided for all children between three and five years old, after which school attendance is compulsory for 12 years. Basic education lasts nine years and is divided into three cycles, while secondary education is organised into academic and vocational pathways. Higher education is provided by universities and polytechnic institutions in accordance with the Bologna Process, with the University of Lisbon being the country's largest university by enrolment. A general requirement for higher education are the exames finais nacionais do ensino secundário. Most secondary-school students continue their studies at public higher education institutions or the Military Academy, which also awards university degrees. Although other European countries began investing in education in the 19th century, Portugal's long-established national identity, stable borders and homogeneous population contributed to a lack of political commitment to educational development until the First Republic in the early 20th century; many of its reforms were subsequently reversed under the Estado Novo, whose deliberate neglect of education contributed to Portugal recording Europe's highest illiteracy rate in 1964; following democratisation in 1974, education became more widely accessible and underwent modernisation.
Sources: en.wikipedia.org
Chromatographic methods can separate the two forms before detection. Enzymatic assays often measure total glutathione first and then use a separate procedure to estimate the oxidized fraction. The difference between total and oxidized amounts provides an indirect estimate of the reduced form.
Acidification lowers pH and slows thiol oxidation during handling. It also helps precipitate proteins that could interfere with detection. Typical choices include metaphosphoric acid and sulfosalicylic acid.
Dissolved oxygen reacts with the thiol group, forming glutathione disulfide. Neutral and alkaline conditions generally increase the oxidation rate. Light, metal ions, and repeated freezing and thawing can also reduce stability.
GSH is the reduced form of glutathione, with a free thiol group on cysteine. GSSG is the oxidized disulfide form, created when two GSH molecules become linked. The two forms exist together, and their balance is often reported as the GSH/GSSG ratio in laboratory studies.