This is a working overview of Tietze assay, written for readers who want more than a one-paragraph summary but less than a textbook.
This page was last updated on 2026-08-01 and is reviewed periodically as new material appears.
Glutathione is a small tripeptide composed of glutamate, cysteine, and glycine, with the unusual gamma-glutamyl linkage between glutamate and cysteine. Its cysteine thiol group makes it a major non-enzymatic antioxidant in cells. The reduced form, GSH, predominates in most intracellular compartments, while the oxidized disulfide form, GSSG, is produced when GSH reduces reactive oxygen species. Intracellular concentrations often reach millimolar levels, whereas plasma concentrations are much lower, typically in the low micromolar range. This gradient reflects active synthesis, transport, and consumption rather than passive distribution.
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.
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.
Quality control for glutathione measurements includes calibration with authenticated standards, internal standards where available, blank correction, and spike recovery checks. Because glutathione can form during sample processing or degrade before analysis, pre-analytical handling is a major source of variability. Interlaboratory comparisons often show differences in reported values due to method-specific calibration and detection principles. Interpretive thresholds are context-dependent, and no single reference range applies across all tissues or matrices. Researchers generally report both reduced and oxidized forms, along with the method and sample handling details.
| Property | Value | Notes |
|---|---|---|
| Molecular formula | C10H17N3O6S | Tripeptide of glutamate, cysteine, and glycine. |
| Molar mass | 307.32 g/mol | Calculated from the molecular formula. |
| Appearance | White to off-white powder | Typically crystalline or lyophilized solid. |
| Solubility | Soluble in water; insoluble in ethanol | Aqueous solutions are acidic and prone to oxidation. |
| Typical storage | -20 °C, desiccated, protect from light | Reduce exposure to oxygen and moisture. |
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.
Biosynthesis occurs in two ATP-dependent steps. The enzyme glutamate-cysteine ligase joins glutamate and cysteine, forming gamma-glutamylcysteine; glutathione synthetase then adds glycine to produce the complete tripeptide. Because the peptide bond from glutamate uses the gamma-carboxyl group, glutathione resists digestion by many ordinary peptidases. Tissues vary in synthesis capacity, and the liver generally contains high concentrations relative to many other organs. This uneven distribution contributes to organ-specific differences in redox buffering and affects how experimental results are interpreted across tissue types.
Quantifying glutathione requires distinguishing GSH from GSSG and preventing oxidation during sample preparation. Common approaches include the enzymatic recycling assay, often called the Tietze method, which measures total glutathione after converting GSSG to GSH. HPLC with ultraviolet or fluorescence detection and LC-MS/MS can separate and quantify both forms, sometimes after derivatization of the thiol group. Blood, plasma, and tissue samples differ in matrix and baseline concentrations, so method validation must account for recovery, linearity, and interference. No single assay is universally standard.
Glutathione is most stable as a dry powder stored cool and dry, but its thiol group is readily oxidized in solution. Aqueous preparations at neutral or alkaline pH lose GSH faster because the thiolate form reacts with dissolved oxygen and metal ions. Acidic conditions, chelating agents, and oxygen exclusion can slow oxidation, while repeated freeze-thaw cycles promote degradation. Light exposure and trace metals also contribute to loss. Laboratories typically validate stability for their own matrices because degradation rates depend on pH, temperature, concentration, and container materials.
Through-bond interactions relate to structural connectivity of the atoms and provide information about which ones are directly connected to each other, connected by way of a single other intermediate atom, etc. Through-space interactions relate to actual geometric distances and angles, including effects of dipolar coupling and the nuclear Overhauser effect. Although the fundamental concept of 2D-FT NMR was proposed by Jean Jeener from the Free University of Brussels at an international conference, this idea was largely developed by Richard Ernst, who won the 1991 Nobel prize in Chemistry for his work in FT NMR, including multi-dimensional FT NMR, and especially 2D-FT NMR of small molecules. Multi-dimensional FT NMR experiments were then further developed into powerful methodologies for studying molecules in solution, in particular for the determination of the structure of biopolymers such as proteins or even small nucleic acids. In 2002 Kurt Wüthrich shared the Nobel Prize in Chemistry (with John Bennett Fenn and Koichi Tanaka) for his work with protein FT NMR in solution.
== Author == Lisa Sanders was born on July 24, 1956, in South Carolina. Sanders grew up loving the idea of mystery and became fond of Arthur Conan Doyle's fictional character, detective Sherlock Holmes. Sanders went to the College of William & Mary where she majored in English. After her graduation in 1979, she was hired by ABC News as a journalist. During her 10-year career as a journalist, Sanders won an Emmy award for her reporting of Hurricane Hugo. She was repeatedly drawn to stories that focused around mysteries and medicine. After about 10 years of reporting, Sanders decided to pursue a career within the medical field. She was accepted into the post-baccalaureate pre-medical program at Columbia University. After completing her pre-medical requirements, she was accepted into Yale Medical School. She completed her residency at Yale and became her class’s chief resident. Sanders became an attending internal medicine physician for the Yale-New Haven Hospital. As her new career progressed, she joined Yale’s Department of Internal Medicine while also teaching primary care at the school of medicine. In 2002, a friend of hers working at The New York Times sparked a conversation about what doctors could provide in a literature perspective. After more discussion, Sanders started writing a column for The New York Times called Diagnosis. The column would highlight medical mysteries that she would encounter with her own patients and those of her colleagues. She described the cases as mysteries, revealing the diagnosis in the following week's column.
=== Renewed intensity (24 March – 7 April) === Following the expiration of temporary ceasefire, Pakistani armed forces carried out a drone strike targeting the 209 Al-Fatah Corps in Balkh province during the night of 24 March, according to local Afghan sources. Taliban officials in Balkh confirmed the presence of drones in the province but denied that the base belonging to 209 Al-Fatah Corps had been struck. Taliban claimed that a civilian was killed and three were wounded in Pakistani artillery shelling in Kunar. On 25 March, Faridun Samim, a spokesperson for the Taliban governor in Nuristan said that Pakistani forces were attacking vehicles attempting to enter Kamdesh and Bargi Matal, forcing the closure of roads to both districts while Taliban authorities sought an alternative route. Afghan local sources had earlier reported that daily Pakistani shelling had made access to the areas difficult. According to those sources, around 40 Taliban fighters had been killed in clashes with Pakistani forces, although the figure was not officially confirmed, and Taliban forces had dispatched two battalions to eastern Nuristan to prevent the border districts from being left undefended. Residents said that communication routes in eastern Nuristan, particularly in Kamdesh and Bargi Matal, had been closed for about 20 days due to clashes and Pakistani attacks, causing severe food shortages and seriously affecting daily life.
Sources: en.wikipedia.org
The US proposal included an end to Iran's nuclear program, limits on its missiles, reopening the Strait of Hormuz, restrictions on Iran's support for armed groups, and sanctions relief for Iran. The Iranians rejected the US proposal, with an anonymous official telling Press TV that "Iran will end the war when it decides to do so and when its own conditions are met". The Iranians issued a "5-point counter-proposal", including an end to US-Israeli attacks on Iran and pro-Iranian forces in Lebanon and Iraq, security guarantees to prevent future Israeli and US aggression, war reparations, and international recognition of Iranian sovereignty over the Strait of Hormuz. On 31 March, Pakistan delivered a "5 point initiative" for peace, calling for an immediate end to all hostilities and allowance of humanitarian aid into the region. Trump claimed on 1 April 2026 that Iran had just asked the US for a ceasefire and that the US would consider it once the Strait of Hormuz was "open, free, and clear. Until then, we are blasting Iran into oblivion ... back to the Stone Ages!". Iran's foreign ministry called the claim "false and baseless". The IRGC said the strait "will not be opened to the enemies of this nation through the ridiculous spectacle by the president of the US". On 8 April 2026, the United States and Iran agreed to a two-week ceasefire in the 2026 Iran war, mediated by Pakistan.
Walgreens subsequently announced a suspension of Theranos blood tests from the Newark lab and immediately paused wellness services in Palo Alto. Theranos also agreed to stop tests at the Capital Blue Cross retail store in Enola, Pennsylvania. In the four months that followed, Theranos faced further action from government agencies. CMS regulators announced plans to enact sanctions that included suspending Holmes and Balwani from owning or operating any certified clinical laboratory for two years and that they would revoke the facility's certification as a clinical laboratory. The company came under criminal investigation by federal prosecutors and the SEC for allegedly misleading investors and government officials about its technology. The U.S. House of Representatives Committee on Energy and Commerce requested information on what Theranos was doing to correct its testing inaccuracies and adherence to federal guidelines. In July 2016, Theranos announced that the CMS had revoked its Clinical Laboratory Improvement Amendments (CLIA) certificate and issued sanctions prohibiting its owners and operators from owning or operating a clinical laboratory for two years, suspension of approval to receive Medicare and Medicaid payments, and a civil monetary penalty. The company discontinued testing at its Newark location while attempting to resolve the issues. Theranos announced plans to appeal the decision by regulators to revoke its license to operate a lab in California and other sanctions.
=== Enzyme probes === To investigate enzymatic activity as opposed to total protein, activity-based reagents have been developed to label the enzymatically active form of proteins (see Activity-based proteomics). For example, serine hydrolase- and cysteine protease-inhibitors have been converted to suicide inhibitors. This strategy enhances the ability to selectively analyze low abundance constituents through direct targeting. Enzyme activity can also be monitored through converted substrate. Identification of enzyme substrates is a problem of significant difficulty in proteomics and is vital to the understanding of signal transduction pathways in cells. A method that has been developed uses "analog-sensitive" kinases to label substrates using an unnatural ATP analog, facilitating visualization and identification through a unique handle.
Sources: en.wikipedia.org
Also, the study by Poullain et al., which is often cited to demonstrate the superiority of whey protein hydrolysate by marketers, measured nitrogen balance in rats after three days of starvation, which corresponds to a longer period in humans. The study found that whey protein hydrolysate led to better nitrogen retention and growth than the other proteins studied. However the study's flaw is in the BV method used, as starvation affects how well the body will store incoming protein (as does a very high caloric intake), leading to falsely elevated BV measures. So, the BV of a protein is related to the amount of protein given. BV is measured at levels below the maintenance level. This means that as protein intake goes up, the BV of that protein goes down. For example, milk protein shows a BV near 100 at intakes of 0.2 g/kg. As protein intake increases to roughly maintenance levels, 0.5 g/kg, BV drops to around 70. Pellet et al., concluded that "biological measures of protein quality conducted at suboptimal levels in either experimental animals or human subjects may overestimate protein value at maintenance levels." As a result, while BV may be important for rating proteins where intake is below requirements, it has little bearing on individuals with protein intakes far above requirements.
== Significance and legacy == In many accounts, the uprising marked the beginning of a sharp upswing in political mobilisation in South Africa and thus "profoundly altered power relations and heralded the beginning of the end of the apartheid regime". In particular, the uprising both revived older modes of non-violent protest – strikes, boycotts, and public demonstrations – and also moulded "a more militant political culture". Indeed, it occasioned a "dramatic increase in the scope of political violence in South Africa": according to the Ministry of Law and Order, the average yearly number of fatalities from political violence exceeded 1,850 per annum from 1985 to 1994, over 100 times the rate of fatalities in the prior nine-year period.
mitotic recombination Also somatic crossing over. The abnormal exchange of genetic material between homologous chromosomes during mitosis (as opposed to meiosis, where it occurs normally). Homologous recombination during mitosis is relatively uncommon; in the laboratory, it can be induced by exposing dividing cells to high-energy electromagnetic radiation such as X rays. As in meiosis, it can separate heterozygous alleles and thereby propagate potentially significant changes in zygosity to daughter cells, though unless it occurs very early in development this often has little or no phenotypic effect, since any phenotypic variance shown by mutant lineages arising in terminally differentiated cells is generally masked or compensated for by neighboring wild-type cells.
Sources: en.wikipedia.org
GSH is the reduced, thiol-containing form of glutathione, while GSSG is the oxidized disulfide dimer formed when two GSH molecules react. Cells maintain a high GSH-to-GSSG ratio under normal conditions. A shift toward GSSG is often interpreted as oxidative stress, though sample handling can affect the measured ratio.
No. It is a tripeptide made from three amino acids: glutamate, cysteine, and glycine. The gamma-glutamyl bond is unusual and distinguishes it from typical peptide linkages.
Most ingested glutathione is broken down in the gastrointestinal tract into its constituent amino acids. Some formulations may protect it from digestion, but intact absorption and delivery to specific tissues remain uncertain. Research continues on precursors and delivery methods.
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.