A practical reference on Tietze assay: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
This page was last updated on 2025-07-24 and is reviewed periodically as new material appears.
Common analytical approaches include enzymatic recycling assays, high-performance liquid chromatography, and mass spectrometry. Enzymatic recycling measures total glutathione after converting GSSG back to GSH, while separation methods can quantify GSH and GSSG separately. Derivatization may be used to improve detection or stability during analysis. LC-MS/MS offers high specificity and can distinguish glutathione from related thiols and adducts. Each method has different sensitivity, throughput, and susceptibility to interference, so method selection depends on the study question and sample matrix.
For solid glutathione reagents, storage at low temperature and protection from moisture and light are typical precautions. Aqueous solutions can oxidize over time, and pH affects stability; alkaline conditions generally promote thiol oxidation. Some protocols prepare fresh solutions, while others use antioxidants or chelators to limit metal-catalyzed oxidation. Purity and counterion content can vary among commercial preparations, affecting concentration calculations. Certificates of analysis and validated assays help verify identity and purity.
Quality control for glutathione materials checks identity, assay, purity, water content, and disulfide content. Commercial products vary from research-grade powder to dietary supplements, and labels may not distinguish reduced from oxidized forms. In the United States, oral glutathione is commonly sold as a dietary supplement rather than an approved drug, while injectable forms fall under different rules and may require a prescription. Regulatory status differs by country. Analytical certificates, when available, help verify what a material contains, but independent testing remains important for interpretation.
Laboratory measurement of glutathione typically starts with rapid acid extraction to prevent oxidation and enzymatic degradation. Common methods include enzymatic recycling assays, high-performance liquid chromatography, and liquid chromatography coupled with mass spectrometry. The recycling assay uses glutathione reductase and a thiol-reactive colorimetric or fluorescent reagent, measuring total glutathione after converting disulfide forms. Chromatographic methods can separate reduced and oxidized forms, which helps when the redox ratio is the target. Choice of method affects sensitivity, specificity, and the amount of sample needed.
Samples for glutathione analysis require careful handling because the compound oxidizes readily and can be consumed by enzymes after collection. Blood is often treated with acid or thiol-blocking agents soon after draw, and plasma should be separated quickly from red blood cells. Tissues are usually snap-frozen or extracted immediately. Aqueous solutions of glutathione are less stable than dry powder and degrade faster at neutral or alkaline pH, in light, or with dissolved oxygen. Repeated freeze-thaw cycles also reduce reliability.
| Property | Value | Notes |
|---|---|---|
| Typical analytical method | LC-MS/MS, HPLC, or enzymatic recycling | Choice depends on whether total, reduced, or oxidized glutathione is measured. |
| Sample stabilization | Acidification or thiol alkylation | Helps limit conversion of GSH to GSSG after collection. |
| Solution stability | Limited at room temperature | Oxidation and pH-dependent degradation can occur. |
| Storage of solid | -20 °C, desiccated, protected from light | Common for research reagents; follow supplier instructions. |
| Common interference | Other thiols and metal ions | Can affect separation or enzymatic detection. |
Commercial glutathione is available in research-grade, food-grade, and supplement-grade forms, and purity specifications differ accordingly. Certificates of analysis commonly report identity by nuclear magnetic resonance or mass spectrometry, purity by HPLC, residual solvents, and heavy metals. Reference standards with assigned purity support calibration, while isotopically labeled glutathione can serve as an internal standard for mass spectrometry. For supplements, label claims may not be independently verified, and regulatory oversight varies by country. Verification often involves third-party testing for identity, potency, and contaminants.
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.
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.
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.
==== Asia-Pacific Air Hub ==== UPS's Asia-Pacific Air Hub is located at Singapore Changi Airport. The hub has been expanded by 25% in 2023 to meet the growing e-commerce demand following the pandemic. After the upgrade, it can process 40% more import packages and 45% more export packages, enabling extended pick-up cut-off times for all export services. The hub also features refrigerators and freezers that can maintain temperatures between −20 and 25 °C (−4 and 77 °F) to facilitate the temporary storage of shipments, especially for critical healthcare deliveries such as COVID-19 vaccines. It is part of Changi's cold chain infrastructure, which ensures an unbroken cold chain for pharmaceutical manufacturers.
Many items denoting 'rank and prestige' were deposited in the water surrounding Flag Fen, including swords, spearheads, 'gold earrings, tiny pins and brooches'. Archaeologist Francis Pryor, who discovered the site in 1982, suggests that 'settlers often vied for social status by showing they could afford to discard valuable possessions'. There is also evidence of intentional destruction before placement, e.g. daggers broken in half placed on top of each other. Other finds included small, polished, white stones of a type not known in the area, indicating that they had been intentionally collected and transported to and placed at the site. Other artefacts found were animal bones, including horse mandibles. Horses were very valuable to the prehistoric people, since they provided a means of transport and could supplement or replace man-power. For example, they could be used to carry or pull timbers on sledges over long distances. Significance is also drawn from the discovery of the ritual deposits within thirty metres of the timber post line, and only on its southern boundary. The amount, type, and placement of deposits, which continued for more than 1,200 years, support the theory that 'at least one facet of the site' was a role as a 'religious monument'. On Northey Island many round barrows contemporary with Flag Fen were found. These seemed to be constructed over the dwellings of 'chiefs'. Mike Parker Pearson refers to this as the "Land of the Dead". There is also evidence of farming, including sheep remains, contemporary with the site.
=== Environment === PMOS may also be impacted by epigenetics, which regulates how active genes are. High levels of androgens and AMH during pregnancy and early weight gain can hinder the fetal environment. In studies of PMOS in mice, exposure to AMH or the androgen dihydrotestosterone still has an effect three generations later. If that is so in humans, it implies that PMOS can be inherited via epigenetic changes. Blood in the umbilical cord of babies whose mothers have PMOS shows specific epigenetic changes suggestive of PMOS. There is little evidence on the effect of environmental pollutants on PMOS risk. Hormone disruptors are chemicals that disturb the hormonal system by blocking or mimicking natural hormones. Of these, bisphenol A and phthalates (both used in plastics), and possibly octocrylene exposure may raise the risks of PMOS. Obesity is implicated in PMOS development. As fat tissue can produce androgens, obesity leads to increased androgen levels. It also leads to suppression of the SHBG hormone, increased insulin resistance, and abnormally increased insulin levels. Some of the effects go both ways: PMOS might impact appetite, so that weight gain becomes more likely. Weight loss using diet is equally effective in people with and without PMOS.
Although expression of prolactin receptors have been demonstrated in rat hypothalamus, the same has not been observed in gonadotropin-releasing hormone neurons. Physiologic levels of prolactin in males enhance luteinizing hormone-receptors in Leydig cells, resulting in testosterone secretion, which leads to spermatogenesis. Prolactin also stimulates proliferation of oligodendrocyte precursor cells. These cells differentiate into oligodendrocytes, the cells responsible for the formation of myelin coatings on axons in the central nervous system. Other actions include contributing to pulmonary surfactant synthesis of the fetal lungs at the end of the pregnancy and immune tolerance of the fetus by the maternal organism during pregnancy. Prolactin promotes neurogenesis in maternal and fetal brains. In music psychology, it is conjectured that prolactin may play a role in the pleasurable perception of sad music, as the levels of the hormone increase when a person feels sad, producing a consoling psychological effect.
=== Fold switching === Some proteins have multiple native structures, and change their fold based on some external factors. For example, the KaiB protein switches fold throughout the day, acting as a clock for cyanobacteria. It has been estimated that around 0.5–4% of PDB (Protein Data Bank) proteins switch folds.
Sources: en.wikipedia.org
Shaka was succeeded by Dingane, his half-brother, who conspired with Mhlangana, another half-brother, and Mbopa, an induna, to murder him in 1828. Following this assassination, Dingane murdered Mhlangana, and took over the throne. One of his first royal acts was to execute all of his royal kin. In the years that followed, he also executed many past supporters of Shaka in order to secure his position. One exception to these purges was Mpande, another half-brother, who was considered too weak to be a threat at the time.
Sources: Monocytes; Dendritic cells; Primary T cells; Mast cells; Granulocytes; Macrophages; Adipocytes; Endothelial cells Most complement systems are synthesized by hepatocytes in the liver, however, properdin is synthesized by neutrophils, monocytes, and T cells. Properdin is a positive regulator of the alternative pathway through its mechanism of stabilizing the C3 convertase (C3bBb). Primary T cells, monocytes, macrophages, dendritic cells, granulocytes, and mast cells synthesize mRNA to secrete properdin. Functional properdin is a product of human liver-derived HEP G2 cells. Properdin localized in the granules of neutrophils are released by TNF, TNF/fMLP, PMA, C5a, or IL-8. Additionally, neutrophils promote complement activation upon binding of cytokines, which stabilizes the alternative pathway via release of properdin, increasing defense against microorganisms. Properdin sourced from T cells promote phagocytosis of apoptotic T cells, which is an indication of their function in recognizing and clearing out apoptotic cells. Properdin is also sourced in endothelial cells along with the other complement proteins. Endothelial gene transcripts are induced when shear stress occurs, followed by properdin release into extracellular compartments. Properdin plays an important role in tissue regulation, energy metabolism, and lipid metabolism. An experiment in properdin deficient mice concluded that properdin deficiency results in fat storage and less energy output in comparison to wild-type mice. Properdin regulates fatty acid uptake into adipose tissue.
=== Acetyl-l-carnitine === Acetylcarnitine levels were lower in depressed patients than controls and in rats it causes rapid antidepressant effects through epigenetic mechanisms. A systematic review and meta-analysis of 12 randomized controlled trials found "supplementation significantly decreases depressive symptoms compared with placebo/no intervention, while offering a comparable effect with that of established antidepressant agents with fewer adverse effects."
This low dose of radioiodine is typically tolerated by individuals otherwise allergic to iodine (such as those unable to tolerate contrast mediums containing larger doses of iodine, such as used in CT scan, intravenous pyelogram (IVP), and similar imaging diagnostic procedures). Excess radioiodine that does not get absorbed into the thyroid gland is eliminated by the body in urine. Some people with hyperthyroidism may experience a slight allergic reaction to the diagnostic radioiodine and may be given an antihistamine. The person returns 24 hours later to have the level of radioiodine "uptake" (absorbed by the thyroid gland) measured by a device with a metal bar placed against the neck, which measures the radioactivity emitted from the thyroid. This test takes about 4 minutes while the uptake % (i.e., percentage) is accumulated (calculated) by the machine software. A scan is also performed, wherein images (typically a center, left, and right angle) are taken of the contrasted thyroid gland with a gamma camera; a radiologist will read and prepare a report indicating the uptake % and comments after examining the images. People with hyperthyroidism will typically "take up" higher-than-normal levels of radioiodine. Normal ranges for RAI uptake are from 10 to 30%. In addition to testing the TSH levels, many doctors test for T3, Free T3, T4, and/or Free T4 for more detailed results. Free T4 is unbound to any protein in the blood.
=== Etymology and terminology === The origin of the term dry needling is attributed to Janet G. Travell. In her 1983 book, Myofascial Pain and Dysfunction: Trigger Point Manual, Travell uses the term dry needling to differentiate between two hypodermic needle techniques when performing trigger point therapy. However, Travell did not elaborate on the details of the dry needling techniques: the injection of a local anesthetic and the mechanical use of a hypodermic needle without injecting a solution. The current techniques were based on traditional and Western medical acupuncture.
Sources: en.wikipedia.org
The next incarnation of King Crimson was radically different from the previous configurations. Fripp's four new recruits were free-improvising percussionist Jamie Muir; drummer Bill Bruford, who had left Yes at a critical and commercial peak in their career in favour of the "darker" Crimson; bassist and vocalist John Wetton, who left Family; and violinist, keyboardist and flautist David Cross, whom Fripp had met when he was invited to a rehearsal of Waves, a band Cross was working in. Fripp and Wetton were this incarnation's primary composers, each writing segments independently and fitting together those which they found compatible. With Sinfield gone, the band asked Wetton's friend Richard Palmer-James, formerly of Supertramp, to be their new lyricist. Unlike Sinfield, Palmer-James was not an official member of King Crimson, having no involvement with the band other than writing lyrics, which he would mail to them from his home in Germany. Following a period of rehearsals, King Crimson resumed touring on 13 October 1972 at the Zoom Club in Frankfurt, with the band's penchant for improvisation and Muir's startling stage presence gaining them renewed press attention.
Tea is the most consumed manufactured drink in the world, equalling all others combined, including coffee, soft drinks, and alcohol. Most tea consumed outside East Asia is produced on large plantations in the hilly regions of India and Sri Lanka and is destined to be sold to large businesses. Opposite this large-scale industrial production are many small "gardens," sometimes minuscule plantations, that produce highly sought-after teas prized by gourmets. India is the world's largest tea-drinking nation, although the per capita consumption of tea remains a modest 750 grams (26 oz) per person every year. Turkey, with 2.5 kilograms (5 lb 8 oz) of tea consumed per person per year, is the world's greatest per capita consumer.
=== Top-down methods === Top-down methods adopt some 'force' (e. g. mechanical force, laser) to break bulk materials into nanoparticles. A popular method involves mechanical break apart bulk materials into nanomaterials is 'ball milling'. Besides that, nanoparticles can also be made by laser ablation which apply short pulse lasers (e. g. femtosecond laser) to ablate a target (solid).
embassy vehicles and staff were no longer immune from penalties for traffic violations. American diplomats were asked to show work contracts for all domestic help (cooks, gardeners, drivers and security staff) employed within their households. Indian authorities also conducted an investigation into the American Embassy School. Nancy J. Powell, the U.S. ambassador to India, resigned following the incident, which was widely seen by India "as fallout from the imbroglio." Some commentators suggested that the incident and response could lead to wider damage in U.S.–India relations. Former Finance Minister Yashwant Sinha called for the arrest of same-sex companions of US diplomats, citing the Supreme Court of India's upholding of Section 377 of the Indian Penal Code whereby homosexuality is illegal in India. Former State Department legal advisor John Bellinger questioned whether the decision to arrest and detain Khobragade was "wise policy ... even if technically permissible" under the Vienna Convention on Consular Relations, while Robert D. Blackwill, the former U.S. ambassador to India from 2001 to 2003, said the incident was "stupid." Nevertheless, within a year of the incident, U.S.-India relations were warming again, as U.S. President Obama visited India in January 2015.
Sources: en.wikipedia.org
Preanalytical factors such as sample type, time to processing, and stabilization method can change GSH and GSSG amounts. Analytical method and calibration also contribute to variation. Comparing absolute values across studies requires caution.
These assays typically measure total glutathione after oxidizing or reducing steps convert GSSG to GSH. A colorimetric or fluorometric signal is proportional to the recycling reaction. They generally do not report GSH and GSSG separately unless additional steps are used.
Solutions are often prepared fresh and kept cold, with protection from light and oxygen exposure. Chelating agents may reduce metal-catalyzed oxidation. Storage recommendations vary by buffer, pH, and concentration, so protocol-specific guidance should be followed.
Common approaches include enzymatic recycling assays, HPLC, and LC-MS/MS. Acid extraction and rapid processing limit oxidation before analysis.