Tietze assay comes up often in conversation and rarely with the context attached. Here we lay out the basics in order, then work through the practical considerations.
Last reviewed on 2026-02-16. Where a claim depends on a specific study, the study is described rather than over-claimed.
Storage recommendations for glutathione reagents usually specify a cool, dry, dark environment because the thiol oxidizes in air and light. Solid material is often kept desiccated at low temperature, while solutions are prepared fresh or stored frozen in aliquots. Repeated freeze-thaw cycles can accelerate degradation, and metal ions can catalyze oxidation. Quality control may include purity assays, water content, and identity confirmation. Stability limits are method-specific, so a stated shelf life applies only to defined conditions and packaging.
Laboratory measurement of glutathione requires attention to oxidation before analysis. Blood, tissue, or cell samples can lose reduced glutathione as it converts to GSSG or forms mixed disulfides with proteins. Acid extraction, rapid freezing, and thiol-blocking reagents are common strategies to preserve the original distribution. Reported concentrations therefore depend on collection protocol, extraction method, and the time between sampling and analysis. Comparisons across studies are most reliable when these pre-analytical variables are described.
Common analytical approaches include enzymatic recycling assays, high-performance liquid chromatography, and mass spectrometry. The enzymatic recycling assay uses glutathione reductase and a colorimetric or fluorometric reagent to amplify signal, which gives good sensitivity for total glutathione. Chromatographic methods can separate GSH from GSSG and related thiols, while mass spectrometry offers structural confirmation and multiplexing. Each approach has different requirements for calibration, internal standards, and validation. No single method captures every form of glutathione in every matrix.
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 |
|---|---|---|
| Typical storage temperature | -20 °C or below | For solid reagent and frozen aliquots; protect from moisture and light. |
| Common analytical method | HPLC with UV or fluorescence detection | Separates GSH and GSSG after derivatization or direct detection. |
| Alternative method | LC-MS/MS | Provides high specificity and can quantify multiple thiols. |
| Total glutathione assay | Enzymatic recycling | Uses glutathione reductase and a chromogen or fluorogen. |
| Key stability risk | Oxidation to GSSG | Air, light, and trace metals promote conversion. |
Commercial glutathione is produced by microbial fermentation or chemical synthesis, then purified. Reduced and oxidized grades are offered separately, with purity specifications often exceeding 98 percent. The compound appears in foods such as fresh fruits, vegetables, and meats, although cooking and processing can lower amounts. Oral, topical, and inhaled forms are discussed in research and consumer contexts, but absorption and tissue delivery remain active areas of study. Regulatory status varies by country and intended use.
Glutathione is a small sulfur-containing peptide built from glutamic acid, cysteine, and glycine. Its distinctive feature is a gamma-glutamyl bond between glutamate's side-chain carboxyl group and cysteine's amino group. This linkage resists ordinary peptidases and helps the molecule remain stable inside cells. The reduced thiol form, often abbreviated GSH, is the dominant intracellular species. The oxidized disulfide dimer, GSSG, forms when two reduced molecules link through their cysteine sulfur atoms. The balance between these forms is a common redox indicator.
In living systems, glutathione occurs in millimolar concentrations in many cell types, while extracellular levels are generally much lower. The liver holds a substantial share of the body's total pool, and the molecule participates in reduction, detoxification, and amino acid transport. It also serves as a cofactor for enzymes such as glutathione peroxidase and glutathione S-transferase. Because the cysteine residue supplies a reactive thiol, glutathione can donate electrons and become oxidized. Cells regenerate reduced glutathione through glutathione reductase using NADPH.
Interpreting glutathione measurements requires attention to pre-analytical variables. The GSSG concentration in a sample can rise artificially during storage or processing, making the GSH/GSSG ratio unreliable if not controlled. Reference ranges vary by specimen type, assay, and population, so comparisons across studies are difficult. Plasma glutathione is low and sensitive to hemolysis, while whole blood reflects primarily erythrocyte content. Many studies measure total glutathione rather than the reduced and oxidized forms separately, which limits conclusions about redox status.
Accurate measurement of glutathione begins with careful sample handling. Because GSH oxidizes rapidly to GSSG, samples must be processed quickly or frozen immediately. Acid precipitation with metaphosphoric acid or perchloric acid is common; it lowers pH, precipitates proteins, and helps preserve the reduced form. Chelating agents such as EDTA can limit metal-catalyzed oxidation. For whole blood, hemolysis releases glutathione from erythrocytes, so plasma and serum values differ substantially from whole blood values.
Several analytical methods can quantify glutathione, including high-performance liquid chromatography (HPLC) with UV or fluorescence detection for separating GSH and GSSG. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) offers higher specificity and sensitivity, often detecting nanomolar concentrations. The enzymatic recycling assay, often called the Tietze method, measures total glutathione by coupling reduction of GSSG to a colorimetric or fluorometric readout. Capillary electrophoresis and electrochemical detection are also used in specialized laboratories. Each method has distinct advantages and limitations regarding throughput, cost, and susceptibility to interference.
In December 1975, attempting to circumvent the restrictions of the banning order, the BPC declared Biko their honorary president. After Biko and other BCM leaders were banned, a new leadership arose, led by Muntu Myeza and Sathasivian Cooper, who were considered part of the Durban Moment. Myeza and Cooper organised a BCM demonstration to mark Mozambique's independence from Portuguese colonial rule in 1975. Biko disagreed with this action, correctly predicting that the government would use it to crack down on the BCM. The government arrested around 200 BCM activists, nine of whom were brought before the Supreme Court, accused of subversion by intent. The state claimed that Black Consciousness philosophy was likely to cause "racial confrontation" and therefore threatened public safety. Biko was called as a witness for the defence; he sought to refute the state's accusations by outlining the movement's aims and development. Ultimately, the accused were convicted and imprisoned on Robben Island. In 1973, Biko had enrolled for a law degree by correspondence from the University of South Africa. He passed several exams, but had not completed the degree at his time of death. His performance on the course was poor; he was absent from several exams and failed his Practical Afrikaans module. The state security services repeatedly sought to intimidate him; he received anonymous threatening phone calls, and gun shots were fired at his house. A group of young men calling themselves 'The Cubans' began guarding him from these attacks.
A subunit vaccine is a vaccine that contains purified parts of the pathogen that are antigenic, or necessary to elicit a protective immune response. Subunit vaccine can be made from dissembled viral particles in cell culture or recombinant DNA expression, in which case it is a recombinant subunit vaccine. A "subunit" vaccine doesn't contain the whole pathogen, unlike live attenuated or inactivated vaccine, but contains only the antigenic parts such as proteins, polysaccharides or peptides. Because the vaccine doesn't contain "live" components of the pathogen, there is no risk of introducing the disease, and is safer and more stable than vaccines containing whole pathogens. Other advantages include being well-established technology and being suitable for immunocompromised individuals. Disadvantages include being relatively complex to manufacture compared to some vaccines, possibly requiring adjuvants and booster shots, and requiring time to examine which antigenic combinations may work best. The first recombinant subunit vaccine was produced in the mid-1980s to protect people from Hepatitis B. Other recombinant subunit vaccines licensed include Engerix-B (hepatitis B), Gardasil 9 (Human Papillomavirus), Flublok (influenza), Shingrix (Herpes zoster) and Nuvaxovid (Coronavirus disease 2019). After injection, antigens trigger the production of antigen-specific antibodies, which are responsible for recognising and neutralising foreign substances. Basic components of recombinant subunit vaccines include recombinant subunits, adjuvants and carriers.
Further refinement of the parameters has been achieved through iterative procedures which maximize the agreement between model predictions and a set of experiments, or by leveraging data obtained from all-atom molecular dynamics simulations. Residue-level models of intrinsically disordered proteins have been validated by direct comparison with experimental data, and their predictions have been shown to be accurate across diverse amino acid sequences. Examples of experimental data used to validate the models are radii of gyration of isolated chains and saturation concentrations, which are threshold protein concentrations above which phase separation is observed. Although intrinsically disordered proteins often play important roles in condensate formation, many biomolecular condensates contain multi-domain proteins constituted by folded domains connected by intrinsically disordered regions. Current residue-level models are only applicable to the study of condensates of intrinsically disordered proteins and nucleic acids. Including an accurate description of the folded domains in these models will considerably widen their applicability.
Produced by Patrick Uden, directed by Taghi Amirani, made by Uden Associates 6 August New York! New York!, about sewage; New York makes enough sewage each day to fill the Yankee Stadium ten times, with seven million people; it had 80,000 miles of electric cable; a new sewage tunnel 60 miles long, 800 ft below ground, was being built, to be finished in the next century - the New York City Water Tunnel No. 3 is expected to be finished by 2032 13 August Fatal Attraction, about road transport; Britain subsidised rail £2 per mile, West Germany was £5 per mile; Reinhard Gutter of Cologne; traffic calming hadmainly begun in West Germany, from 1976; John Whitelegg; transport psychologist Carina van Knippenburg of the University of Gronigen; in 1987, the Dutch government introduced rationing of car transport, also trialled in Hong Kong; Ian Catling, and road pricing; Martin Paget in Birmingham; Talib Rothengatter, and the resignation of the Dutch government in April 1989; Philip Goodwin; Martin Mogridge of UCL. Narrated by Simon Ward, produced by Stewart Lansley, directed by Andy Mayer, made by Juniper Productions 20 August The Defender, building a new fighter plane in Canada; Chris Ball, of Bristol Aerospace in Winnipeg, and Bob Diemert are building a fighter plane in Carman, Manitoba; Bob Diemert flew one of his restored Hurricane XII aircraft in the 1969 Battle of Britain; the Commemorative Air Force at Harlingen, Texas; his plane attempts to take off, but it is something akin to a scene from Those Magnificent Men in Their Flying Machines.
°C), which aligns well with modeled results of methane formation temperature and yield. However, some thermogenic methane samples have clumped-isotope temperatures that are unrealistically high. Possible explanations for exceedingly high clumped isotope temperatures include natural gas migration after formation, mixing effect, and kinetic isotope effect of secondary cracking.
Sources: en.wikipedia.org
RFID is often used with track-and-trace solutions, and has a critical role to play in supply chains. RFID is a code-carrying technology, and can be used in place of a barcode to enable non-line of sight-reading. Widespread deployment of RFID has been inhibited by certain limitations of the technology: tag cost, tag readability and privacy issues. The cost of RFID tags currently limits their economic justification for item level tagging or case-level tagging in the produce industry. Reading RFID tags requires specialized equipment limiting their usefulness for consumers today. Product orientation, packing density and materials (in particular water, which is predominant in produce) can have a significant detrimental effect on read reliability of passive tags. Finally, the widespread use of RFID tags on consumer goods is anticipated to be contentious until privacy concerns can be satisfied.
=== 1980s === The compact disk was invented in the 1980s, initially to store and play digital audio recordings but a few years later also as general data storage. Vacuum is used for the metallization of CD surfaces. In 1984, Edwards' Henry Wycliffe invented the Drystar roots/claw dry pump, patented by Edwards. The Drystar was a positive-displacement roots/claw pump that does not require oil for lubrication. The semiconductor industry in particular moved away quickly from oil-sealed pumps in favour of the new dry pumps. In the harsh semiconductor processes, oil-sealed pumps required frequent servicing and oil changes: this new dry pump technology enabled more complex production processes in the semiconductor industry.
The system uses frequency-hopping spread spectrum transmission, in which successive data packets are transmitted in a pseudorandom order on one of 79 1 MHz Bluetooth channels between 2.4 and 2.83 GHz in the ISM band. This allows Bluetooth networks to operate in the presence of noise, other wireless devices and other Bluetooth networks using the same frequencies, since the chance of another device attempting to transmit on the same frequency at the same time as the Bluetooth modem is low. In the case of such a "collision", the Bluetooth modem just retransmits the data packet on another frequency. Packet radio – a long-distance peer-to-peer wireless ad-hoc network in which data packets are exchanged between computer-controlled radio modems (transmitter/receivers) called nodes, which may be separated by miles, and maybe mobile. Each node only communicates with neighboring nodes, so packets of data are passed from node to node until they reach their destination using the X.25 network protocol. Packet radio systems are used to a limited degree by commercial telecommunications companies and by the amateur radio community. Text messaging (texting) – this is a service on cell phones, allowing a user to type a short alphanumeric message and send it to another phone number, and the text is displayed on the recipient's phone screen. It is based on the Short Message Service (SMS) which transmits using spare bandwidth on the control radio channel used by cell phones to handle background functions like dialing and cell handoffs.
regulon A group of non-contiguous genes which are regulated as a unit, generally by virtue of having their expression controlled by the same regulatory element or set of elements, e.g. the same repressor or activator. The term is most commonly used with prokaryotes, where a regulon may consist of genes from multiple operons.
This essay discusses the fairy-story as a literary form. It was initially written as the 1939 Andrew Lang Lecture at the University of St Andrews, Scotland. Tolkien focuses on Andrew Lang's work as a folklorist and collector of fairy tales. He disagreed with Lang's broad inclusion, in his Fairy Book collections, of traveller's tales, beast fables, and other types of stories. Tolkien held a narrower perspective, viewing fairy stories as those that took place in Faerie, an enchanted realm, with or without fairies as characters. He viewed them as the natural development of the interaction of human imagination and human language.
Sources: en.wikipedia.org
Pre-analytical handling, extraction chemistry, and detection method all influence reported glutathione values. Oxidation during sample processing can shift the measured GSH/GSSG ratio. Standardized protocols and reference materials help reduce, but do not eliminate, these differences.
Total glutathione typically refers to the combined amount of reduced glutathione and glutathione disulfide, expressed in glutathione equivalents. Assays that measure total glutathione do not distinguish GSH from GSSG unless a separation step is included. Researchers often pair a total assay with a specific GSSG measurement to estimate the redox ratio.
Glutathione reference standards are generally stored cold, dry, and protected from light. Weighed portions should be prepared promptly and used within validated stability windows. Purity and water content can affect the accuracy of calibration curves.
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.