HPLC 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.
Updated 2026-04-30. Numbers and descriptions here follow the published literature rather than marketing material.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Typical storage temperature | -20 °C or below | Desiccated solid; protect from light |
| Solubility | Soluble in water | Forms acidic solutions |
| Typical analytical method | LC-MS/MS | High specificity for thiols |
| Detection wavelength | 210–220 nm | For HPLC-UV of underivatized glutathione |
| Common synonyms | GSH; reduced glutathione | GSH refers to the reduced form |
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.
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.
Glutathione is a small tripeptide built from glutamate, cysteine, and glycine. The peptide bond between glutamate and cysteine uses the gamma-carboxyl group, a linkage that resists ordinary peptidases. Cells make it in two ATP-dependent steps: gamma-glutamylcysteine synthetase joins glutamate and cysteine, then glutathione synthetase adds glycine. The pathway is feedback-inhibited by glutathione itself, so intracellular levels tend to stay within a narrow range. Because cysteine is often limiting, sulfur amino acid supply influences how much glutathione a cell can produce.
In its reduced form, glutathione carries a sulfhydryl group that can donate electrons. This property lets it act as a major cellular antioxidant and redox buffer. Glutathione peroxidase uses it to reduce hydrogen peroxide and lipid peroxides, while glutathione reductase regenerates the reduced form using NADPH. The ratio of reduced glutathione to glutathione disulfide is widely used as an indicator of oxidative stress, though the ratio changes with compartment, cell type, and sample handling. Oxidized glutathione can also form mixed disulfides with proteins, affecting their activity.
Glutathione supports detoxification by conjugating reactive electrophiles through glutathione S-transferases. The resulting conjugates are processed and exported, often after further metabolism. It also stores cysteine, transports amino acids across membranes through the gamma-glutamyl cycle, and assists in the maturation of iron-sulfur clusters and some prostaglandins. In plants, animals, and many microbes, the molecule appears in similar roles, but concentrations vary enormously between tissues. Liver, kidney, and red blood cells tend to contain high amounts, while blood plasma contains much less.
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.
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.
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.
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.
The NAD-I riboswitch (also called the nadA motif) was identified in species of the bacterial phylum Acidobacteriota, where it typically resides upstream of nadA genes encoding quinolate synthase, an enzyme in the de novo NAD⁺ biosynthesis pathway. Unusually, despite regulating genes relevant to NAD⁺ metabolism, neither binding domain of the NAD⁺-I riboswitch's dual-aptamer architecture has been shown to specifically recognize the nicotinamide portion of the coenzyme; instead, the RNA robustly binds the adenosine 5′-diphosphate (ADP) moiety of NAD⁺.
A throat culture may be done to investigate the cause of a sore throat. Most sore throats are caused by viral infections. However, in some cases the cause of a sore throat may be unclear and a throat culture can be used to determine if the infection is bacterial. Identifying the responsible organism can guide treatment. The person receiving the throat culture is asked to tilt his or her head back and open his or her mouth. The health professional will press the tongue down with a tongue depressor and examine the mouth and throat. A clean swab will be rubbed over the back of the throat, around the tonsils, and over any red areas or sores to collect a sample. The sample may also be collected using a throat washout. For this test, the patient will gargle a small amount of salt water and then spit the fluid into a clean cup. This method gives a larger sample than a throat swab and may make the culture more reliable. A culture for Streptococcus pyogenes can take 18–24 hours when grown at 37 degrees Celsius (body temperature).
== Nitrogen-14 == Nitrogen-14 makes up the clear majority of natural nitrogen, about 99.62%, and is responsible for the Earth's stable atmosphere. Nitrogen-14 is one of the very few stable nuclides with both an odd number of protons and of neutrons (seven each) and is the only one to make up a majority of its element. Unpaired protons or neutrons contribute a half-integer nuclear spin, which in this case is a spin 1/2 orbital, giving the nucleus a total magnetic spin of one (as the spins prefer to align). The original source of nitrogen-14 and nitrogen-15 in the Universe is believed to be stellar nucleosynthesis, where they are produced as part of the CNO cycle. Nitrogen-14 is the source of naturally occurring, radioactive, carbon-14. Some kinds of cosmic radiation cause a nuclear reaction with nitrogen-14 in the upper atmosphere of the Earth, creating carbon-14, which decays back to nitrogen-14 with a half-life of 5700 years.
Sources: en.wikipedia.org
== Manufacturing == Paper-based microfluidic devices can be manufactured based on the dimensions, i.e. 2D and 3D. To fabricate 2D paper-based microfluidics, variations of methods, such as wax printing, inkjet printing, photolithography, flexographic printing, plasma treatment, laser treatment, etching (microfabrication), screen printing, digital light processing (DLP) 3-D printer, and wax screening, have been employed. Further lamination of multiple paper microfluidics creates pseudo-3D microfluidics that could provide an additional dimension of the fluidic network and increase the complexity. Each technique aims to create hydrophobic physical barriers on hydrophilic paper that passively transport aqueous solutions. Biological and chemical reagents must then be deposited selectively along the device by either dipping the substrate into a reagent solution or locally spotting a reagent onto the substrate.
== Career == Beginning in the late 1970s, at Columbia University, Wigler, Richard Axel and Saul Silverstein developed methods for engineering animal cells. These methods are the basis for many discoveries in mammalian genetics, and the means for producing protein therapeutics such as those used to treat heart disease, cancer and strokes. After moving to CSHL, Wigler continued his studies of gene transfer into mammalian cells, exploring the integration of foreign DNA and its stability of expression in host cells, demonstrating the inheritance of DNA methylation patterns, and isolating the first vertebrate genes, and first human oncogenes, using DNA transfer and genetic selection. His laboratory was among the group that first showed the involvement of members of the RAS gene family in human cancer, and that point mutations can activate the oncogenic potential of cellular genes. Wigler's laboratory was the first to demonstrate that some regulatory pathways have been so conserved in evolution that yeast can be used as a host to study the function of mammalian genes and in particular genes involved in signal transduction pathways and cancer. This led to deep insights into RAS function, eventually solving the RAS biochemical pathway in yeast and humans, and demonstrating the multifunctional nature of this important oncogene. From this work in fungi new cellular mechanisms were recognized for "insulating" signal transduction pathways with protein scaffolds that reduce cross-talk and for processing and localization of proteins.
== Treatment == The main focus of treatment for AGAT deficiency is supplementation of creatine, with the goal of replenishing cerebral creatine to normal levels. This is done with oral creatine supplementation. Treatment is most effective if it is started early in life, before symptoms are apparent. Treatment in affected individuals does not reverse intellectual disability or improve cognitive function. For treatment at any age, even if intellectual disability was present, all individuals showed improvement in muscle weakness. In an asymptomatic sibling, who was started on treatment due to the earlier diagnosis of an affected sibling, early intervention with creatine supplementation resulted in improved outcomes when compared to their untreated siblings at the same age. In addition to clinical findings, the effectiveness of treatment can be monitored by following creatine levels in blood and urine as well as the creatine signal by MRS. As creatine is rapidly converted and excreted as creatinine, treatment must be life long to continue to benefit the patient. Treatment during the early years of brain development is most important for preserving brain function.
Elsewhere, armed clashes between Taliban and Pakistan's border guards resumed along the border areas of Khost, Kunar, and Zabul provinces. According to Afghan local sources, clashes in Zabul province caused casualties among Taliban forces and destroyed several border outposts belonging to Taliban forces. In Torkham Border Crossing area, Pakistan officials state that they foiled an infiltration bid and killed an Afghan Taliban commander, identified as Qahraman, along with several of his associates. Pakistan claimed to have killed 67 Talban fighters as they attempted attempted assaults at 16 different locations in northern Balochistan, 27 were killed and several others wounded meanwhile a Frontier Corps soldier was killed and five were injured. 40 more Taliban fighters were killed in an attempted assault in KP. On 4 March, armed clashes between Taliban forces and Pakistani border guards continued in the border areas of Zabul, Kandahar, Khost, and Kunar provinces. An Afghan media outlet quoting local sources in several provinces report that many of the Pakistani strikes in recent days appeared to have targeted Taliban military facilities. They also reported that, over the previous week, the military corps of the Taliban-led Afghan armed forces in Nangarhar province had been struck by the PAF. On the same day, the PAF carried out multiple airstrikes in Kandahar targeting the Taliban-led Afghan armed forces' air brigade, the third battalion of the border police, and the 205 Al-Badr Corps.
Sources: en.wikipedia.org
==== Development of oral antivirals ==== In November 2021, Pfizer launched a new COVID-19 oral antivirus treatment known as Paxlovid. In January 2022, the Pfizer CEO Albert Bourla confirmed that the trial results of a fourth dose were pending until March 2022. He said that the firm was setting up a collaboration to develop an anti-COVID pill treatment along with a French company, Novasep. He also said the COVID vaccine was "safe and efficient" for children. In May 2022, reports emerged of patients experiencing "rebound" symptoms after completing a five-day course of Paxlovid. The FDA responded by announcing they had performed additional analyses of the drug's clinical trial data, and decided against changing its recommendations. U.S. President Joe Biden and Dr. Anthony Fauci were both reported to experience this rebound syndrome in the months that followed, while continuing to recommend the drug for those who may benefit from it.
== Function == Kisspeptin is involved in the regulation of endocrine function and the onset of puberty, with activation of the kisspeptin receptor triggering release of gonadotropin-releasing hormone (GnRH), and release of kisspeptin itself being inhibited by oestradiol but enhanced by GnRH. Reductions in kisspeptin levels with age may conversely be one of the reasons behind age-related declines in levels of other endocrine hormones such as luteinizing hormone.
The president is directly elected by popular vote for a renewable six-year term. Requirements for this position, which were enacted by the PAP government, are extremely stringent, such that only a handful of people qualify for the candidacy. These qualifications include that a candidate needs to be a person at least 45 years of age who is no longer a member of a political party, to either have held public office for at least 3 years in a number of specific public service leadership roles, or to have 3 years experience as chief executive of a fully profitable private sector company with at least S$500 million in shareholders' equity, be a resident in Singapore for at least 10 years, not have a criminal record, and more. Candidates must also "satisfy" the Presidential Elections Committee (PEC) that they are a person of integrity, good character and reputation. From 2017, the Constitution requires that presidential elections be "reserved" for a racial community if no one from that ethnic group has been elected to the presidency in the five most recent terms. Only members of that community may qualify as candidates in a reserved presidential election. In the 2017 presidential election, this combination of stringent requirements and a reserved election that required the candidate to be of the 13% Malay ethnic group led to the PEC approving a single candidate for the presidency; Halimah Yacob, considered part of the Malay community, won in an uncontested election. She also became Singapore's first female president.
Sources: en.wikipedia.org
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.
Blood contains glutathione, but concentrations differ between plasma and red blood cells. Careful separation and rapid processing are needed because ex vivo oxidation and hemolysis can alter results.
An enzymatic recycling assay uses glutathione reductase and a thiol-reactive reagent to generate a signal proportional to total glutathione. It is convenient for many samples but may not distinguish reduced and oxidized forms without additional steps.
Glutathione is a tripeptide made from glutamate, cysteine, and glycine. Its cysteine residue provides a thiol group that is central to its redox activity. The glutamate-cysteine bond forms through the gamma-carboxyl group of glutamate.