freeze-thaw 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 2025-09-05. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
Measuring glutathione in biological samples requires attention to oxidation, because GSH can convert to GSSG after sample collection. Blood and plasma samples are often treated with acid or alkylating agents to preserve the reduced form. Without stabilization, apparent GSH concentrations can fall while GSSG rises. Differences in sample type, handling delay, and deproteinization method can produce results that are not comparable across studies. Reporting preanalytical details is therefore important for interpreting findings.
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.
| 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.
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.
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.
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.
=== Tricyclic antidepressants === TCAs were the first medications that had dual mechanism of action. The mechanism of action of tricyclic secondary amine antidepressants is only partly understood. TCAs have dual inhibition effects on norepinephrine reuptake transporters and serotonin reuptake transporters. Increased norepinephrine and serotonin concentrations are obtained by inhibiting both of these transporter proteins. TCAs have substantially more affinity for norepinephrine reuptake proteins than the SSRIs. This is because of a formation of secondary amine TCA metabolites. In addition, the TCAs interact with adrenergic receptors. This interaction seems to be critical for increased availability of norepinephrine in or near the synaptic clefts. Actions of imipramine-like tricyclic antidepressants have complex, secondary adaptions to their initial and sustained actions as inhibitors of norepinephrine transport and variable blockade of serotonin transport. Norepinephrine interacts with postsynaptic α and β adrenergic receptor subtypes and presynaptic α2 autoreceptors. The α2 receptors include presynaptic autoreceptors which limit the neurophysiological activity of noradrenergic neurons in the central nervous system. Formation of norepinephrine is reduced by autoreceptors through the rate-limiting enzyme tyrosine hydroxylase, an effect mediated by decreased cyclic AMP-mediated phosphorylation-activation of the enzyme. α2 receptors also cause decreased intracellular cyclic AMP expression which results in smooth muscle relaxation or decreased secretion.
However, selegiline can strongly potentiate the reinforcing effects of exogenous β-phenethylamine by inhibiting its MAO-B-mediated metabolism. Misuse of the combination of selegiline and β-phenethylamine has been reported.
=== Discovery and initial characterization === Radioactivity was discovered in 1896 by Henri Becquerel in uranium, and subsequently observed by Marie and Pierre Curie in thorium and in the newly discovered elements polonium and radium. In 1899, Ernest Rutherford separated radioactive emissions into two types: alpha and beta (now beta minus), based on penetration of objects and ability to cause ionization. Alpha rays could be stopped by thin sheets of paper or aluminium, whereas beta rays could penetrate several millimetres of aluminium. In 1900, Paul Villard identified a still more penetrating type of radiation, which Rutherford termed gamma rays. In 1900, Becquerel measured the mass-to-charge ratio (m/e) for beta particles by the method of J.J. Thomson used to study cathode rays and identify the electron. He found that m/e for a beta particle is the same as for Thomson's electron, and therefore suggested that the beta particle is in fact an electron. In 1901, Rutherford and Frederick Soddy showed that alpha and beta radioactivity involves the transmutation of atoms into atoms of other chemical elements. In 1913, after the products of more radioactive decays were known, Soddy and Kazimierz Fajans independently proposed their radioactive displacement law, which states that beta (i.e., β−) emission from one element produces another element one place to the right in the periodic table, while alpha emission produces an element two places to the left.
== Hematopoietic == Acute biphenotypic leukemia Acute eosinophilic leukemia Acute lymphoblastic leukemia Acute myeloid leukemia Acute myeloid dendritic cell leukemia AIDS-related lymphoma Anaplastic large cell lymphoma Angioimmunoblastic T-cell lymphoma B-cell prolymphocytic leukemia Burkitt's lymphoma Chronic lymphocytic leukemia Chronic myelogenous leukemia Cutaneous T-cell lymphoma Diffuse large B-cell lymphoma Follicular lymphoma Hairy cell leukemia Hepatosplenic T-cell lymphoma Hodgkin's lymphoma Intravascular large B-cell lymphoma Large granular lymphocytic leukemia Lymphoplasmacytic lymphoma Lymphomatoid granulomatosis Mantle cell lymphoma Marginal zone B-cell lymphoma Mast cell leukemia Mediastinal large B cell lymphoma Multiple myeloma/plasma cell neoplasm Myelodysplastic syndromes Mucosa-associated lymphoid tissue lymphoma Mycosis fungoides Nodal marginal zone B cell lymphoma Non-Hodgkin lymphoma Precursor B lymphoblastic leukemia Primary central nervous system lymphoma Primary cutaneous follicular lymphoma Primary cutaneous immunocytoma Primary effusion lymphoma Plasmablastic lymphoma Sézary syndrome Splenic marginal zone lymphoma T-cell prolymphocytic leukemia
=== Specific groups === Children and the elderly – The safety and effectiveness of lorazepam are not well determined in children under 18 years of age, but it is used to treat acute seizures. Dose requirements have to be individualized, especially in people who are elderly and debilitated in whom the risk of oversedation is greater. Long-term therapy may lead to cognitive deficits, especially in the elderly, which may only be partially reversible. The elderly metabolize benzodiazepines more slowly than younger people and are more sensitive to the adverse effects of benzodiazepines compared to younger individuals even at similar plasma levels. Additionally, the elderly tend to take more drugs which may interact with or enhance the effects of benzodiazepines. Benzodiazepines, including lorazepam, have been found to increase the risk of falls and fractures in the elderly. As a result, dosage recommendations for the elderly are about half of those used in younger individuals and used for no longer than two weeks. Lorazepam may also be slower to clear in the elderly, leading potentially to accumulation and enhanced effects. Lorazepam, similar to other benzodiazepines and nonbenzodiazepines, causes impairments in body balance and standing steadiness in individuals who wake up at night or the next morning. Falls and hip fractures are frequently reported. The combination with alcohol increases these impairments. Partial, but incomplete, tolerance develops to these impairments.
Sources: en.wikipedia.org
Vitamins occur in a variety of related forms known as vitamers. The vitamers of a given vitamin perform the functions of that vitamin and prevent symptoms of deficiency of that vitamin. Vitamins are those essential organic molecules that are not classified as amino acids or fatty acids. They commonly function as enzymatic cofactors, metabolic regulators or antioxidants. Humans require thirteen vitamins in their diet, most of which are actually groups of related molecules (e.g. vitamin E includes tocopherols and tocotrienols): vitamins A, C, D, E, K, thiamine (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine (B6), biotin (B7), folate (B9), and cobalamin (B12). The requirement for vitamin D is conditional, as people who get sufficient exposure to ultraviolet light, either from the sun or an artificial source, synthesize vitamin D in the skin.
From 1899 to 1901 the six separate self-governing colonies in Australia sent contingents to serve in the war. That much of the population had originated from Britain explains a desire to support it. After the colonies formed the Commonwealth of Australia in 1901, the new Government of Australia sent "Commonwealth" contingents to the war. The Boer War was thus the first war in which the Commonwealth of Australia fought. A few Australians fought on the Boer side. The most famous and colourful character was Colonel Arthur Alfred Lynch, formerly of Ballarat, Victoria, who raised the Second Irish Brigade. The Australian climate and geography were far closer to that of South Africa than most other parts of the empire, so Australians adapted quickly, with troops serving mostly among the army's "mounted rifles". Enlistment in official Australian contingents totalled 16,463. Another five to seven thousand Australians served in "irregular" regiments raised in South Africa. Perhaps 500 Australian irregulars were killed. In total about 20,000 Australians served and about 1,000 were killed. 267 died from disease, 251 were killed in action or from wounds sustained in battle; 43 men were reported missing. When the war began some Australians, like some Britons, opposed it. As the war dragged on some Australians became disenchanted, in part because of the sufferings of Boer civilians reported in the press.
Cultivation of microorganisms does not require fertile soil and therefore does not compete with agriculture. Thanks to the low water requirements, SCP cultivation can even be done in dry climates with infertile soil and may provide a means of fail-safe food supply in arid countries. Photosynthetic microorganisms can reach a higher solar-energy-conversion efficiency than plants, because in photobioreactors supply of water, CO2 and a balanced light distribution can be tightly controlled. Unlike agricultural products which are processed towards a desired quality, it is easier with microorganisms to direct production towards a desired quality. Instead of extracting amino acids from soy beans and throwing away half of the plant body in the process, microorganisms can be genetically modified to overproduce or even secrete a particular amino acid. However, in order to keep a good consumer acceptance, it is usually easier to obtain similar results by screening for microorganisms which already have the desired trait or train them via selective adaptation. Although SCP shows very attractive features as a nutrient for humans, however there are some problems that deter its adoption on global basis:
A glucoside is a glycoside that is chemically derived from glucose. Glucosides are common in plants, but rare in animals. Glucose is produced when a glucoside is hydrolysed by purely chemical means, or decomposed by fermentation or enzymes. The name was originally given to plant products of this nature, in which the other part of the molecule was, in the greater number of cases, an aromatic aldehydic or phenolic compound (exceptions are Jinigrin and Jalapin or Scammonin). It has now been extended to include synthetic ethers, such as those obtained by acting on alcoholic glucose solutions with hydrochloric acid, and also the polysaccharoses, e.g. cane sugar, which appear to be ethers also. Although glucose is the most common sugar present in glucosides, many are known which yield rhamnose or iso-dulcite; these may be termed pentosides. Much attention has been given to the non-sugar parts (aglycone) of the molecules; the constitutions of many have been determined, and the compounds synthesized; and in some cases the preparation of the synthetic glucoside effected. The simplest glucosides are the alkyl ethers which have been obtained by reacting hydrochloric acid on alcoholic glucose solutions. A better method of preparation is to dissolve solid anhydrous glucose in methanol containing hydrochloric acid. A mixture of alpha- and beta-methylglucoside results. The classification of glucosides is a matter of some intricacy.
=== Parts and cleavages === Transcript variant 1 of PIDD1 mRNA in humans, produces a full-length PIDD1 protein consisting of 910 amino acids, with a molecular weight of about 100 kDa. This protein can be broken down into three parts: a 48 kDa N-terminal fragment called PIDD-N, and two C-terminal fragments, PIDD-C (51 kDa) and PIDD-CC (37 kDa). These cleavages occur at positions S446 and S588 through an autoproteolytic process that resembles proteins like inteins or nucleoporin Nup98 undergo self-cleavage. These proteins contain a conserved HSF tripeptide framework that enables a hydrophilic attack of the hydroxyl-group within the serine residue on the preceding peptide bond, converting it into an ester bond that is susceptible to cleavage by an additional nucleophile. The cleavage of full-length PIDD1 (FL-PIDD1) into PIDD-C or PIDD-CC seems to occur constitutively, meaning it happens regularly, which makes FL-PIDD1 levels remain low even when p53 is activated. However, the observation that PIDD-C accumulates before PIDD-CC in response to DNA damage supports the idea that PIDD-C is the primary form generated from FL-PIDD1.
Sources: en.wikipedia.org
== History == The first benchtop detector was introduced in 2014 with detection capabilities between 120 and 240 nm. This portion of the ultraviolet spectrum had historically been restricted to bright source synchrotron facilities due to significant background absorption challenges inherent to working within the wavelength range. Further detector platform development has extended the wavelength detection range out from 120 to 430 nm.
Christianity is an Abrahamic monotheistic religion based on the life and teachings of Jesus of Nazareth. Its adherents, known as Christians, believe that Jesus is the Christ, whose coming as the Messiah was prophesied in the Old Testament, and chronicled in the New Testament. The primary scripture of Christianity is the Bible. It is the world's largest religion with about 2.4 billion followers. Jethro of Midian is considered an ancestor of Druze, who revere him as their spiritual founder and chief prophet. Druzism is a monotheistic and Abrahamic religion based on the teachings of Hamza ibn-'Ali ibn-Ahmad and the sixth Fatimid caliph Al-Hakim bi-Amr Allah, and Greek philosophers such as Plato, Aristotle, Pythagoras, and Zeno of Citium. The Epistles of Wisdom (Rasa'il al-Hikmah; Arabic: رَسَائِل ٱلْحِكْمَة) is the foundational text of the Druze faith. Even though the faith originally developed from Ismaili Islam, the Druze do not identify as Muslims and no longer consider themselves as such. The number of Druze people worldwide is between 800,000 and one million, with the vast majority residing in the Levant. The Druze faith originated in Isma'ilism, further split from it as it developed its own unique doctrines, and finally separated from both Ismāʿīlīsm and Islam altogether; these include the belief that the Imam Al-Ḥākim bi-Amr Allāh was God incarnate. According to various scholars, the Druze faith "diverge substantially from Islam, both Sunni and Shia". Historian David R. W.
=== Women's health === Sexual intercourse between women and circumcised, as compared to uncircumcised, men is associated with a decreased risk of cervical cancer, cervical dysplasia, HSV-2, chlamydia, and syphilis among women. The evidence is less consistent in regard to an association of circumcision with women's risk of HPV and HIV.
== Name == Cold noodles in Chinese cuisine are referred to as liángmiàn (凉面, "chilled noodles"). The term lěngmiàn (冷面, "cold noodles") is mainly associated with Korean-style cold noodles (naengmyeon), which are popular in Northeast China, especially the Yanji-style cold noodles (延吉冷面), a dish of the ethnic Korean communities of the region. Although kǎolěngmiàn contains the word lěngmiàn, the dish is not directly derived from Korean cold noodles. Rather, it developed in Northeast China from starch noodle sheets used in the production of Korean-style cold noodles in the region. As these sheets began to be mass-produced and sold cheaply, street vendors used them to create a grilled snack cooked on charcoal stoves or iron griddles. Vendors commonly market the dish under names such as "Northeast grilled cold noodles" (东北烤冷面), "Heilongjiang grilled cold noodles" (黑龙江烤冷面), and sometimes "Harbin grilled cold noodles" (哈尔滨烤冷面), despite the dish not having originated in Harbin. It is also sometimes marketed as "Korean grilled cold noodles" (朝鲜烤冷面 / 韩国烤冷面) because of its association with Korean-style cold noodles (lěngmiàn) in the name, even though grilled cold noodles themselves did not originate in Korea.
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.