The short version of LC-MS fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2026-06-10. Anything still debated is marked as such rather than presented as settled.
Animal work has examined the peptide in models of cardiac injury, skin wounding, and corneal repair, with reported outcomes covering cell migration, inflammatory cell influx, and tissue remodeling. Several of those experiments used the full-length protein or longer fragments instead of the seven-residue sequence, which makes direct comparison between reports difficult. Results are generally described as tissue-dependent, and effect sizes vary considerably across laboratories. Independent replication is uneven, so the overall picture is incomplete rather than settled.
Controlled human trials of the short fragment are scarce. Much of what appears in review articles is extrapolated from animal models or from studies of the parent protein, and literature searches return a larger body of cardiac and ophthalmic work on thymosin beta-4 than on the abbreviated peptide. Regulatory treatment differs by jurisdiction, and in several countries the material is handled as a research chemical rather than an approved therapeutic. Statements about human benefit should be read as provisional.
Biological interest in this peptide centers on its relationship to actin dynamics. Thymosin beta-4 binds monomeric actin through an LKKTET motif, and a short sequence carrying that motif can compete with other actin-binding proteins in cell-free preparations. Investigators propose that such competition shifts the balance between filament assembly and disassembly, which in turn affects how readily a cell extends protrusions and migrates. Most of the supporting observations come from cultured cells and purified protein systems rather than from intact organisms.
No major regulatory agency has approved TB-500 for therapeutic use, and it holds no pharmacopoeial monograph. The name appears on the World Anti-Doping Agency prohibited list within the class covering peptide hormones, growth factors, and related substances. Detection in doping control relies on mass spectrometric methods applied to urine, often after preparation steps that concentrate the analyte. Discussion of TB-500 therefore clusters in biochemistry, sports medicine, and anti-doping literature rather than in registered clinical trials.
TB-500 is a synthetic peptide preparation marketed under a name derived from thymosin beta-4, a 43-residue actin-binding protein first isolated from thymus tissue. The full-length protein has a reported molecular mass near 4963 Da, while material sold as TB-500 is often described as a fragment containing the actin-binding motif LKKTETQ. Because suppliers use the name inconsistently, published sources sometimes refer to the same label as a fragment, a synthetic copy, or a related analog. This naming ambiguity complicates direct comparison of reports across studies.
| Property | Value | Notes |
|---|---|---|
| Common synonyms | Thymosin beta-4 fragment; TB4 fragment | Naming is inconsistent across suppliers and publications |
| Reported sequence | Ac-LKKTETQ | Corresponds to residues 17-23 of the parent protein |
| Frequently cited registry number | 77591-33-4 | Associated with full-length thymosin beta-4 rather than the fragment |
| Common supplied form | Freeze-dried solid | Often presented as an acetate or trifluoroacetate salt |
| Regulatory treatment | Varies by country | Frequently handled as a research chemical; not broadly approved as a therapeutic |
The compound circulates in the literature as a research reagent rather than an approved therapeutic. Regulatory agencies in several countries have not authorized it for medical use, and sporting bodies list related thymosin beta-4 peptides among prohibited substances. Suppliers typically market it with a purity figure and a certificate of analysis, while peer-reviewed clinical reports remain sparse. Discussions therefore often separate laboratory findings from anecdotal reports, and reviewers tend to note the small size and methodological limits of the available studies.
TB-500 refers to a synthetic peptide fragment derived from the actin-binding region of thymosin beta-4, a protein present in most mammalian cells. The full protein contains forty-three amino acids, while the commonly sold fragment is a much shorter acetylated sequence, often cited as LKKTETQ. The fragment retains part of the actin-binding motif but lacks the remainder of the parent protein. Material sold under this name is usually lyophilized powder intended for laboratory research, and it is not a finished pharmaceutical product.
Literature and online discussion often conflate TB-500 with full-length thymosin beta-4, even though the two differ in size and are not interchangeable in analytical terms. The fragment is produced by solid-phase peptide synthesis, and the product is a defined seven-residue chain rather than a biological extract. Because the term is a trade-style label, two vendors may supply materials of the same nominal sequence but different counter-ion content, purity, or water content. Comparisons across studies are therefore difficult unless the exact sequence and purity are reported.
TB-500 is a research peptide whose sequence matches residues 17 to 23 of thymosin beta-4, a 43-residue protein present in most mammalian cells. The chain is seven amino acids long, written as LKKTETQ, and is normally supplied with an acetyl group on the N-terminus. Suppliers list it as a lyophilised powder under the code name TB-500, and the same sequence appears elsewhere in catalogues as the thymosin beta-4 actin-binding fragment. The label is commercial rather than systematic, so no single authority fixes exactly what TB-500 denotes.
Thymosin beta-4 was isolated from calf thymus in the early 1980s and later characterised as an abundant intracellular actin-sequestering protein. Interest in short synthetic fragments grew once the actin-binding motif had been mapped to the middle of the sequence. TB-500 came out of that line of work as a truncated analogue rather than a natural isolate, and it is now sold mainly to laboratories. Published studies on the fragment have been largely in vitro or in animal models, and controlled human trials remain sparse, so claims about effects in people rest on extrapolation.
Identity and purity are checked with chromatographic and mass spectrometric methods. Reverse-phase high-performance liquid chromatography separates the peptide from related impurities, while mass spectrometry confirms the expected molecular mass. A certificate of analysis may report a purity percentage, but the laboratory should still verify the material independently. Common quality concerns include truncated sequences, deamidation, oxidation, and residual solvents from synthesis. Because TB-500 is short, some impurities can differ from the target by only a few mass units.
Reconstitution practices affect downstream measurements. The dry powder is typically dissolved in sterile water or a suitable aqueous buffer, then mixed gently rather than vortexed at high speed. Visible particles or cloudiness suggest incomplete dissolution or contamination and should be investigated. For long-term storage, aliquots should be labeled with concentration, solvent, and date. Open questions include how different buffers alter peptide conformation and whether specific container materials adsorb the peptide. Those variables can change apparent concentration in assays even when the chemical identity is correct.
Lyophilized TB-500 is hygroscopic and should be kept dry before use. The usual storage recommendation for the solid is -20 °C, protected from light and moisture. Once dissolved, the peptide is less stable, and repeated freeze-thaw cycles can promote aggregation or degradation. Laboratories often divide a reconstituted solution into single-use aliquots and store them at -80 °C. Exact stability limits depend on buffer, pH, and concentration, so published data do not define a single universal condition.
Research peptides are typically supplied as a white to off-white lyophilised powder in a sealed vial. The dry solid is more stable than a solution and is normally kept refrigerated or frozen until use. Dissolution is usually done in water, phosphate-buffered saline or a similar aqueous medium, depending on the assay. Because the material is hygroscopic and easily contaminated, opening vials in a low-humidity environment and recording the lot number before use are standard laboratory practices.
Once in solution, short peptides are generally less stable than the dry powder, and repeated freeze-thaw cycles are a common cause of loss. Laboratory guidance usually calls for aliquoting on first dissolution and storing aliquots at -20 °C or below, away from light. Adsorption to plastic and glass surfaces can lower measured concentration, particularly at low concentrations, so container material and buffer choice can affect results. Visible cloudiness, colour change or unexpected precipitate is a signal to re-check the material.
== Particular oligomeric prodelphinidins == Prodelphinidin B3 (gallocatechin-(4α→8)-catechin) and prodelphinidin B9 (epigallocatechin-(4α→8)-catechin) can be isolated in beer. Prodelphinidin C2 (gallocatechin-(4α→8)-gallocatechin-(4α→8)-catechin) can be isolated in malt. The A-type proanthocyanidin epigallocatechin-(2β→7,4β→8)-epicatechin can be found in the leaves of Dioclea lasiophylla,
== Media portrayals == The Edge of Love, 2008 film with Thomas portrayed by Matthew Rhys and his wife, Caitlin, played by Sienna Miller. Set Fire to the Stars, 2014 film with Thomas portrayed by Celyn Jones and John Brinnin by Elijah Wood. Dominion, 2017 film with Thomas played by Rhys Ifans and Caitlin portrayed by Romola Garai.
According to the Qing Emperor Puyi, several locks were broken, nearby areas were ransacked, and the pearls and jade in the empress's crown were stolen by the end of his wedding ceremony. As part of an effort to crack down on this corruption, Puyi took inspiration from his tutor and close advisor, Reginald Johnston, and ordered an inventory of the Forbidden City's treasures. The Hall of Established Happiness was burned on the night of 26 June 1923, just when the emperor had ordered to carry out the inventory of one of the imperial warehouses. Puyi suspected it was arson to cover theft. Coupled with the fact that he had overheard conversations amongst the eunuchs that made him fear for his life, he evicted all but 50 to 100 eunuchs from the palace with the support of the Beiyang Army a month after the fire. Accounts regarding Sun's life henceforth differ. Some sources claim he remained an attendant to the Qing empress until the expulsion of the imperial family from the Forbidden City in 1924. He then followed them north and continued to serve in Manchukuo until the puppet state's collapse at the end of World War II, After which he became a caretaker of the Guanghua temple in Beijing, where he lived until his death, using the fact that he was one of the few eunuchs who were literate. Other sources state that the incident at The Hall of Established Happiness cut short Sun's career and forced him to leave.
Experts anticipate that future microfluidic-based innovations for directed evolution campaigns will be driven in the commercial space, resulting in more simple and less expensive methods and tools that can be applied to biotechnologically-relevant enzymes.
=== Regulation of indoor VOC emissions === In most countries, a separate definition of VOCs is used with regard to indoor air quality that comprises each organic chemical compound that can be measured as follows: adsorption from air on Tenax TA, thermal desorption, gas chromatographic separation over a 100% nonpolar column (dimethylpolysiloxane). VOC (volatile organic compounds) are all compounds that appear in the gas chromatogram between and including n-hexane and n-hexadecane. Compounds appearing earlier are called VVOC (very volatile organic compounds); compounds appearing later are called SVOC (semi-volatile organic compounds). France, Germany (AgBB/DIBt), Belgium, Norway (TEK regulation) and Italy (CAM Edilizia) have enacted regulations to limit VOC emissions from commercial products. European industry has developed numerous voluntary ecolabels and rating systems, such as EMICODE, M1, Blue Angel, GuT (textile floor coverings), Nordic Swan Ecolabel, EU Ecolabel, and Indoor Air Comfort. In the United States, several standards exist; California Standard CDPH Section 01350 is the most common one. These regulations and standards changed the marketplace, leading to an increasing number of low-emitting products.
Sources: en.wikipedia.org
==== Juan Alberto Kessel Linares and Viñas Alonso arrested ==== On July 4, 2025, agents from the State Security Unit issued summons to Acting Grand Mater Kessel Linares and Acting Grand Secretary Víctor Bravo Cabañas at the Picota Police Station, where they were again officially arrested by Lieutenant Colonel Kenia María Morales Larrea, but they were later released with warning notices. Filema Duarte called a special session of the High Chamber to occur on July 6. Many Cuban Freemasons considered this an illegal act, because they had voted him out of office, and believed that he did not have the authority to call sessions. After they were released, Kessel Linares and Bravo Cabañas both posted to Facebook that they were concerned about the intimidation tactics used by the government, and called for a peaceful demonstration on July 6.
=== Thailand === In Thailand, postgraduate medical training is monitored by the Medical Council of Thailand (TMC) and conducted by their respective "Royal Colleges". Thailand has a significant issue with an imbalance of medical personnel between Bangkok and the remaining 76 provinces. As a primate city, the majority of specialists wish to remain in Bangkok after training. Each year, the TMC outlines the requirements for application to a certain specialty, depending on the needs of the country for staff within that field. Specialities are therefore classified into tiers depending on national demand. The duration spent in the national internship program depends on the specialty the graduate wishes to study. Specialties classified as 'lacking' may require only one year of internship, whilst more competitive specialties often require the full three-year duration of internship to meet the application criteria. Fields classified as 'severely lacking' may not require internship training at all. Application to residency may be done on contract with a government hospital or without a contract, namely 'free-training'. Government hospitals may sign contracts to sponsor residency training for specialist doctors they require. In these cases, the duration for internship required in more popular fields may be reduced. For example, a residency in internal medicine requires three years of internship if applying without contract, but is reduced to two years if applying under contract.
Analyte ions are formed at ambient pressure during Penning and chemical ionization. The mass spectrometry analysis, however, takes place at high vacuum condition. Therefore, ions entering the mass spectrometer, first go through a source - to - analyzer interface (vacuum interface), which was designed in order to bridge the atmospheric pressure region to the mass spectrometer vacuum. It also minimizes spectrometer contamination. In the original JEOL atmospheric pressure interface used for DART, ions are directed to the ion guide through (outer) і and (inner) іі skimmer orifices by applying a slight potential difference between them: orifice і : 20 V and orifice іі : 5 V. The alignment of the two orifices is staggered to trap neutral contamination and protect the high-vacuum region. Charged species (ions) are guided to the second orifice through an intermediate cylindrical electrode ("ring lens"), but neutral molecules travel in a straight pathway and are thus blocked from entering the ion guide. The neutral contamination is then removed by the pump. The DART source can be operated in surface desorption mode or transmission mode. In the ordinary surface desorption mode, the sample is positioned in a way, which enables the reactive DART reagent ion stream to flow on to the surface while allowing the flow of desorbed analyte ions into interface. Therefore, this mode requires that the gas stream grazes the sample surface and does not block gas flow to the mass spectrometer sampling orifice.
==== Down syndrome ==== Trisomy 21 or Down syndrome is the most common human chromosomal anomaly arising from abnormal chromosomal segregation in meiosis. The condition can occur during anaphase in meiosis(I) marking oocyte maturation before ovulation and/or during anaphase in meiosis (II) signifying fertilization. Metabolic impact during these stages is furthered by low vitamin B12. Methylation of homocysteine to methionine is affected, primarily by the (MTRR):c.66A>G polymorphism. Chronic homocysteine elevation increases s-adenosyl-L-homocysteine levels, consequently inhibiting methyltransferase activity and promoting DNA hypomethylation. Mothers homozygous for this mutation (GG phenotype) are at a greater risk of having a child with down syndrome compared to heterozygotes (GA phenotype). Geographically, Irish populations are more likely to be homogenous whilst north American populations are commonly heterogeneous, resulting in a greater incidence of the polymorphism in the former group. The homozygous mutant allele promotes DNA hypomethylation and meiotic non-disjunction, increasing the risk of down syndrome. This polymorphism correlates to a 2.5 fold risk increase independently and a 4 fold increase in risk when co-expressed with the 677C>T MTHFR mutation. Combination with the MTR2756A>G genetic polymorphism further elevates down syndrome risk.
After the polymerisation of the separating gel, the alcohol is discarded and the residual alcohol is removed with filter paper. After addition of APS and TEMED to the stacking gel solution, it is poured on top of the solid separation gel. Afterwards, a suitable sample comb is inserted between the glass plates without creating bubbles. The sample comb is carefully pulled out after polymerisation, leaving pockets for the sample application. For later use of proteins for protein sequencing, the gels are often prepared the day before electrophoresis to reduce reactions of unpolymerised acrylamide with cysteines in proteins. By using a gradient mixer, gradient gels with a gradient of acrylamide (usually from 4 to 12%) can be cast, which have a larger separation range of the molecular masses. Commercial gel systems (so-called pre-cast gels) usually use the buffer substance Bis-tris methane with a pH value between 6.4 and 7.2 both in the stacking gel and in the separating gel. These gels are delivered cast and ready-to-use. Since they use only one buffer (continuous gel electrophoresis) and have a nearly neutral pH, they can be stored for several weeks. The more neutral pH slows the hydrolysis and thus the decomposition of the polyacrylamide. Furthermore, there are fewer acrylamide-modified cysteines in the proteins. Due to the constant pH in collecting and separating gel there is no stacking effect. Proteins in BisTris gels can not be stained with ruthenium complexes.
Sources: en.wikipedia.org
=== Books === Chromatographic Determination of Molecular Interactions (1994) ISBN 9780849344374 Physicochemical and Biomimetic Properties in Drug Discovery: Chromatographic Techniques for Lead Optimization (2014) ISBN 9781118152126 Separation Methods in Drug Synthesis and Purification (2020) ISBN 9780444640703
International law experts argued that the operation may have violated international law. On 3 January 2026, United Nations Spokesperson Stéphane Dujarric issued a statement that said the UN Secretary-General António Guterres was "deeply alarmed by the recent escalation in Venezuela" and that United States' military action "has potential worrying implications for the region". Lawyer Geoffrey Robertson stated that the strike on Venezuela was contrary to Article 2(4) of the UN Charter and qualifies as a crime of aggression under international law. Elvira Domínguez-Redondo, professor of international law at Kingston University, also stated the strike was an act of aggression and that it could only have been lawful if it had authorization by a United Nations Security Council resolution, or was justified as "self-defense", but she added that there was "no evidence whatsoever" to support either condition. Ben Saul, a UN special rapporteur and professor of international law, condemned "the US's illegal aggression against Venezuela and the illegal abduction of its leader and his wife" and called on Trump to be investigated and impeached. Professor of international law Michael N. Schmitt, law professor Ryan Goodman and Tess Bridgeman concluded that the operation against Venezuela "amounts to a severe breach of foundational principles of international law". Professor of law Ziyad Motala described the "intervention in Venezuela to abduct President Nicolás Maduro" as "international vandalism, plain and unadorned".
=== Food production === Nisin is used in processed cheese, meats, beverages, etc. during production to extend shelf life by suppressing Gram-positive spoilage and pathogenic bacteria. In foods, it is common to use nisin at levels ranging from ~1-25 ppm, depending on the food type and regulatory approval. As a food additive, nisin has an E number of E234. Growing consumer demand for natural preservatives has increased interest in nisin as a clean-label solution.
Vitamin C can be produced from glucose by two main routes. The no longer used Reichstein process, developed in the 1930s, used a single fermentation followed by a purely chemical route. The modern two-step fermentation process, originally developed in China in the 1960s, uses additional fermentation to replace part of the later chemical stages. The Reichstein process and the modern two-step fermentation processes both use glucose as the starting material, convert that to sorbitol, and then to sorbose using fermentation. The two-step fermentation process then converts sorbose to 2-keto-l-gulonic acid (KGA) through another fermentation step, avoiding an extra intermediate. Both processes yield approximately 60% vitamin C from the glucose starting point. Researchers are exploring means for one-step fermentation. China produces about 70% of the global vitamin C market. The rest is split among European Union, India and North America. The global market was expected to exceed 141 thousand metric tons in 2024. Cost per metric ton (1000 kg) in US dollars was $2,220 in Shanghai, $2,850 in Hamburg and $3,490 in the US.
This is thought to be helpful in competitive and social situations to conceal motives. Specifically, diurnal animals often have darker sclera to protect the eyes from UV, especially in larger animals where more sclera is exposed. Melanin plays an important role in the pigmentation of the sclera in humans and other animals. Melanin pigment in the sclera is similar to the pigment in the skin and irises where it absorbs UV radiation to prevent deeper penetration and damage to the eyes. Nocturnal animals have larger eyes and pupils to maximize light, while diurnal animals have smaller eyes to enhance visual acuity in bright light. This leads to increasing trends of nocturnal animals having larger sclera and eyeballs overall while diurnal animals have smaller ones for daylight activities.
Sources: en.wikipedia.org
The leading proposal involves sequestration of monomeric actin, which would alter cytoskeletal turnover and cell movement. The actin-binding motif shared with the parent protein is central to that idea. Direct confirmation in whole organisms remains limited.
Very few controlled human studies focus on the seven-residue sequence itself. Most clinical data concern the full-length protein in cardiac or ophthalmic settings. Conclusions drawn for one form should not be assumed to transfer to the other.
Detection normally relies on reversed-phase liquid chromatography paired with mass spectrometry. Chromatographic retention time establishes the expected elution window, and the mass spectrum confirms the molecular ion. Immunoassays exist but can cross-react with related peptides.
Not necessarily. TB-500 is a commercial label that suppliers apply to synthetic peptides described as thymosin beta-4 or a fragment of it. Published research most often studies the full-length protein, so statements about one do not automatically transfer to the other.