The short version of prohibited list fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2025-09-20. Anything still debated is marked as such rather than presented as settled.
TB-500 is a synthetic heptapeptide with the sequence Ac-LKKTETQ. It corresponds to a short N-terminal region of thymosin beta-4, a 43-amino-acid protein found in many cell types. The fragment contains an actin-binding motif, which is one reason it appears in laboratory studies of cell migration and cytoskeletal dynamics. TB-500 is not the full-length protein and is produced as a research chemical rather than an approved therapeutic agent. Its molecular weight is approximately 889 Da.
Several names appear in scientific and commercial contexts for this peptide. The label TB-500 is informal and does not follow standard biochemical nomenclature. Research articles more often describe the compound as a thymosin beta-4 fragment, Tβ4 fragment, or by its sequence Ac-LKKTETQ. Confusing TB-500 with full-length thymosin beta-4 can lead to incorrect assumptions about activity because the fragment lacks the remaining residues of the parent protein. The relationship between fragment and parent protein remains an active area of study.
Regulatory status differs by country, but TB-500 is not an approved pharmaceutical in major jurisdictions. It is commonly sold as a research chemical for laboratory use, which places responsibility for identity and purity on the supplier and the laboratory. Published human data are limited, and most reports involve preclinical models or cell culture. Questions about whether the fragment mimics all actions of thymosin beta-4, and under which conditions, remain open. Independent verification of any material is therefore a practical requirement in research settings.
The seven-residue chain carries several polar and charged side chains, so it dissolves readily in water and in aqueous buffers near neutral pH. No cysteine is present, so disulphide formation is not a concern and reducing agents are unnecessary. Dilute ammonium hydroxide or acetonitrile-water mixtures are sometimes used for stock solutions when initial dissolution is slow. Strongly alkaline conditions and prolonged contact with oxidising agents are avoided because they can modify lysine-containing stretches, and haze in solution usually signals incomplete dissolution or aggregated material.
Identity and purity are checked with reversed-phase high-performance liquid chromatography, which separates the target sequence from truncated or deletion analogues, and with mass spectrometry, which confirms the expected molecular mass. Amino acid analysis and peptide mapping give orthogonal confirmation but are used less often outside specialist laboratories. Counter-ion content varies: material purified on trifluoroacetic acid gradients retains trifluoroacetate, and ion exchange can convert the salt form. Residual water and solvent are measured by Karl Fischer titration or thermogravimetric analysis, and any purity figure should be read together with the method used to obtain it.
Lyophilised peptide powders are hygroscopic, and the fragment absorbs atmospheric moisture when a vial is opened at room temperature. Weighing and aliquoting are normally done quickly in a dry environment, and stock solutions are divided into single-use portions before freezing. Repeated freeze-thaw cycles are avoided because they promote aggregation and can shift the measured content of a vial. These practices are general to synthetic peptides rather than unique to this sequence, but they matter more for short chains kept for long periods.
| Property | Value | Notes |
|---|---|---|
| Molecular formula | C38H68N10O14 | Calculated for the acetylated heptapeptide |
| Molecular weight | ~889 Da | Monoisotopic mass approximately 889.0 Da |
| Amino acid sequence | Ac-LKKTETQ | N-terminal acetylated seven-residue peptide |
| Appearance | White to off-white powder | Typically supplied as a lyophilized solid |
| Solubility class | Water-soluble | Peptides of this size generally dissolve in aqueous media |
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.
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.
Detection in biological samples relies on mass spectrometry, typically liquid chromatography coupled to tandem mass spectrometry after peptide extraction and enrichment. Intact peptides can also be confirmed by high-resolution mass measurement together with fragmentation data. Detection windows in urine are short because the peptide is degraded by proteases and cleared quickly, and concentrations are low. Many jurisdictions treat the compound as a prohibited substance in sport, grouped with peptide hormones and related factors, while it is not an approved therapeutic product. Identity and purity statements therefore rest on certificates of analysis, ideally issued by an independent laboratory.
Material is normally supplied as a lyophilised powder in a sealed vial. The powder is hygroscopic, so exposure to humid air leads to water uptake, caking and gradual loss of the fluffy texture that indicates a good freeze-dry. Vials are best kept sealed with desiccant, protected from light and stored cold. Letting a cold vial warm to room temperature before opening reduces condensation on the contents. Purity is normally reported from a chromatographic run, and that figure applies to the batch as tested rather than to the vial after repeated opening.
In February 2018, logistics mismanagement by DHL, which had been selected by KFC UK as their new delivery partner, caused a chicken shortage in the United Kingdom – KFC's largest market in Europe – forcing the company to temporarily close hundreds of restaurants around the country. KFC apologized by taking out adverts in British newspapers showing the company's initials rearranged to read "FCK", followed by an apology, which was well received. In November 2021, Finland's first KFC restaurant was opened at the Itis shopping center in Itäkeskus, Helsinki. A few days before the opening day, a tent had appeared in front of the restaurant, where a man who had kept his identity secret for a few days had stayed, and who on the opening day revealed himself to the public as a vegan activist defending animal rights. After trying to give his speech to those present, the security company carried him away. Even before the opening of the restaurant, in October, news of a controversy over the procurement of a broiler for food from Poland; the cause is mainly related to the risk of salmonella in broilers, which is a significant problem in Poland, whereas its prevalence in Finland is low. Following the 2022 Russian invasion of Ukraine, a number of companies have faced growing pressure to halt operations in Russia but have not yet done so. This includes KFC, which has over 1,000 outlets in Russia, more than any other Western fast food chain. However, within a few years, all Russian KFC restaurants were rebranded as "Rostic's".
=== Brand names === As of June 2017, clonidine is marketed under many brand names worldwide: Arkamin, Aruclonin, Atensina, Catapin, Catapres, Catapresan, Catapressan, Chianda, Chlofazoline, Chlophazolin, Clonid-Ophtal, Clonidin, Clonidina, Clonidinã, Clonidine, Clonidine hydrochloride, Clonidinhydrochlorid, Clonidini, Clonidinum, Clonigen, Clonistada, Clonnirit, Clophelinum, Dixarit, Duraclon, Edolglau, Haemiton, Hypodine, Hypolax, Iporel, Isoglaucon, Jenloga, Kapvay, Klofelino, Kochaniin, Lonid, Melzin, Menograine, Normopresan, Paracefan, Pinsanidine, Run Rui, and Winpress. It is marketed as a combination drug with chlortalidone as Arkamin-H, Bemplas, Catapres-DIU, and Clorpres, and in combination with bendroflumethiazide as Pertenso.
== Further reading == Beck, M. T.; Kauffman, G. B. (1985). "COS and C3S2: The Discovery and Chemistry of Two Important Inorganic Sulfur Compounds". Polyhedron. 4 (5): 775–781. doi:10.1016/S0277-5387(00)87025-4. J. Elliott Campbell; Jürgen Kesselmeier; Dan Yakir; Joe A. Berry; Philippe Peylin; Sauveur Belviso; Timo Vesala; Kadmiel Maseyk; Ulrike Seibt; Huilin Chen; Mary E. Whelan; Timothy W. Hilton; Stephen A. Montzka; Max B. Berkelhammer; Sinikka T. Lennartz; Le Kuai; Georg Wohlfahrt; Yuting Wang; Nicola J. Blake; Donald R. Blake; James Stinecipher; Ian Baker; Stephen Sitch (2017). "Assessing a New Clue to How Much Carbon Plants Take Up". EOS. 98. doi:10.1029/2017EO075313. hdl:10871/31921. Svoronos P. D. N.; Bruno T. J. (2002). "Carbonyl sulfide: A review of its chemistry and properties". Industrial & Engineering Chemistry Research. 41 (22): 5321–5336. doi:10.1021/ie020365n.
Rapid evolutionary divergence, along with the multiple and parallel loss of orthologs in some lineages, can give the false appearance of the emergence of a novel gene from scratch. Recent syntheses highlight both rapid progress and ongoing debates in de novo gene research, including challenges in identification, functional validation, and links to microproteins and random-peptide experiments.
Sources: en.wikipedia.org
He convened researchers from the diverse fields converging on this newly recognized family of receptors and proposed a unifying nomenclature. Springer described the first sequence relationships among family members and was the first to use an αβ nomenclature in which α subunits were named after their receptor, such as αL for LFA-1 and αM for Mac-1. However, because the meeting was focused on fibronectin, the fibronectin receptor was designated α5β1, conferring the β1 designation on the subunit that pairs with more α subunits than any other β subunit in the family. The ones discovered by Springer on white blood cells became the β2 integrins. Contributions by Springer, Hynes, and Ruoslahti to the integrin field were recognized by the 2022 Lasker Basic Medical Research Award.
== Plutonium-240 as an obstacle to nuclear weapons == 240Pu undergoes spontaneous fission at a small but significant rate (5.8×10−6%). The presence of 240Pu limits the plutonium's use in a nuclear bomb, because a neutron from spontaneous fission starts the chain reaction prematurely, causing an early release of energy that disperses the core before full implosion is reached. This prevents most of the core from participation in the chain reaction and reduces the bomb's yield. Plutonium consisting of more than about 90% 239Pu is called weapons-grade plutonium; plutonium from spent nuclear fuel from commercial power reactors generally contains at least 20% 240Pu and is called reactor-grade plutonium. However, modern nuclear weapons use fusion boosting, which mitigates the predetonation problem; if the pit can generate a nuclear weapon yield of even a fraction of a kiloton, which is enough to start deuterium–tritium fusion, the resulting burst of neutrons will fission enough plutonium to ensure a yield of tens of kilotons. Contamination due to 240Pu is the reason plutonium weapons must use the implosion method. Theoretically, pure 239Pu could be used in a gun-type bomb, but achieving this level of purity is prohibitively difficult. 240Pu contamination has proven a mixed blessing. While it created delays and headaches during the Manhattan Project because of the need to develop implosion technology, those same difficulties are a barrier to nuclear proliferation. Implosion bombs are also inherently more efficient and less prone to accidental detonation than are gun-type bombs.
=== Opposition === On March 13, 2012, over 100 environmental and civil society groups, including Friends of the Earth, the International Center for Technology Assessment, and the ETC Group, issued the manifesto The Principles for the Oversight of Synthetic Biology. This manifesto calls for a worldwide moratorium on the release and commercial use of synthetic organisms until more robust regulations and rigorous biosafety measures are established. The groups specifically call for an outright ban on the use of synthetic biology on the human genome or human microbiome. Richard Lewontin wrote that some of the safety tenets for oversight discussed in The Principles for the Oversight of Synthetic Biology are reasonable, but that the main problem with the recommendations in the manifesto is that "the public at large lacks the ability to enforce any meaningful realization of those recommendations".
Wendy Greengross (29 April 1925 – 10 October 2012); author of books on pastoral care and counselling, journalist, general practitioner and broadcaster. The Independent called her "a pioneering counsellor and one of the leading figures in fighting for equal rights for the disabled and the elderly"; went into broadcasting, joining BBC Radio 4 counselling programme If You Think You've Got Problems; also had her own television show on BBC1, Let's Talk it Over; father was mayor of Holborn, and brother Sir Alan Greengross (born 1929) was Conservative member of Greater London Council. Tony Greenstein (born December 1953) is a left-wing anti-fascist, anti-Zionist writer activist, whose father came from a rabbinical family. Author of The Fight Against Fascism in Brighton & the South Coast, Zionism: Antisemitism's twin in Jewish garb and Zionism During the Holocaust: Weaponising Memory in the Service of State and Nation. John Hajnal (born Hajnal-Kónyi; 26 November 1924 – 30 November 2008), was Hungarian-British academic in fields of mathematics and economics (statistics); author of numerous monographs and academic papers and a book on the inefficacy of the British education system “The student trap: A critique of university and sixth-form curricula”; best known for identifying, in landmark 1965 paper, the historical pattern of marriage of northwest Europe in which people married late and many adults remained single.
== Cause == Burns are caused by a variety of external sources classified as thermal (heat-related), chemical, electrical, and radiation. In the United States, the most common causes of burns are: fire or flame (44%), scalds (33%), hot objects (9%), electricity (4%), and chemicals (3%). Most (69%) burn injuries occur at home or at work (9%), and most are accidental, with 2% due to assault by another, and 1–2% resulting from a suicide attempt. These sources can cause inhalation injury to the airway and/or lungs, occurring in about 6%. Burn injuries occur more commonly among the poor. Smoking and alcoholism are other risk factors. Fire-related burns are generally more common in colder climates. Specific risk factors in the developing world include cooking with open fires or on the floor as well as developmental disabilities in children and chronic diseases in adults.
Sources: en.wikipedia.org
TB-500 is a synthetic heptapeptide corresponding to a fragment of thymosin beta-4. It is used in laboratory research and is not an approved drug.
No. Thymosin beta-4 is a 43-amino-acid protein, while TB-500 represents only a short N-terminal segment. The two should not be treated as interchangeable in experimental design.
It is often called a thymosin beta-4 fragment, Tβ4 fragment, or Ac-LKKTETQ. The name TB-500 is mainly a commercial or catalog label rather than a formal chemical name.
Divide it into single-use aliquots and hold them frozen at -20 °C or below, protected from light. Repeated thawing of one container is the main avoidable source of variability.