If you have been reading about prohibited list and want a single page that covers the useful parts, this is it: definitions, context, how it is studied, and the questions that come up repeatedly.
Updated 2026-02-28. Numbers and descriptions here follow the published literature rather than marketing material.
TB-500 is a synthetic peptide whose sequence corresponds to a short fragment near the N-terminus of thymosin beta-4, a small protein present in most mammalian cells. The fragment is commonly cited as containing the actin-binding region of the parent molecule, which is why it appears in laboratory work on cell migration and tissue repair. Suppliers distribute it as a lyophilised powder intended for research use. Its identity is defined by amino acid sequence and by the presence of an acetyl group on the N-terminal residue.
Full-length thymosin beta-4 consists of roughly forty-three amino acids and ranks among the more abundant small proteins in the cytoplasm. The fragment is much shorter, so it cannot reproduce every function attributed to the intact molecule. In cell culture, short actin-binding motifs can interfere with filament dynamics and cell movement, but such observations come from controlled experiments rather than from whole-animal work. Whether a truncated fragment produces the same effects as the parent protein remains an open question.
Interest in the peptide grew during the 2000s and 2010s, when studies of tendon and ligament injuries in horses reported changes in lesion size after treatment. Those reports circulated widely outside the scientific literature and shaped much of the current online discussion. Subsequent reviews noted inconsistent study design, small groups, and a shortage of independent replication. Popular descriptions often blur the line between the fragment, the complete protein, and unrelated growth factors, which complicates comparisons across sources.
Laboratory work on thymosin beta-4 describes binding to monomeric actin and effects on cell migration, angiogenesis, and inflammatory signaling in cultured cells. Animal models have examined skin, corneal, and cardiac repair after injury, with outcomes reported mainly in preclinical literature. Most of that evidence concerns the parent protein rather than preparations labelled TB-500, so extrapolation from animal findings to a specific commercial product remains uncertain. Whether the two behave identically in living systems has not been established in controlled human studies.
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 |
|---|---|---|
| Generic designation | Synthetic thymosin beta-4 N-terminal fragment | Peptide nomenclature varies by supplier |
| Peptide length | Approximately 17 amino acid residues | Reported length sometimes differs between sources |
| N-terminal modification | Acetyl group | Affects mass and chromatographic behaviour |
| Compound class | Small synthetic peptide | Not a small-molecule drug |
| Common synonyms | TB4 fragment; thymosin beta-4 fragment | Naming is inconsistent in popular media |
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.
Once dissolved, the peptide is far less stable than the dry powder. Aqueous solutions are subject to hydrolysis, oxidation at susceptible residues and gradual loss of material through adsorption onto glass and plastic surfaces. Terminal glutamine can cyclise under some conditions, producing a related species that complicates purity assessment. Dilute solutions tend to lose a larger fraction of material to surfaces than concentrated ones. Buffers, pH and ionic strength all influence the rate of change, so stability figures are only meaningful when those parameters are stated alongside the storage interval.
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.
== Science and technology == 4 Vesta, an asteroid Vesta family, group of asteroids that includes 4 Vesta Vesta (rocket), a French sounding rocket The Vesta parallel file system, a precursor of IBM's GPFS Vesta (software configuration management) (developed 1993), advanced configuration management system released by Compaq Vesta, a genus of flowering plant in the family Araceae Vesta longifolia, sole species of the genus Vesta Vestas (founded 1945), Danish manufacturer of wind turbines
The first step in testing a new treatment in humans. These studies test the best way to give a new treatment (for example, by mouth, intravenous infusion, or injection) and the best dose. The dose is usually increased a little at a time in order to find the highest dose that does not cause harmful side effects. Because little is known about the possible risks and benefits of the treatments being tested, phase I trials usually include only a small number of patients who have not been helped by other treatments. (NCI) Initial studies to determine the metabolism and pharmacologic actions of drugs in humans, the side effects associated with increasing doses, and to gain early evidence of effectiveness; may include healthy participants and/or patients. (NLM) Phase 1 includes the initial introduction of an investigational new drug into humans. Phase 1 studies are typically closely monitored and may be conducted in patients or normal volunteer subjects. These studies are designed to determine the metabolism and pharmacologic actions of the drug in humans, the side effects associated with increasing doses, and, if possible, to gain early evidence on effectiveness. During Phase 1, sufficient information about the drug's pharmacokinetics and pharmacological effects should be obtained to permit the design of well-controlled, scientifically valid, Phase 2 studies. The total number of subjects and patients included in Phase 1 studies varies with the drug, but is generally in the range of 20 to 80.
=== Allegations and lawsuit against the Mirror Group === In October 1991, Galloway tabled a motion in the House of Commons expressing concern at the allegations against news publisher Mirror Group Newspapers put forward in Seymour Hersh's recently published book, The Samson Option: Israel's Nuclear Arsenal and American Foreign Policy. Hersh alleged that the Daily Mirror's foreign editor, Nicholas Davies, was involved in weapons sales to Iran and had given the whereabouts of Mordechai Vanunu to Mossad. Mossad sought to capture Vanunu due to his role as a whistleblower of Israeli nuclear operations, and later "lured [him] out of Britain to Italy", where he "was kidnapped, drugged and returned to Israel". Galloway's motion also called upon Mirror Group's owner, Robert Maxwell, to appoint a tribunal to investigate the allegations and the potential involvement of foreign intelligence in the publishing group. As the motion was signed under parliamentary privilege, other news outlets could report on it without worrying about legal repercussion, as Maxwell was known for litigiousness. Following this, the Daily Mirror published a "vitriolic" front-page editorial against Galloway, accusing him of abusing parliamentary privilege and of being motivated by links to anti-Israel terrorist groups. Galloway sued for libel and was awarded a public apology and substantial undisclosed damages from the Mirror Group.
=== Quantification === The digested fragments are then separated by polyacrylamide gel electrophoresis with the expected appearance of bands corresponding to a single large undigested fragment, and multiple smaller bands corresponding to digested fragments. Quantitative amount of DNA in these bands can be determined with a device such as a phosphoimager, after which the methylation percentage of the original sample can be calculated by:
Sources: en.wikipedia.org
If the aqueous solution is saturated with a given salt solute, any additional such salt precipitates out of the solution. In the more general Brønsted–Lowry acid–base theory (1923), a base is a substance that can accept hydrogen cations (H+)—otherwise known as protons. This does include aqueous hydroxides since OH− does react with H+ to form water, so that Arrhenius bases are a subset of Brønsted bases. However, there are also other Brønsted bases which accept protons, such as aqueous solutions of ammonia (NH3) or its organic derivatives (amines). These bases do not contain a hydroxide ion but nevertheless react with water, resulting in an increase in the concentration of hydroxide ion. Also, some non-aqueous solvents contain Brønsted bases which react with solvated protons. For example, in liquid ammonia, NH2− is the basic ion species which accepts protons from NH4+, the acidic species in this solvent. G. N. Lewis realized that water, ammonia, and other bases can form a bond with a proton due to the unshared pair of electrons that the bases possess. In the Lewis theory, a base is an electron pair donor which can share a pair of electrons with an electron acceptor which is described as a Lewis acid. The Lewis theory is more general than the Brønsted model because the Lewis acid is not necessarily a proton, but can be another molecule (or ion) with a vacant low-lying orbital which can accept a pair of electrons. One notable example is boron trifluoride (BF3). Some other definitions of both bases and acids have been proposed in the past, but are not commonly used today.
=== Opposition: 1975–79 === Heseltine did not work easily with women as senior colleagues, as was shown by the difficulty experienced by Elinor Goodman in obtaining promotion from secretary to journalist at Campaign, and his reluctance to let Josephine Hart sit on the Haymarket Board. Heseltine fully expected to be sacked from the Shadow Cabinet by the new leader (as Peter Walker was at this time), but was retained, in part because Thatcher was impressed by his fierce opposition to Benn's Industry Bill, and partly because a senior figure, possibly Geoffrey Howe, argued for his retention. Heseltine first emerged as a platform orator at the Conservative National Council in March 1975, and then at the autumn conferences in 1975 and 1976 (where he likened Labour to a one-legged army marching "Left, left, left"). He dictated his speech ideas beforehand to his scriptwriters, who had to discard a good deal of unintelligible material. His reputation was derived not from any factual content or argument, but from the force and brio of his delivery – it was said of him that he could "find the party's clitoris". There was talk of his being appointed Party Chairman (in charge of the party organisation and of campaigning across the country) in place of Peter Thorneycroft. In the summer of 1975, Heseltine persuaded the Shadow Cabinet not to oppose the Labour Government's bailout of British Leyland because of the risk to marginal seats (including some Cowley workers in northern wards of his own Henley seat).
=== Imprinting === Molecular imprinting describes a process by which a host is constructed from small molecules using a suitable molecular species as a template. After construction, the template is removed leaving only the host. The template for host construction may be subtly different from the guest that the finished host binds to. In its simplest form, imprinting uses only steric interactions, but more complex systems also incorporate hydrogen bonding and other interactions to improve binding strength and specificity.
== Research == Hong's research focuses on elucidating the structure, dynamics and mechanism of membrane proteins using ssNMR. She is particularly known for her in-depth study of the Matrix-2 (M2) proteins of influenza A viruses, which are responsible for all flu pandemics in history. M2 is an acid-activated proton channel and a membrane scission protein of the influenza virus. Hong's ssNMR studies have provided insights into the proton-conduction mechanism of this channel, by quantifying the proton transfer rates and equilibria between water and the proton-selective histidine residue. She showed that the antiviral drug amantadine inhibits proton conduction by direct occlusion of the channel pore. She determined the cholesterol-binding structure of the M2 protein, which sheds light on how cholesterol mediates M2's membrane scission function. In 2020 she determined both the influenza B M2 protein structure and the SARS-CoV-2 envelope protein structure, the latter in rapid response to COVID-19. The 1.5 Å BM2 structures in the closed and open states revealed different activation mechanisms of BM2 compared to influenza AM2. The 2.1 Å SARS-CoV-2 envelope protein structure forms the basis for antiviral drug design. Other membrane proteins that Hong's group has studied include β-hairpin antimicrobial peptides, channel-forming colicins, and viral fusion proteins. She determined the structure of the membrane toroidal pores formed by the antimicrobial peptide protegrin-1, which explained the membrane-disruptive mechanism of this peptide.
In 1980, Lady Hamilton Fairley, the widow of Sir Neil Hamilton Fairley began a campaign to have a memorial to Florey in London. The Premier of South Australia, David Tonkin, agreed to provide South Australian marble for a memorial stone. South Australian sculptor Paul Trappe was commissioned to engrave it from a design by John Peters. The 60-by-90-centimetre (24 by 35 in) stone was flown to London by the Royal Australian Air Force, and unveiled by Lady (Margaret) Florey on 2 November 1981. The inscription on the stone reads:
Sources: en.wikipedia.org
It is a synthetic peptide based on a short sequence near the start of thymosin beta-4. It is supplied as a research chemical rather than as a licensed pharmaceutical product.
No. Thymosin beta-4 is the full-length protein of about forty-three amino acids, while the fragment covers only its beginning. The two are related but are not interchangeable in experimental or analytical terms.
The label is a catalogue designation that became common in non-technical discussion. Scientific papers usually refer to the fragment by sequence or as a thymosin beta-4 N-terminal peptide.
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.