If you have been reading about LKKTETQ 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.
Last reviewed on 2026-01-17. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
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.
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.
| 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 |
TB-500 is a short synthetic peptide sold under a trade name rather than a systematic chemical name. Suppliers usually describe it as a fragment of thymosin beta-4 and ship it as a lyophilised powder intended for laboratory use. Because the label is commercial, the exact sequence attributed to it is not fully consistent across catalogues, and some listings present a seven-residue peptide while others describe related fragments of similar length. It is not an approved medicine in any major jurisdiction, and it is handled as a research chemical.
Thymosin beta-4 itself is a natural peptide of 43 residues found in many cell types and body fluids. Its best-characterised function is binding and sequestering actin monomers, which influences cytoskeletal dynamics. The sequence most often associated with TB-500, LKKTETQ, corresponds to part of that actin-binding region. A different fragment, Ac-SDKP, is also derived from the same parent peptide and is studied in its own right, which is one reason discussions of thymosin fragments can become confusing. The two are structurally distinct and are not interchangeable.
Interest in the fragment grew during the 1990s and 2000s, when it moved from laboratory work into sports and supplement markets. Anti-doping bodies added thymosin beta-4 fragments to prohibited lists, and a small number of adverse analytical findings have been reported in competition testing. Published controlled human trials remain scarce. Most mechanistic evidence comes from cell culture and animal models, and those studies examine endpoints such as cell migration, wound closure and inflammation markers. That evidence supports research interest but does not establish clinical benefit, and broad regenerative claims should be read as unverified.
Purity and identity are separate measurements and are often confused. Reverse-phase high-performance liquid chromatography, usually with ultraviolet detection near 214 nanometres, reports the share of total peak area belonging to the target compound. Mass spectrometry by electrospray or matrix-assisted laser desorption then checks whether the observed mass matches the expected sequence. Neither measurement alone shows that a vial holds the intended peptide. Peptide content, meaning the fraction of vial mass that is genuine peptide rather than counter-ion, water or residual acid, is reported separately and is frequently lower than the stated purity figure.
The regulatory position is broadly consistent across major jurisdictions: no thymosin beta-4 fragment is an approved medicine, and laboratory material is commonly labelled as not intended for human consumption. Anti-doping rules in sport list thymosin beta-4 and its fragments among prohibited peptide hormones. Because these products travel through research-chemical channels rather than pharmaceutical supply chains, quality varies considerably between vendors. Independent testing of identity, purity and sterility is the only dependable check, and a certificate of analysis describes one batch rather than a supplier's whole catalogue.
TB-500 is a catalogue name applied to a synthetic peptide related to thymosin beta-4, an actin-binding protein found in most mammalian cells. Suppliers do not use the label consistently: some describe it as the full 43-residue protein, others as a short fragment from the actin-binding region, and others as a related tetrapeptide. Because the name is commercial rather than chemical, two products sold under it may not contain the same molecule. This naming ambiguity is the first point to check in any description of the material.
The most frequently cited identity is a seven-residue fragment with the sequence LKKTETQ, taken from the actin-binding domain of the parent protein. A separate molecule, N-acetyl-seryl-aspartyl-lysyl-proline, often shortened to Ac-SDKP, derives from the same protein's N-terminal region and appears in overlapping literature. Reported molecular masses therefore differ between sources, and a mass value on its own does not establish which fragment is present. Confirmation requires a defined sequence rather than a single number.
Research interest in thymosin beta-4 fragments centres on actin sequestration, cell migration and tissue repair models. Most published work uses cultured cells or animal wound and cardiac preparations, and findings are generally described as preliminary. No fragment of this protein has been approved as a therapeutic product by major regulators. Reviews of the field note inconsistent dosing, delivery routes and outcome measures across studies, which complicates direct comparison. The material is best understood as a laboratory reagent with an active but unresolved research literature.
Dry peptide powder is commonly kept at −20 °C in a desiccated container away from light, a practice that limits moisture uptake and oxidation. Once dissolved, solutions are generally held at 2–8 °C for short periods or frozen at −20 °C or lower for longer storage, with repeated freeze-thaw cycles avoided. Hydrolysis and oxidation are the main degradation routes for peptides in solution, and both accelerate at higher temperature or extreme pH. Published stability data specific to TB-500 are limited, so shelf life should be treated as uncertain.
Identity and purity checks for peptide material typically combine reversed-phase high-performance liquid chromatography with mass measurement, since retention time alone cannot confirm a sequence. Mass measurement verifies the expected molecular mass within instrument tolerance, while chromatographic peak area provides a purity estimate. Anti-doping analysis of urine uses related but more sensitive workflows, sometimes after solid-phase extraction. For research material, batch documentation, certificate content, and independent testing are common points of scrutiny, because supply chains outside pharmaceutical regulation vary widely in the paperwork they provide.
Reconstitution of a lyophilized peptide is normally done with sterile water or a suitable buffer under aseptic conditions. Adding solvent down the vial wall and allowing gentle dissolution instead of vigorous vortexing reduces the chance of aggregation, which can lower the effective concentration of the resulting solution. Concentrated stocks are usually diluted into working buffer shortly before use. Because no standard preparation protocol exists for TB-500 specifically, laboratories adapt general peptide handling practice, and reported results may reflect differing preparation choices.
=== Importance === Calciseptine has been shown to specifically inhibit the L-type voltage-gated Ca2+ channels and was the first natural polypeptide discovered with this property. Specific polypeptide inhibitors of voltage-sensitive channels are important tools in research, and were already known for voltage-sensitive Na+ channels, both voltage-sensitive and Ca2+-activated K+ channels, and for N-type Ca2+-channels. Before calciseptine was sequenced and shown to be a specific L-type calcium channel inhibitor, no specific polypeptide inhibitors were known for this type of voltage-gated channels. Specific blockers of the L-type channel were small organic molecules like 1,4-dihydropyridines. It was suggested that polypeptide inhibitors could be found in snake venoms. Calciseptine confirmed this as it was shown to not only block the L-type channels specifically, but also to do this in exactly the same spot as the 1,4-dihydropyridines. After calciseptine, other polypeptides specifically blocking the L-type channels were found as well: FS2, C10S2C2 and S4C8.
In February 2024, Senator Scott Wiener introduced the Safe and Secure Innovation for Frontier Artificial Intelligence Models Act to the California legislature. The bill drew heavily on the Biden executive order and had the goal of reducing catastrophic risks by mandating safety tests for the most powerful AI models. If passed, the bill would have established a publicly-funded cloud computing cluster in California. Governor Gavin Newsom vetoed the bill in September 2024. The Artificial Intelligence Training Data Transparency Act (AB 2013) and Transparency in Frontier Artificial Intelligence Act (TFAIA) (SB 53) went into effect on January 1, 2026. In addition, the California AI Transparency Act will go into effect in August 2026. By signing TFAIA into law in September 2025, California became the first state to enact a statute specifically addressing the development of frontier AI models. The TFAIA protects whistleblowers who have reasonable cause to believe their employers are endangering lives or causing damages worth $1 billion. It also requires companies to publish their safety test results. The political action committee Parents & Kids Safe AI Coalition, funded by OpenAI, has been involved in efforts to establish legislation related to child safety and AI in California. In September 2024, Alameda County's Board of Supervisors approved a countywide policy for agency and department usage of generative artificial intelligence (GenAI) technology.
The diverse range of intrinsic activities of cyclotides also continues to hold promise for a wide range of applications in the agricultural fields against insects and nematodes, especially those from Clitoria ternatea.
Sources: en.wikipedia.org
== Mechanism of action == Thiamazole inhibits the enzyme thyroperoxidase, which normally acts in thyroid hormone synthesis by oxidizing the anion iodide (I−) to iodine (I2), hypoiodous acid (HOI), and enzyme linked hypoiodate (EOI), facilitating iodine's addition to tyrosine residues on the hormone precursor thyroglobulin, a necessary step in the synthesis of triiodothyronine (T3) and thyroxine (T4). It does not inhibit the action of the sodium-dependent iodide transporter located on follicular cells' basolateral membranes. Inhibition of this step requires competitive inhibitors such as perchlorate and thiocyanate. A study has shown that it modulates secretion of CXCL10.
=== Black local authorities === In the immediate aftermath of the 3 September riots, it was already evident that members of black local councils had been targeted; initial figures suggested that at least three councillors had been killed and the homes of several others subjected to arson attacks. Later analyses showed that attacks on property had, similarly, targeted government buildings and shops, vehicles, and houses owned by councillors and, to a lesser extent, by local black policemen. This pattern was maintained in later months. The government was forced to relocate Vaal councillors to a secure complex on the outskirts of Sebokeng, and large numbers of councillors nationwide (257 between September 1984 and May 1985) resigned in fear. By mid-1985, Minister of Constitutional Development Chris Heunis was forced to begin appointing white civil servants to the councils for a lack of black applicants, and in June of that year it was estimated that fewer than six local councils remained operative in the entire country. Combined with rent boycotts, this brought public services to a halt in many townships. Similarly, black policemen – some employed by the Security Branch – were targeted. According to government figures, about 500 houses belonging to black policemen were burned down between March 1984 and November 1985.
=== Acceptance === Individuals with dwarfism often face prejudice and stereotypes. Research by Klein (2019) has demonstrated that awareness of the stigmatization of this group can promote full participation in society. The research by Green and Pinter (2018) in the field of humor and social psychology can provide insights to reduce stereotypes and promote a more objective perception.
Sources: en.wikipedia.org
Affinity towards An(III) over Ln(III) Good An(III) back-extraction to enable solvent recycling Good solubility in a proper diluent CHON compliance to reduce secondary waste Fast complexation kinetics Hydrodynamic stability to prevent third phase and precipitates formation during extraction process Chemical and radiolytic stability to prevent solvent degradation Research on advanced reprocessing of spent nuclear fuel moves on by developing process optimization studies and designing new potential lipophilic and hydrophilic extracting agents that fulfill these industrial requirements.
A classic example is two seeds of genetically identical corn, one placed in a temperate climate and one in an arid climate (lacking sufficient waterfall or rain). While the average height the two corn stalks could grow to is genetically determined, the one in the arid climate only grows to half the height of the one in the temperate climate due to lack of water and nutrients in its environment.
The former republics were transformed into the British colonies of the Transvaal and Orange River, and in 1910 were merged with the Natal and Cape Colonies to form the Union of South Africa, a self-governing colony within the British Empire. British expeditionary efforts were aided significantly by colonial forces from the Cape Colony, the Natal, Rhodesia, and many volunteers from the British Empire. Native African recruits contributed increasingly to the British effort. International public opinion was sympathetic to the Boers and hostile to the British. Even within the UK, there existed significant opposition to the war. As a result, the Boer cause attracted volunteers from neutral countries, including the German Empire, the United States, Russia and parts of the British Empire, such as Australia and Ireland. Some consider the war the beginning of questioning the British Empire's global dominance, due to the war's surprising duration and unforeseen losses suffered by the British. A trial for British war crimes, including the killings of civilians and prisoners of war, was opened in January 1902. The war had a lasting effect on the region and on British domestic politics.
=== Other === An engineer replaced a woodpecker-damaged feed horn of a high-power microwave antenna, a 15-meter dish at an Earth station of a television network, using a cherry picker. After finishing, he sent his technician to power up the transmitter, and attempted to lower the cherry picker down. The engine failed and the engineer was stuck next to the antenna, outside of its main lobe but well within the first sidelobe. The technician, unaware that the engineer was still close to the antenna, powered it up. The engineer was exposed to an intense microwave field for about three minutes, until the error was realized. There were no immediate symptoms; the next morning the engineer detected blood and solid matter in his urine, and visited a doctor, who found blood in stool and massive bowel adhesions. The engineer's medical problems lasted for many years.
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.
Sealed, dry and protected from light at reduced temperature is the usual laboratory convention. Allowing a cold vial to reach room temperature before opening limits condensation. Repeated opening exposes the powder to moisture and should be minimised.