A practical reference on actin binding: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
This page was last updated on 2026-02-09 and is reviewed periodically as new material appears.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Water content | Low in freshly lyophilised material | Rises after repeated opening of the same vial |
| Solution stability | Lower than powder stability | Frozen aliquots are preferred over repeated thawing |
| Purity assessment | Reversed-phase HPLC with UV detection | Peak-area percentage excludes salts and water |
| Salt form | Often the trifluoroacetate salt | Retained from acidic purification gradients |
| Light sensitivity | Not strongly photoreactive | Dark storage still advised for long-term keeping |
TB-500 is a synthetic seven-residue peptide whose sequence, LKKTETQ, matches the N-terminal actin-binding region of thymosin beta-4. It is usually supplied in an N-terminally acetylated form, a modification that blocks the free amino terminus and can influence behavior in solution. In the research literature the same sequence appears under several names, including thymosin beta-4 fragment and shortened thymosin beta-4. Because it is a short peptide rather than the full 43-residue parent protein, its measured properties differ from those reported for thymosin beta-4 as a whole, and the two are not interchangeable in experimental design.
Thymosin beta-4 itself is a small, widely expressed protein that sequesters monomeric actin and participates in cell migration, angiogenesis, and tissue repair. Researchers have examined the shortened fragment as a possible mimic of some of these activities, reasoning that the actin-binding motif lies within the first few residues. Binding to monomeric actin has been observed in cell-free systems. Whether the fragment reproduces the broader effects of the full protein in living tissue remains an open question, and findings from animal models are frequently cited without a clear bridge to human physiology.
Discussion of TB-500 appears in several distinct literatures that rarely cite one another. Peer-reviewed studies usually describe in vitro assays or small animal experiments and are cautious about extrapolation. Veterinary and sports communities circulate anecdotal reports with limited methodological detail. Commercial listings add a third layer, often using the name interchangeably with thymosin beta-4 even though the two molecules differ in size and sequence. Regulatory status varies by country, and the compound is not a licensed medicine in most jurisdictions, so readers comparing sources should check which molecule and which purity each source actually describes.
Published research on the intact protein is substantial, covering actin regulation, cell migration, and wound models. Research using the heptapeptide fragment specifically is far smaller, and much of the circulating material originates in supplier documentation rather than peer-reviewed reports. Where fragment studies do exist, they often employ different sequences, chain lengths, or terminal modifications, which complicates direct comparison across papers. Readers encountering claims about TB-500 should therefore separate evidence about thymosin beta-4 from evidence about the fragment itself.
Discussion of the compound frequently appears alongside other short peptides described as fragments of larger proteins. That grouping is convenient but can be misleading, because fragment length, charge, and modification state determine how a peptide behaves in solution and in any experimental system. A seven-residue acetylated peptide and a full-length protein differ in mass by roughly an order of magnitude, and they cannot be assumed to share distribution or binding properties. Precision about which molecule is under discussion is the single most useful step when reading such material.
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.
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.
His rare non-comedic film roles include two collaborations with Andre Gregory and Louis Malle: the semi-autobiographical dialogue My Dinner with Andre, and a combined production-and-backstage-drama of Uncle Vanya titled Vanya on 42nd Street. Shawn quite often appears on television, where he has appeared in many genres and series. He has had recurring roles as the Grand Nagus Zek on Star Trek: Deep Space Nine, Stuart Best on Murphy Brown, Jeff Engels on The Cosby Show, Dr. Howard Stiles on Crossing Jordan, Arnie Ross on Taxi, Charles Lester on both The Good Wife and The Good Fight, a reprisal of his role as Mr. Hall on Clueless (based on the film), and Father Frank Ignatius on Evil. He appeared in the 1985 music video for Chaka Khan's "This Is My Night". On February 4, 2010, Shawn appeared as Alan Rubin on The Daily Show with Jon Stewart. A Master Builder opened in New York City in June 2014. In 2018, he joined the cast of Young Sheldon in the recurring role of Meemaw's boyfriend and Sheldon's physics professor, Dr. John Sturgis. Shawn starred in Woody Allen's 2020 film Rifkin's Festival, set in San Sebastián, Spain. Shawn was honored in 2005 with the PEN/Laura Pels International Foundation for Theater Award as a Master American Dramatist.
==== January 2024 ==== On 2 January, Israel conducted an airstrike in the Dahieh neighborhood of Beirut, resulting in the assassination of Saleh al-Arouri, the deputy chairman of the Hamas political bureau, and the death of six other members. Al-Arouri was also responsible for the expansion of Hamas's activities in the Israeli-occupied West Bank, including attacks on Israelis. The assassination occurred one day before Hezbollah commemorated the fourth anniversary of the assassination of senior Iranian military commander Qasem Soleimani. On 6 January, Hezbollah launched approximately 40 rockets into northern Israel, describing it as an "initial response" to al-Arouri's killing. According to Israel, the rockets targeted a Air traffic Control Base near Mount Meron, causing significant damage to it. On 8 January, Israel assassinated Wissam al-Tawil, the deputy commander of Hezbollah's Redwan Force, whom it accused of carrying out the attack on Meron airbase two days earlier. In response to al-Tawil's killing, Hezbollah launched a drone attack on Israel's Northern Command headquarters in Safed on the following day, situated approximately 20 kilometres (12 mi) from the border. Ali Hussein Barji, the commander of Hezbollah's aerial forces in southern Lebanon who was reportedly responsible for the attack, was killed by an airstrike, according to Israel, alongside three other Hezbollah members, in Khirbet Selm shortly before al-Tawil's funeral began. However, Hezbollah denied that Barji was killed.
The back-end of the nuclear fuel cycle, mostly spent fuel rods, contains fission products that emit beta and gamma radiation, and actinides that emit alpha particles, such as uranium-234 (half-life 245 thousand years), neptunium-237 (2.144 million years), plutonium-238 (87.7 years) and americium-241 (432 years), and even sometimes some neutron emitters such as californium (half-life of 898 years for californium-251). These isotopes are formed in nuclear reactors. It is important to distinguish the processing of uranium to make fuel from the reprocessing of used fuel. Used fuel contains the highly radioactive products of fission (see high-level waste below). Many of these are neutron absorbers, called neutron poisons in this context. These eventually build up to a level where they absorb so many neutrons that the chain reaction stops, even with the control rods completely removed from a reactor. At that point, the fuel has to be replaced in the reactor with fresh fuel, even though there is still a substantial quantity of uranium-235 and plutonium present. In the United States, this used fuel is usually "stored", while in other countries such as Russia, the United Kingdom, France, Japan, and India, the fuel is reprocessed to remove the fission products, and the fuel can then be re-used. The fission products removed from the fuel are a concentrated form of high-level waste as are the chemicals used in the process. While most countries reprocess the fuel carrying out single plutonium cycles, India is planning multiple plutonium recycling schemes and Russia pursues closed cycle.
Sources: en.wikipedia.org
=== ICD-11 === Fibromyalgia is not listed as a code in the ICD-11. "Fibromyalgia syndrome" is listed as an inclusion in the ICD-11 code of "Chronic widespread pain" (CWP) (code MG30.01). (No other signs or symptoms of fibromyalgia are mentioned.)
=== Fatty acid biosynthesis === The precursor for fatty acids is acetyl-CoA and it occurs in the cytosol of the cell. The overall net reaction, using palmitate (16:0) as a model substrate is: 8 Acetyl-coA + 7 ATP + 14 NADPH + 6H+ → palmitate + 14 NADP+ + 6H2O + 7ADP + 7P¡
=== Station reconstruction plans in the 2020s === In April 2021, MTA officials under governor Andrew Cuomo proposed two options to reconstruct the Penn Station building under Madison Square Garden, to be financed by the development of 10 new office and residential towers in the surrounding neighborhood: one retained the existing two-level concourse, the other envisioned a taller single-level concourse with a glass atrium in the former midblock taxiway. Opponents alleged the tower development would provide a disproportionate tax advantage to real-estate firm Vornado Realty Trust. In November 2021, after Cuomo resigned, governor Kathy Hochul attempted to advance reconstruction by selecting the one-level plan and slightly reducing the size of the office tower development, and the administration announced FXCollaborative as designer in September 2022 with the assistance of John McAslan. But in February 2023, Vornado declared it would no longer invest in new office space due to lack of demand following the COVID-19 pandemic, and that June Hochul announced Penn Station reconstruction would be "decoupled" from any office tower development. In April 2025, transportation secretary Sean Duffy announced the U.S. Department of Transportation would take over reconstruction from the MTA, and he selected former New York City Transit Authority president Andy Byford to lead the effort. In response, Hochul said that New York State would no longer pay $1.3 billion that it had previously expected to contribute.
Sources: en.wikipedia.org
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.
Mass spectrometry confirms identity, because the measured mass is compared with the value expected from the sequence. Chromatography mainly reports how much of the material elutes as the target peak.
It usually describes the share of the chromatographic peak area recorded at a set wavelength. Salts, residual water, and solvent are excluded from that number, so it is not the same as mass fraction.
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.