The short version of Ac-LKKTETQ fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2026-01-18. Anything still debated is marked as such rather than presented as settled.
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.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Appearance | White to off-white lyophilized powder | Typical form for short synthetic peptides |
| Solubility class | Freely soluble in water and aqueous buffer | Dissolution aided by gentle mixing, not vigorous shaking |
| Typical storage temperature | −20 °C, desiccated | −80 °C used for long-term holding |
| Common analytical method | Reverse-phase HPLC with UV detection near 214 nm | Identity confirmed separately by mass spectrometry |
| Common synonyms | Thymosin beta-4 fragment; TB4 fragment | Naming varies between suppliers and publications |
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.
Thymosin beta-4 is a 43-residue actin-binding protein found in most mammalian cell types, where it participates in cytoskeletal regulation and cell migration. TB-500 represents only a short fragment of that protein and does not include the remaining residues. Whether the isolated fragment reproduces the full range of activities reported for the intact protein remains an open question. Researchers commonly treat the two as related but distinct entities when comparing results.
Published work involving this sequence spans actin-binding assays, cell-migration studies, wound-healing models, and cardiovascular or musculoskeletal experiments. Much of the biological rationale derives from in vitro systems and animal models, and the number of controlled human studies is small. Reported outcomes vary across preparations, doses, and routes, which complicates comparison between studies. Reviews generally describe the evidence base as preliminary rather than settled. Mechanistic explanations are often proposed by analogy to the parent protein rather than demonstrated directly.
TB-500 is a synthetic seven-amino-acid peptide with the sequence LKKTETQ, corresponding to residues 17 through 23 of the protein thymosin beta-4. The N-terminus is typically acetylated in the described form, giving a monoisotopic mass near 888.5 Da and an average mass of about 889 Da. The designation TB-500 is a catalogue label rather than a formal chemical name, and the same sequence appears in the literature under several alternative abbreviations. It is handled as a research reagent rather than a pharmaceutical product.
A less common pathway for transmetalation is through a dissociative or solvent assisted mechanism. Here, a ligand from the tetravalent palladium species dissociates, and a coordinating solvent can add onto the palladium. When the solvent detaches, to form a 14-electron trivalent intermediate, the organostannane can add to the palladium, undergoing an open or cyclic type process as above.
=== Characters === Portal features two prominent characters: the player-controlled silent protagonist named Chell, and GLaDOS (Genetic Lifeform and Disk Operating System), a computer artificial intelligence that monitors and directs the player. In the English-language version, GLaDOS is voiced by Ellen McLain, though her voice has been altered to sound more artificial. The only background information presented about Chell is given by GLaDOS; the credibility of these facts, such as Chell being adopted, an orphan, and having no friends, is questionable at best, as GLaDOS is a liar by her own admission. In the "Lab Rat" comic created by Valve to bridge the gap between Portal and Portal 2, Chell's records reveal she was ultimately rejected as a test subject for having "too much tenacity"—the main reason Doug Rattmann, a former employee of Aperture Science, moved Chell to the top of the test queue.
=== La Canonja, Spain accident === On 14 January 2020 in an industrial estate near Tarragona, an explosion of an ethoxylation reactor owned by the chemical company Industrias Quimicas de Oxido de Etileno (IQOXE, part of the CL Industrial Group) occurred. The accident launched substantial debris over a radius of about two and a half kilometers, one piece penetrating a distant home and killing an occupant. It is reported that at least three people were killed and seven injured as a direct result of the explosion. The company was, until the time of the explosion the only producer of ethylene oxide in Spain with an installed capacity of 140,000 tons/year. Half of that production was used to manufacture ethylene glycol for PET production. The accident will be investigated under EU regulations within the context of the European Agency for Safety and Health at Work.
== Amino acid specificity == Many different amino acid side chains have been described as ADP-ribose acceptors. From a chemical perspective, this modification represents protein glycosylation: the transfer of ADP-ribose occurs onto amino acid side chains with a nucleophilic oxygen, nitrogen, or sulfur, resulting in N-, O-, or S-glycosidic linkage to the ribose of the ADP-ribose. Originally, acidic amino acids (glutamate and aspartate) were described as the main sites of ADP-ribosylation. However, many other ADP-ribose acceptor sites such as serine, arginine, cysteine, lysine, diphthamide, phosphoserine, and asparagine have been identified in subsequent works.
The other feature was a new cooling arrangement positioned aft (single ducted water and oil radiators assembly) that reduced the fuselage drag and effects on the wing. Later, after much development, they discovered that the cooling assembly could take advantage of the Meredith effect, in which heated air exited the radiator with a slight amount of jet thrust. Because NAA lacked a suitable wind tunnel to test this feature, it used the GALCIT 3.0 m (10 ft) wind tunnel at the California Institute of Technology. This led to some controversy over whether the Mustang's cooling system aerodynamics were developed by NAA's engineer Schmued or by Curtiss, as NAA had purchased the complete set of P-40 wind tunnel data and flight test reports. The NA-73X was also one of the first aircraft to have a fuselage lofted mathematically using conic sections; this resulted in smooth, low-drag surfaces. To aid production, the airframe was divided into five main sections—forward, center, rear fuselage, and two wing halves—all of which were fitted with wiring and piping before being joined. The prototype NA-73X was rolled out in September 1940, just 102 days after the order had been placed; it first flew on 26 October 1940, 149 days into the contract, an uncommonly short development period even during the war. With test pilot Vance Breese at the controls, the prototype handled well and accommodated an impressive fuel load. The aircraft's three-section, semi-monocoque fuselage was constructed entirely of 24S aluminum alloy (a type of Duralumin) to save weight.
Sources: en.wikipedia.org
=== Class II === Class II hydrophobins have overall a more conserved amino acid sequence between the different types and, contrary to class I, they have short, regular inter-cysteine spacing. Opposite to class I, the class II hydrophobins monolayer formed at hydrophobic:hydrophilic interfaces is not fibrillar and it is not associated with formation of amyloid-structures, nor with large conformational changes. Nonetheless, high resolution atomic-force microscopy studies revealed the formation of a notable hexagonal repeating pattern over surfaces coated with the class II hydrophobin HBFI, meaning that these proteins are also able to form an ordered network in surface films. The crystal structures or HFBI and HFBII from Trichoderma reesei were the first class II hydrophobins to be determined.
== Ethylene derivatives == These are generally mustard oils, which are characterized by a burning taste; their principal occurrence is in mustard and Tropaeolum seeds. Sinigrin, or the potassium salt of inyronic acid not only occurs in mustard seed, but also in black pepper and in horseradish root. Hydrolysis with barium hydroxide, or decomposition by the ferment myrosin, gives glucose, allyl mustard oil and potassium hydroxide. Sinalbin occurs in white pepper; it decomposes to the mustard oil, glucose and sinapin, a compound of choline and sinapic acid. Jalapin or Scammonin occurs in scammony; it hydrolyses to glucose and jalapinolic acid.
Odr-4 GPCR localization factor homolog, also known as C1orf27, is a protein in humans, encoded by the ODR4 gene. It is accession number NM_017847. This is a membrane protein that is 3926 base pairs long with the most extensive string of amino acids being 454aa long. C1orf27 exhibits cytoplasmic expression in epidermal tissues. Predicted associated biological processes of the gene include cell fate specification and developmental properties.
== Occurrence == Like other carotenoids, xanthophylls are found in highest quantity in the leaves of most green plants, where they act to modulate light energy and perhaps serve as a non-photochemical quenching agent to deal with triplet chlorophyll (an excited form of chlorophyll), which is overproduced at high light levels in photosynthesis. The xanthophylls found in the bodies of animals including humans, and in dietary animal products, are ultimately derived from plant sources in the diet. For example, the yellow color of chicken egg yolks, fat, and skin comes from ingested xanthophylls—primarily lutein, which is added to chicken feed for this purpose. The yellow color of the macula lutea (literally, yellow spot) in the retina of the human eye results from the presence of lutein and zeaxanthin. Again, both these specific xanthophylls require a source in the human diet to be present in the human eye. They absorb blue and ultraviolet light, thereby protecting the retina from the latter; but xanthophylls do not function in the mechanism of sight itself as they cannot be converted to retinal (also called retinaldehyde or vitamin A aldehyde). Their physical arrangement in the macula lutea is believed to be the cause of Haidinger's brush, an entoptic phenomenon that enables perception of polarized light.
Long-term exposure to air pollution may increase the risk of developing Parkinson's disease (PD). Components including particulate matter (PM2.5) and gases such as nitrogen dioxide (NO2), nitrogen oxides generally, ozone (O3) and carbon monoxide (CO) are associated with increased risk for PD. Higher PM2.5 levels correlate with increased PD hospitalization rates, for both short-term and long-term exposure. Air pollution is linked to Parkinson's disease through mechanisms of oxidative stress. PM2.5, NOx, and polycyclic aromatic hydrocarbons (PAHs) can cause the formation of reactive oxygen species (ROS). If there is an imbalance between the production of reactive oxygen species (ROS) and the body's ability to detoxify itself, this can lead to neuronal damage. Long-term exposure to air pollutants may lead to chronic oxidative stress and contribute to the progressive development of PD. Air pollution is also linked to increased risk of Parkinson's disease through mechanisms of systemic inflammation, neuroinflammation, and neuronal loss. Components of air pollution, particularly smaller particles, can reach the brain directly and contribute to PD pathology through direct neurotoxic effects or neuroinflammation. Exposure to air pollution can also cause peripheral inflammation of the lungs and other tissues, which can lead to systemic inflammation, weakening of the blood–brain barrier (BBB), and increased neuroinflammation.
Sources: en.wikipedia.org
TB-500 is a trade-style label for a synthetic peptide connected to thymosin beta-4. It is sold mainly through research-chemical channels and is not a single chemically defined product across suppliers.
Not necessarily. Some vendors use the name for the full 43-residue protein, while others apply it to a short actin-binding fragment or to a related tetrapeptide. The sequence should be confirmed from documentation rather than assumed from the label.
No thymosin beta-4 fragment holds marketing approval as a medicine in major jurisdictions. Material offered for sale is typically labelled for laboratory research only.
No. Thymosin beta-4 is a 43-residue natural peptide, while TB-500 is a commercial label applied to a short synthetic fragment of it. The two differ in length, sequence coverage and how they are handled in the laboratory.