The short version of Ac-LKKTETQ fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2025-08-18. Anything still debated is marked as such rather than presented as settled.
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.
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.
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.
| 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 |
Once in solution, short peptides are generally less stable than the dry powder, and repeated freeze-thaw cycles are a common cause of loss. Laboratory guidance usually calls for aliquoting on first dissolution and storing aliquots at -20 °C or below, away from light. Adsorption to plastic and glass surfaces can lower measured concentration, particularly at low concentrations, so container material and buffer choice can affect results. Visible cloudiness, colour change or unexpected precipitate is a signal to re-check the material.
Purity is normally assessed by reversed-phase HPLC, with the main peak reported as a percentage of total peak area, while identity is confirmed by mass spectrometry. Electrospray and MALDI-TOF instruments are both used, and the observed mass is compared with the value calculated from the stated sequence. Ion-exchange or size-exclusion methods appear where aggregation or charge variants are of interest. Water content, counter-ion content and residual trifluoroacetate from purification are separate variables that can shift the measured mass and should be weighed when reading a certificate of analysis.
Lyophilized peptide arrives as a dry cake that should stay sealed until use. Reconstitution is generally performed with sterile water or a buffered solution, and the resulting liquid should be handled gently to limit mechanical stress. Repeated freeze-thaw cycles are widely described as harmful to short peptides, so dividing a reconstituted batch into single-use portions is a common practice. Laboratories also record the solvent, concentration, and date of preparation on the vial label to keep later measurements traceable.
Dry powder is commonly held at minus twenty degrees Celsius, with some suppliers recommending lower temperatures for long-term archival storage. Once dissolved, solutions are typically kept cold and protected from light, since aqueous peptide solutions can lose integrity through hydrolysis or oxidation over time. Stability data specific to this fragment are limited in the public literature, and much of the guidance comes from general peptide handling practice rather than from controlled degradation studies. Users therefore treat stated shelf lives as approximate rather than fixed.
Opioid withdrawal can occur with a sudden decrease in, or cessation of, opioids after prolonged use. Onset of withdrawal depends on the half-life of the opioid that was used last. With heroin this typically occurs five hours after use. With methadone, it may take two days. How long major symptoms last also depends on the opioid used. For heroin withdrawal, symptoms are typically greatest at two to four days and can last up to two weeks. Less significant symptoms may last longer, in which case the withdrawal is known as post-acute-withdrawal syndrome.
Varicella vaccine, also known as chickenpox vaccine, is a vaccine that protects against chickenpox. One dose of vaccine prevents 95% of moderate disease and 100% of severe disease. Two doses of vaccine are more effective than one. If given to those who are not immune within five days of exposure to chickenpox it prevents most cases of the disease. Vaccinating a large portion of the population also protects those who are not vaccinated. It is given by injection just under the skin. Another vaccine, known as zoster vaccine, is used to prevent diseases caused by the same virus – the varicella zoster virus. The World Health Organization (WHO) recommends routine vaccination only if a country can keep more than 80% of people vaccinated. If only 20% to 80% of people are vaccinated it is possible that more people will get the disease at an older age and outcomes overall may worsen. Either one or two doses of the vaccine are recommended. In the United States two doses are recommended starting at twelve to fifteen months of age. As of 2017, twenty-three countries recommend all non-medically exempt children receive the vaccine, nine recommend it only for high-risk groups, three additional countries recommend use in only parts of the country, while other countries make no recommendation. Not all countries provide the vaccine due to its cost. In the United Kingdom, the varicella vaccine has been added in 2026 to the routine children vaccination, combined with the MMR vaccine, at ages 12 and 18 months. Minor side effects may include pain at the site of injection, fever, and rash.
α-Methylphenylalanine (α-MePhe or AMPA) is an artificial amino acid and a phenethylamine and amphetamine derivative. It is the α-methylated analogue of phenylalanine, the precursor of the catecholamine neurotransmitters, and the amino acid analogue of amphetamine (α-methylphenethylamine), a psychostimulant and monoamine releasing agent. α-MePhe is a tyrosine hydroxylase inhibitor, thereby preventing the transformation of tyrosine into L-DOPA, and results in depletion of the catecholamine neurotransmitters. It is also an inhibitor of phenylalanine hydroxylase, and in conjunction with phenylalanine administration, induces hyperphenylalaninemia analogous to that in phenylketonuria in animals. The drug is known to produce metaraminol (3,β-dihydroxyamphetamine), a catecholamine releasing agent, as an active metabolite in animals, and this metabolite contributes to its effects. α-MePhe is a substrate of the L-type amino acid transporter 1 (LAT1), which transports it across the blood–brain barrier into the central nervous system.
The crew landed on the reciprocal runway with no further incident. No casualties. On September 21, 2001, RA-86074 (c/n 041) operating as Aeroflot Flight 521 belly-landed at Dubai after a flight from Moscow, the flight crew having switched off the ground proximity warning due to heavy workload on the approach and then neglected to extend the landing gear; no casualties; aircraft written off. On July 28, 2002, Pulkovo Aviation Enterprise Flight 9560 RA-86060 (c/n 027) crashed shortly after departure from Moscow on a repositioning flight to Saint Peterburg. The trim toggle button on the control column caused a spontaneous retrimming of the tailplane, rapid transition to nose-heavy trim and a dive. The four flightdeck crew, two ground support staff and ten cabin crew aboard the aircraft died, making the crash the deadliest aviation accident involving the Il-86. The two injured survivors were cabin crew members. Following the Moscow crash in July 2002, the MAK Interstate Aviation Committee withdrew the Il-86's certificate of airworthiness, temporarily grounding the type. The certificate was rapidly restored in stages by early 2003. The accident prompted the Egyptian civil aviation authorities to attempt to ban Il-86 operations to Egypt. Amid continuing negotiations, by 2007 the intention had lapsed, with intensive Il-86 operations to and from Egypt continuing.
== Structure == The human OGT gene has 1046 amino acid residues, and is a heterotrimer consisting of two 110 kDa subunits and one 78 kDa subunit. The 110 kDa subunit contains 13 tetratricopeptide repeats (TPRs); the 13th repeat is truncated. These subunits are dimerized by TPR repeats 6 and 7. OGT is highly expressed in the pancreas and also expressed in the heart, brain, skeletal muscle, and the placenta. There have been trace amounts found in the lung and the liver. The binding sites have been determined for the 110 kDa subunit. It has 3 binding sites at amino acid residues 849, 852, and 935. The probable active site is at residue 508. The crystal structure of O-GlcNAc transferase has not been well studied, but the structure of a binary complex with UDP and a ternary complex with UDP and a peptide substrate has been researched. The OGT-UDP complex contains three domains in its catalytic region: the amino (N)-terminal domain, the carboxy (C)-terminal domain, and the intervening domain (Int-D). The catalytic region is linked to TPR repeats by a translational helix (H3), which loops from the C-cat domain to the N-cat domain along the upper surface of the catalytic region. The OGT-UDP-peptide complex has a larger space between the TPR domain and the catalytic region than the OGT-UDP complex. The CKII peptide, which contains three serine residues and a threonine residue, binds in this space.
Sources: en.wikipedia.org
Fluorinated surfactants or fluorosurfactants are a subgroup of PFAS characterized by a hydrophobic fluorinated "tail" and a hydrophilic "head" that behave as surfactants. These are more effective at reducing the surface tension of water than comparable hydrocarbon surfactants. Fluorosurfactants tend to concentrate at the phase interfaces. Fluorocarbons are both lipophobic and hydrophobic, repelling both oil and water. Their lipophobicity results from the relative lack of London dispersion forces compared to hydrocarbons, a consequence of fluorine's large electronegativity and small bond length, which reduce the polarizability of the surfactants' fluorinated molecular surface. Fluorosurfactants are more stable than hydrocarbon surfactants due to the stability of the carbon–fluorine bond. Perfluorinated surfactants persist in the environment for the same reason. Fluorosurfactants such as PFOS, PFOA, and perfluorononanoic acid (PFNA) have caught the attention of regulatory agencies because of their persistence, toxicity, and widespread occurrence in the blood of general populations.
=== Quaternary structure === Chymopapain presents a quaternary structure characterized by the formation of homo dimers, which means that two chymopapain chains join each other through weak interactions to conform one unique biological structure.
A psychometric function with a log concentration–perceived intensity plot is characterised by its sigmoidal shape, with its initial baseline representing the compound at concentrations below its threshold, a slow rise in response around the inflection point representing the threshold, an exponential rise in response as the concentration exceeds the threshold, a deceleration of the response to a flat region as the zone of saturation or the point at which the change in intensity is no longer perceived is reached. On the other hand, a log concentration–log perceived intensity plot, using Steven's power law, forms a linear line with the exponent characterising the relationship between the two variables.
==== In cattle ==== Canadian researchers used yearling heifers to determine the relative pain of the two branding methods. Thirty animals were randomly assigned either a hot, freeze or sham branding. Blood samples were drawn every 20 minutes, beginning 20 minutes before branding and for 3 hours after. Each heifer in the hot group was branded with three separate steel irons for a total of 9–15 seconds (3–5 seconds per iron), while heifers in the freeze group were branded with three separate copper irons (of the same design as the hot group) for a total of 60 seconds (20 seconds per iron). Cattle in the sham group were placed in the same squeeze chute used for the real brandings. The animals were shaved in this restraint and then held there for 3 minutes, the mean duration of the actual brandings. The results showed that both hot and freeze-branded cattle had elevated cortisol levels compared with the sham-branded group. Hot and freeze-branded animals had similar maximum elevations, which occurred 20 minutes after branding. Cortisol levels in the hot-branded group took longer to return to baseline than either the freeze or sham-branded heifers. No significant difference in cortisol concentration was noted between the two branded groups after 40 minutes post-branding. No significant differences between the three groups were detected with the other proxies the experimenters selected for pain (touch sensitivity and stress-induced analgesia). The authors concluded that,
Sources: en.wikipedia.org
=== Development of pretargeted imaging === To bypass the problem associated with the prolonged circulation time of radiolabelled antibodies, in the mid-1980s a strategy called pretargeted radioimmunotherapy was developed. In short, this approach contained two important steps: 1. administration of a macromolecular targeting vector (usually antibody-based), and 2. a small radiolabelled molecule, which interacts with the targeting vector. Most importantly the small radiolabelled molecule gets injected after a predetermined lag period after which the macromolecule has had enough time to bind to its target and the residual unbound macromolecule to be cleared out of the system. To ensure sufficient interaction between the two components, suitable modifications with complementary species are required (like bioorthogonal modifications). Pretargeting strategies can lead to an improved imaging contrast, as it combines the high target specificity and affinity of an antibody with the fast pharmacokinetic properties of a small molecule. The concept of pretargeting, although existing for several decades already, was limited to a few distinct classes. Developing chemical reactions that proceed quickly within living systems, without interacting with the large variety of existing functional groups, used to be an inherent difficulty. However, there have been several advancements in this area over the past few years.
=== Side effects === Side effects in animals include transient hypertension and hypotension. Xylazine decreases both respiration rate and minute ventilation, although the changes to PaCO2 and PaO2 are minor and innocuous. Xylazine has been demonstrated to reduce the dose of epinephrine that causes arrythmia in dogs anaesthetised with isoflurane and halothane. Xylazine administration in sheep activates pulmonary macrophages that damage the capillary endothelium and alveolar type I cells. This in turns causes alveolar haemorrhage and oedema causing hypoxaemia. Intracarotid administration can cause seizures and excitement in horses. Xylazine has been shown to cause myometrial contractions in pregnant cattle. Further evidence of xylazine's effect on pregnant animals is lacking and although other a2 adrenergic receptor agonists have been shown to not cause the same myometrial contraction the administration of a2 adrenergic receptor agonists is not recommended and for animals near-term should only be used in specific circumstances. Xylazine affects the glucose level via the activation of alpha2A andrenergic receptors on beta cells, which prevents insulin release. alpha2 adrenergic receptors have been reported to cause transient hyperglycaemia with xylazine being reported as a cause in cattle and equine. The renal threshold for glucose is not exceeded due to the hyperglycaemia with clinical doses. An alpha2 adrenergic receptor antagonist can reverse the effect.
== Cancer == Recently, SCF complexes have become an attractive anti-cancer target because of their upregulation in some human cancers and their biochemically distinct active sites. Though many of the aforementioned FBPs have been implicated in cancer, cytotoxicity has been a limiting factor of drug development. Skp2-targeting anti-sense oligonucleotides and siRNAs are in the drug development pipeline. Preliminary studies have shown that Skp2 downregulation can inhibit the growth of melanomas, lung cancer cells, oral cancer cells, and glioblastoma cells. βTRCP-targeting siRNAs have been shown to sensitize breast cancer cells and cervical cancer cells to existing chemotherapies.
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.
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.