If you have been reading about TB-500 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 2026-04-30. Numbers and descriptions here follow the published literature rather than marketing material.
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.
TB-500 is a shorthand label used in supplier catalogs and online discussion for a short synthetic peptide described as a fragment of thymosin beta-4. Most product listings present it as the N-terminally acetylated heptapeptide Ac-LKKTETQ, a sequence corresponding to the actin-binding region of the parent protein. The name is not a formal chemical designation and does not appear in standard nomenclature systems. Because labeling practices vary between vendors, two products sold under the same name may not contain the same molecule, and the stated sequence should be treated as a claim rather than a fixed definition.
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.
Proposed activity centers on actin sequestration and on the movement of cells during repair processes. In cell culture and animal models, the fragment has been associated with migration, tube formation, and tissue remodeling. These observations are frequently described as preliminary, because most published work uses rodent or in vitro systems rather than controlled human trials. Whether the short fragment reproduces the effects of the full protein remains an open question, and the relationship between dose, route, and measured outcome is not well characterized.
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.
| Property | Value | Notes |
|---|---|---|
| Reported sequence | Ac-LKKTETQ | Described in most listings as the actin-binding region of thymosin beta-4 |
| Reported molecular weight | Approximately 889 Da | Value shifts with the stated sequence; compare against the certificate of analysis |
| Parent protein length | 43 amino acids | Thymosin beta-4; the fragment covers only a small part of it |
| Common synonyms | TB4 fragment; thymosin beta-4 fragment | Trade-style names rather than formal nomenclature |
| Formal monographs | Not established | Labeling conventions differ by supplier and region |
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.
Identity and purity are usually assessed by reversed-phase high-performance liquid chromatography together with mass spectrometry. The chromatogram provides a purity estimate as a percentage of total peak area, while the mass spectrum confirms that the observed mass matches the expected value. Amino acid analysis or tandem mass spectrometry sequencing can provide additional confirmation. Reported purity figures depend on the column, gradient, and detection wavelength, so values from different laboratories are not directly comparable without method details.
Lyophilised peptide is normally reconstituted with sterile water or a neutral buffer shortly before use. Because repeated freeze-thaw cycles can degrade the material, dividing a reconstituted solution into single-use aliquots is a common practice. Working solutions are usually kept cold and protected from light. The exact shelf life depends on concentration, buffer composition, and handling, so it is often determined empirically rather than assumed.
Peptide bonds are susceptible to hydrolysis under extreme pH and to enzymatic cleavage if proteases are present. Heat, oxidising agents, and prolonged exposure to light also contribute to loss of material. Aggregation can occur at high concentrations or in certain buffer systems, and it may not be visible to the eye. Storage at -20 C or below is typical for both powder and aliquoted solutions, and desiccation of the powder is preferred.
Hydroxylysine (Hyl) is an amino acid with the molecular formula C6H14N2O3. It was first discovered in 1921 by Donald Van Slyke as the 5-hydroxylysine form. It arises from a post-translational hydroxy modification of lysine. It is most widely known as a component of collagen. It is biosynthesized from lysine via oxidation by lysyl hydroxylase enzymes. The most common form is the (5R) stereoisomer found in collagen. However, the enzyme JMJD6 has recently been shown to be a lysyl hydroxylase which modifies an RNA splicing factor producing the (5S) stereoisomer. Additionally, in E. coli, there has been at least one lysine N-hydroxylase enzyme identified, named IucD.
== History == The group began as a jangly indie pop band influenced by Primal Scream's early sound. By the time they recorded their first EP, Barging Into the Presence of God, released in 1989, the band went into a direction that displayed a mix of Ian Masters' ethereal, choirboy-like vocals along with dark atmospheric and noisy pop tunes. Ashley Horner from Edsel Auctioneer briefly joined the band on guitar in the same year. The band was signed to 4AD Records after their first London show by the label's chief Ivo Watts-Russell. The group's first album, The Comforts of Madness, was released in 1990 and reached the top 40 of the UK Albums Chart. The album's tracks were produced by John Fryer and Gil Norton. The album includes a cover version of "Fell from the Sun" by Opal. In late 1990, Meriel Barham, the original vocalist of Lush, joined the band as second guitarist and vocalist. Barham contributed backing vocals and guitars to the Chris Allison produced Half-Life EP, then joined permanently for the Nancy Sinatra cover "Kinky Love", which gave the band a minor hit single as part of Flesh Balloon EP. In 1992 the band recorded their second full-length album, In Ribbons, which was produced by Hugh Jones. Ian Masters left the band in 1993, citing his lack of enthusiasm for touring, unlike the remaining members of the band and their record label 4AD. Former Heart Throbs bassist Colleen Browne joined afterwards. Sticking with producer Hugh Jones, the group released the Fine Friend EP in mid-1994, followed by their third album, Slow Buildings.
=== Wild animals === Wildlife species, primarily bats, raccoons, skunks, and foxes, act as reservoir species for different variants of the rabies virus in distinct geographic regions of the United States. This results in the general occurrence of rabies as well as outbreaks in animal populations. Approximately 90% of all reported rabies cases in the US are from wildlife. Injections are too laborious for reaching enough animals to reach herd immunity, so oral rabies vaccines (ORVs) are used instead. ORVs are incorporated into food baits and scattered across the landscape for them to be eaten. When an animal bites into the bait, the packets burst and the vaccine is administered. Current research suggests that if adequate amounts of the vaccine is ingested, immunity to the virus should last for upwards of one year. By immunizing wild or stray animals, ORV programs work to create a buffer zone between the rabies virus and potential contact with humans, pets, or livestock. Landscape features such as large bodies of water and mountains are often used to enhance the effectiveness of the buffer. The effectiveness of ORV campaigns in specific areas is determined through trap-and-release methods. Titer tests are performed on the blood drawn from the sample animals in order to measure rabies antibody levels in the blood. Baits are usually distributed by aircraft to more efficiently cover large, rural regions. In order to place baits more precisely and to minimize human and pet contact with baits, they are distributed by hand in suburban or urban regions.
Sources: en.wikipedia.org
=== In popular culture === U-47700 is the title of a 2021 Dutch sci-fi short film by director Erasmo de la Parra. In the film, the characters are addicted to a new drug containing the substance U-47700.
=== Enterohepatic circulation === Research by Aarons has focused on enterohepatic cycling (EHC) which refers to the process whereby a drug goes through the liver and biliary tract for excretion and is released into the small intestine, where it can be reabsorbed back into circulation and subsequently returned to the liver. This can cause liver damage and the half-life and duration of a drug to be increased. Aarons and his team stressed that knowing the extent of EHC is invaluable in deciding whether or not the in vitro characteristics of a drug - i.e. those taking place outside of a living organism - will have any effect on the overall process of absorption in vivo, or when it is taking place inside the organism. Aarons had earlier been involved in research on the area under the curve (AUC). This is a pharmacokinetic statistic used to describe the total exposure to a drug - specifically the concentration of a drug in body fluids such as blood - and is useful because it gives insight into the extent of exposure to a drug and its clearance rate from the body. The research was seen as important in the "design of sampling protocols for accurate determination of AUC(0– ∞) for drugs subject to enterohepatic cycling."
== Cause == The most common underlying pathology leading to TIA and stroke is a cardiac condition called atrial fibrillation, where poor coordination of heart contraction may lead to the formation of a clot in the atrial chamber that can become dislodged and travel to a cerebral artery. Unlike in stroke, the blood flow can become restored prior to infarction which leads to the resolution of neurologic symptoms. Another common culprit of TIA is an atherosclerotic plaque located in the common carotid artery, typically by the bifurcation between the internal and external carotids, that becomes an embolism to the brain vasculature similar to the clot in the prior example. A portion of the plaque can become dislodged and lead to embolic pathology in the cerebral vessels. In-situ thrombosis, an obstruction that forms directly in the cerebral vasculature unlike the remote embolism previously mentioned, is another vascular occurrence with possible presentation as TIA. Also, carotid stenosis secondary to atherosclerosis narrowing the diameter of the lumen and thus limiting blood flow is another common cause of TIA. Individuals with carotid stenosis may present with TIA symptoms, thus labeled symptomatic, while others may not experience symptoms and be asymptomatic.
Gas amplifier pumps were ideal because they operated at constant pressure and did not require leak-free seals or check valves for steady flow and good quantitation. Hardware milestones were made at Dupont IPD (Industrial Polymers Division) such as a low-dwell-volume gradient device being utilized as well as replacing the septum injector with a loop injection valve. While instrumentation developments were important, the history of HPLC is primarily about the history and evolution of particle technology. After the introduction of porous layer particles, there has been a steady trend to reduced particle size to improve efficiency. However, by decreasing particle size, new problems arose. The practical disadvantages stem from the excessive pressure drop needed to force mobile fluid through the column and the difficulty of preparing a uniform packing of extremely fine materials. Every time particle size is reduced significantly, another round of instrument development usually must occur to handle the pressure.
Sources: en.wikipedia.org
=== Qualitative analysis === Generally, chromatographic data is presented as a graph of detector response (y-axis) against retention time (x-axis), which is called a chromatogram. This provides a spectrum of peaks for a sample representing the analytes present in a sample eluting from the column at different times. Retention time can be used to identify analytes if the method conditions are constant. Also, the pattern of peaks will be constant for a sample under constant conditions and can identify complex mixtures of analytes. However, in most modern applications, the GC is connected to a mass spectrometer or similar detector that is capable of identifying the analytes represented by the peaks.
These genes can be placed in three categories: genes that increase the risk of migraine in general, those that specifically increase risk for migraine with aura, and those that specifically increase risk for migraine without aura. Three of these genes, CALCA, CALCB, and HTR1F, are already targets for migraine specific treatments. Five genes are specific to risk of migraine with aura, PALMD, ABO, LRRK2, CACNA1A and PRRT2, and 13 genes are specific to risk of migraine without aura. Using the accumulated genetic risk of common variations to calculate a so-called polygenetic risk score, it is possible to assess, for example, the treatment response to triptans.
Amine groups are found throughout an antibody and are used as a target due to their easy steric accessibility and modification. An overview of this reaction is found in Figure 2. Most often amine groups found on lysine are covalently bonded to carboxyl groups of glutamic and aspartic acid on formed liposomes using certain agents. A two step process is utilized where the first step uses 1-ethyl-3-[3-dimethylaminopropyl] carbodiimide to create an amine reactive product from the carboxyl group. This product is a target for a nucleophilic attack by the amine but it hydrolyzes quickly, so EDC is added to stabilize it. As seen in the Figure 2, the intermediate can lead to the desired stable amide bond by chance or the recreation of a carboxyl group. To create more of the desired carboxyl-amine bond, N-hydroxysulfosuccinimide (sulfo-NHS) is added to form another intermediate that is an NHS ester. The second step to this reaction is for the antibodies to use the N-terminus of the lipid to covalently conjugate by creating an amide bond via displacement of sulfo-NHS groups. This leads to the final product of an antibody conjugated to a liposome to create an immunoliposome. This process is highly efficient and effective while maintaining the biological activity of the antibody.
=== Other uses === 4-Nitrophenol is an intermediate in the synthesis of paracetamol. It is reduced to 4-aminophenol, then acetylated with acetic anhydride. 4-Nitrophenol is used as the precursor for the preparation of phenetidine and acetophenetidine, indicators, and raw materials for fungicides. Bioaccumulation of this compound rarely occurs. In peptide synthesis, carboxylate ester derivatives of 4-nitrophenol may serve as activated components for construction of amide moieties. In drug chemistry (medicine), 4-nitrophenol finds utility in the synthesis of fedratinib & glutaurine (protecting group).
These effects were not noted in its medicinal use in the 1950s and 1960s, and reports of physical violence on PCP have often been shown to be unfounded. Recreational doses of the drug also occasionally appear to induce a psychotic state, with emotional and cognitive impairment that resembles a schizophrenic episode. Users generally report feeling detached from reality. Symptoms are summarized by the mnemonic device RED DANES: rage, erythema (redness of skin), dilated pupils, delusions, amnesia, nystagmus (oscillation of the eyeball when moving laterally), excitation, and skin dryness.
Sources: en.wikipedia.org
Most listings describe it as a short acetylated peptide with the sequence Ac-LKKTETQ, presented as a region of thymosin beta-4. The label is a trade-style name rather than a standardized chemical name, so the exact content of a given vial depends on the supplier.
No. Thymosin beta-4 is a protein of 43 amino acids, while TB-500 is described as a short fragment of it. The two differ in size, structure, and the range of interactions each can support.
Naming for research peptides is not centrally coordinated, so vendors set their own labels and specifications. Differences in stated sequence, molecular weight, or purity documentation usually trace back to those independent labeling choices.
TB-500 is a name used for a short synthetic peptide fragment taken from the actin-binding region of thymosin beta-4. Material sold under this label is usually a lyophilized powder supplied for laboratory research rather than a licensed medicine. The commonly cited sequence is LKKTETQ.