The short version of actin-binding motif fits in a sentence. The long version — which is the one that helps — is below.
This page was last updated on 2026-07-31 and is reviewed periodically as new material appears.
TB-500 is a laboratory label applied to a short synthetic peptide that is widely described as a fragment of thymosin beta-4, an actin-binding protein present in most mammalian cells. Suppliers and review articles usually present TB-500 as the N-terminal region of that protein, but the exact sequence attached to the name is not consistent across sources. Some product descriptions list a seven-residue chain; others use the label loosely for the parent protein itself. Because of that variation, any technical discussion of TB-500 needs to state which sequence is meant.
Thymosin beta-4 contains 43 amino acids and has a reported molecular mass near 4963 Da. The short fragment most often associated with the TB-500 label, an acetylated chain beginning LKKTETQ, has a reported mass near 889 Da, so the two are easily separated in analytical work. Mass spectrometry and amino acid analysis can confirm which material is present in a given sample. Statements treating TB-500 and thymosin beta-4 as interchangeable are therefore imprecise, even though the two appear together in much of the same literature.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Physical form | Lyophilised powder | Sealed vial; reconstituted before laboratory use |
| Appearance | White to off-white solid | Visual descriptor used on certificates of analysis |
| Solubility class | Water-soluble | Dissolves in water and aqueous buffers |
| Reported mass, fragment | Near 889 Da | Value depends on the stated sequence |
| Reported mass, parent protein | Near 4963 Da | 43-residue thymosin beta-4 |
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 peptide grew during the 2000s and 2010s, when studies of tendon and ligament injuries in horses reported changes in lesion size after treatment. Those reports circulated widely outside the scientific literature and shaped much of the current online discussion. Subsequent reviews noted inconsistent study design, small groups, and a shortage of independent replication. Popular descriptions often blur the line between the fragment, the complete protein, and unrelated growth factors, which complicates comparisons across sources.
TB-500 is a synthetic peptide whose sequence corresponds to a short fragment near the N-terminus of thymosin beta-4, a small protein present in most mammalian cells. The fragment is commonly cited as containing the actin-binding region of the parent molecule, which is why it appears in laboratory work on cell migration and tissue repair. Suppliers distribute it as a lyophilised powder intended for research use. Its identity is defined by amino acid sequence and by the presence of an acetyl group on the N-terminal residue.
Full-length thymosin beta-4 consists of roughly forty-three amino acids and ranks among the more abundant small proteins in the cytoplasm. The fragment is much shorter, so it cannot reproduce every function attributed to the intact molecule. In cell culture, short actin-binding motifs can interfere with filament dynamics and cell movement, but such observations come from controlled experiments rather than from whole-animal work. Whether a truncated fragment produces the same effects as the parent protein remains an open question.
Identity and purity are normally assessed with reversed-phase high-performance liquid chromatography, paired with mass spectrometry to confirm molecular mass. A certificate of analysis reports a purity percentage, usually derived from chromatographic peak area, but that figure does not by itself prove a correct sequence or the absence of counterions. Independent verification may include amino acid analysis or peptide mapping. Batch-to-batch variation is a documented concern in the research chemical market, and the gap between a quoted purity value and actual peptide content can be substantial when the material is a salt or retains residual water.
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.
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.
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.
== Biological roles == Highly dynamic disordered regions of proteins have been linked to functionally important phenomena such as allosteric regulation and enzyme catalysis. Many disordered proteins have the binding affinity with their receptors regulated by post-translational modification, thus it has been proposed that the flexibility of disordered proteins facilitates the different conformational requirements for binding the modifying enzymes as well as their receptors. Intrinsic disorder is particularly enriched in proteins implicated in cell signaling and transcription, as well as chromatin remodeling functions. Genes that have recently been born de novo tend to have higher disorder. In animals, genes with high disorder are lost at higher rates during evolution.
== Appendix: Download surveys / evaluations == The AIDA developers have undertaken a range of surveys and evaluations of usage of the AIDA diabetes simulator — to better understand who is downloading the program, and why. One initial study analysed data from 1,360 downloads of the AIDA software. The intended goals of the survey were: (i) to establish the feasibility of using the Internet for auditing and surveying diabetes software users; (ii) to identify the proportion of people with diabetes and their relatives who are actually making use of the program; and (iii) to establish certain technical details about downloaders' computer setups to facilitate the distribution of upgrades to the software. 1,360 responses were received over an 8-month period (from November 1999 to July 2000). During the corresponding period 3,821 actual downloads of the software were independently logged at the Website — giving a response rate to this survey of 35.6%. Responses were received from participants in 67 countries — although over half of these (n=730, 54%) originated from the US and UK. 762 responses (56%) were received from people with diabetes and 184 (13.5%) from relatives of patients, with lesser numbers from doctors, students, diabetes educators, nurses, pharmacists, and other end users. Useful technical information about computers and operating systems being used were also obtained. The initial study established the feasibility of using the Internet to survey, at no real cost, a large number of medical software downloaders / users.
When Aristotle says that the body is matter for a living thing, he may be using the word "body" to refer to the matter that makes up the fully organized body, rather than the fully organized body itself. Unlike the fully organized body, this "body" remains the same thing even after death. In contrast, when he says that the body is no longer the same after its death, he is using the word "body" to refer to the fully organized body.
Sources: en.wikipedia.org
=== Copolymer engineering === Copolymerization is used to modify the properties of manufactured plastics to meet specific needs, for example to reduce crystallinity, modify glass transition temperature, control wetting properties or to improve solubility. It is a way of improving mechanical properties, in a technique known as rubber toughening. Elastomeric phases within a rigid matrix act as crack arrestors, and so increase the energy absorption when the material is impacted for example. Acrylonitrile butadiene styrene is a common example.
=== Activism === Throughout her life, Kidder was active in environmental and anti-nuclear causes. On August 23, 2011, Kidder, Tantoo Cardinal, and dozens of others were arrested while protesting in Washington, DC, against the proposed extension of the Keystone Pipeline. In 2012, she appeared in a video for Stop the Frack Attack, an environmental organization working toward regulating hydraulic fracturing ("fracking") practices. When discussing sustainable energy, Kidder said: "The first thing people have to start facing, contrary to the advertising fed to us by oil and gas companies, is that environmentalism and economic stability go hand-in-hand on any long-term basis." Kidder spent the winter of 2016–2017 residing in a tent at the Standing Rock Reservation in North Dakota, protesting the Dakota Access Pipeline. In addition to environmental causes, Kidder was a vocal supporter of LGBTQ rights, and in 2003, hosted benefits at a gay and lesbian health center in Boston, Massachusetts. Following her publicized nervous breakdown in 1996, she also spoke outwardly about her struggles with mental health and her bipolar disorder diagnosis. In 2001, she was awarded the Courage in Mental Health Award from the California Women's Mental Health Policy Council for her public dialogue on mental illness.
=== Sources === Kosak, Dave (April 1, 2001). "Action Half-Life: Behind the Scenes". GameSpy. Retrieved 2017-07-04. Smith, Quintin (May 29, 2008). "3 – 2 – 1… Action Half-life". Rock, Paper, Shotgun. Retrieved 2017-07-04. Meer, Alec (June 8, 2009). "Action Half-Life 2: The Sauce Of Death". Rock, Paper, Shotgun. Retrieved 2017-07-04. Smith, Quintin (March 31, 2010). "Action Half-Life: The 5 a.m." Rock, Paper, Shotgun. Retrieved 2017-07-04. Smith, Quintin (May 23, 2011). "Stop, Drop, Roll: Action Half-Life 2 V2 Out". Rock, Paper, Shotgun. Retrieved 2017-07-04. Smith, Graham (May 8, 2014). "Total Converts: Unpotting The History Of Half-Life Modding". Rock, Paper, Shotgun. Retrieved 2017-07-04.
Antibiotic disks are used to test the ability for an antibiotic to inhibit growth of a microorganism. This method, which is commonly used with Mueller–Hinton agar, is used by evenly seeding bacteria over a petri dish and applying an antibiotic treated disk to the top of the agar. By observing the ring formed around the disk formed due to the lack of bacterial growth, the zone of inhibition can be found, which is used to find the susceptibility of an organism to an antibiotic.
Sources: en.wikipedia.org
No. TB-500 is a trade-style label used for a synthetic peptide described as a fragment of thymosin beta-4, while thymosin beta-4 is the full 43-residue protein. The two differ in size and are not interchangeable terms in analytical work.
Naming for research peptides is not standardised, and suppliers sometimes apply the same label to different chain lengths. Certificates of analysis and mass data are the practical way to determine what a given lot contains.
The fragment commonly cited under this label is reported near 889 Da, and the parent protein near 4963 Da. Reported values shift with the exact sequence and with residual counter-ions or water in the sample.
The lyophilised powder is typically held at -20 C or lower in a dry, dark place. Reconstituted solutions are aliquoted and frozen to avoid repeated freeze-thaw cycles.