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 2025-12-17 and is reviewed periodically as new material appears.
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.
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.
Thymosin beta-4 is a naturally occurring protein of 43 amino acids found in most mammalian cells, where it binds actin monomers and influences filament dynamics. It was first isolated from thymus tissue in the early 1980s, and its actin-binding activity was later mapped to a short region near the N-terminus. The synthetic fragment sold as TB-500 was designed to reproduce that region rather than the full protein. Whether a short fragment reproduces the behavior of the intact molecule remains an open question, since the parent protein carries additional structural elements outside the binding region.
| 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 |
Identity and purity are assessed with a small set of standard techniques. Reverse-phase high-performance liquid chromatography gives a purity estimate from peak area, usually recorded at 214 or 220 nanometers, where the peptide bond absorbs. Mass spectrometry confirms the expected molecular mass and can reveal truncated or oxidized species. Amino acid analysis or tandem mass spectrometry sequencing can verify the sequence itself. Additional quality attributes include water content, residual trifluoroacetic acid carried over from purification, and endotoxin where the material is intended for biological work.
The compound is most often distributed as a lyophilized powder, appearing white to off-white and forming a loose cake or fluffy solid. It is hygroscopic to some degree, so brief exposure to humid air can add water weight and complicate weighing. The peptide dissolves readily in water and in neutral aqueous buffers, and aqueous solubility is generally described as high, well above the concentrations used in typical assays. Some polar organic solvents are also usable, which matters when a concentrated stock is prepared before dilution into buffer.
Storage recommendations center on keeping the dry powder cold, dry, and dark. A freezer at -20 degrees Celsius or below is conventional, and desiccant is often included to limit moisture uptake. Once dissolved, the peptide is less stable, and solutions are typically kept frozen and thawed only once. Repeated freeze-thaw cycles are a common source of losses because they promote aggregation and adsorption to container surfaces. Working aliquots are therefore prepared in advance, and glass or low-binding plastic is usually preferred over ordinary laboratory plastic.
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.
Reconstitution of a lyophilized peptide is normally done with sterile water or a suitable buffer under aseptic conditions. Adding solvent down the vial wall and allowing gentle dissolution instead of vigorous vortexing reduces the chance of aggregation, which can lower the effective concentration of the resulting solution. Concentrated stocks are usually diluted into working buffer shortly before use. Because no standard preparation protocol exists for TB-500 specifically, laboratories adapt general peptide handling practice, and reported results may reflect differing preparation choices.
Dry peptide powder is commonly kept at −20 °C in a desiccated container away from light, a practice that limits moisture uptake and oxidation. Once dissolved, solutions are generally held at 2–8 °C for short periods or frozen at −20 °C or lower for longer storage, with repeated freeze-thaw cycles avoided. Hydrolysis and oxidation are the main degradation routes for peptides in solution, and both accelerate at higher temperature or extreme pH. Published stability data specific to TB-500 are limited, so shelf life should be treated as uncertain.
The International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) is a global professional association that promotes the fields of clinical chemistry and laboratory medicine. It was established in Paris in 1952 as the International Association of Clinical Biochemists to organize the various national societies of these fields and is based in Milan, Italy. The IFCC's aims are to set global standards, support and educate its members, and provide conferences and other gatherings for sharing knowledge among the global laboratory medicine community. IFCC members fall into three groups: national societies of clinical chemistry and laboratory medicine, corporations, and affiliate international or national societies involved in laboratory medicine. As of 2023, these members represented more than 45,000 individual clinical chemists, laboratory scientists, and laboratory physicians.
== In popular culture == Dover's powder was part of a joke published in The Science of Health in 1875 and reprinted in Godey's Lady's Book the same year. The joke illustrates its status as a typical medicine for a tumor:An old lady in Jefferson County acquired the habit of using morphia for relief from the pains of a tumor. Her family vainly dissuaded her, and at last united in deceiving her by substituting carefully prepared potato starch in morphia bottles. She used this article for fifteen years until the day of her death, often complaining that it was an inferior article, though her physician declared it all right. He gave her Dover's powders once during an illness, but she could not rest until she took some of the starch morphia.
=== Pharmacodynamics === Rivastigmine, a cholinesterase inhibitor, inhibits both butyrylcholinesterase and acetylcholinesterase (unlike donepezil, which selectively inhibits acetylcholinesterase). It is thought to work by inhibiting these cholinesterase enzymes, which would otherwise break down the brain neurotransmitter acetylcholine.
== Roles == Director, NIHR Leicester Biomedical Research Centre NIHR Senior Investigator Emeritus Co-chair, EASD/ADA Consensus Report on Type 2 Diabetes Management National Specialty Lead, Research Delivery Network for Diabetes, Metabolic and Endocrine
Sources: en.wikipedia.org
== Early life and legal career == Kerry-Lynne Findlay was born in 1955 in Ladysmith, British Columbia, and lived in Nanaimo and Victoria; her brother Greg Findlay was a linebacker for the BC Lions Canadian Football League (CFL) team. She comes from a family with many former CFL players; Findlay's father Stephen Findlay played for the Hamilton Tigers in the 23rd Grey Cup. After graduating from Crofton House School in Vancouver, she attended the University of British Columbia, receiving a Bachelor of Arts degree in history and political science in 1975, and a law degree in 1978. She articled at Kowarsky and Company in Vancouver, then worked there as an associate for two years before briefly serving as in-house counsel for the Insurance Corporation of British Columbia. She established her own practice in 1981, then joined Connell Lightbody in 1987 before switching to Watson Goepel Maledy in 1996. During her legal career, Findlay has been active in both the national and B.C. provincial branch of the Canadian Bar Association. She held various positions in that organization including national and provincial chair of the Constitutional Law Section and member of the National Task Force on Canadian Court Reform, and she was acclaimed president of the B.C. Branch for the 1997–1998 term. Findlay was appointed Queen's Counsel in March 1999 by the Attorney General of British Columbia, and served a five-year term as a Member of the Canadian Human Rights Tribunal by appointment of the Federal Minister of Justice (2006–2011).
With the exception of the Nautilidae and the species of octopus belonging to the suborder Cirrina, all known cephalopods have an ink sac, which can be used to expel a cloud of dark ink to confuse predators. This sac is a muscular bag which originated as an extension of the hindgut. It lies beneath the gut and opens into the anus, into which its contents – almost pure melanin – can be squirted; its proximity to the base of the funnel means the ink can be distributed by ejected water as the cephalopod uses its jet propulsion. The ejected cloud of melanin is usually mixed, upon expulsion, with mucus, produced elsewhere in the mantle, and therefore forms a thick cloud, resulting in visual (and possibly chemosensory) impairment of the predator, like a smokescreen. However, a more sophisticated behavior has been observed, in which the cephalopod releases a cloud, with a greater mucus content, that approximately resembles the cephalopod that released it (this decoy is referred to as a pseudomorph). This strategy often results in the predator attacking the pseudomorph, rather than its rapidly departing prey. For more information, see Inking behaviors. The ink sac of cephalopods has led to a common name of "inkfish", formerly the pen-and-ink fish.
== Education == The prevalence of stepfamilies has increased over the past century with the increase of divorce and remarriage. According to the Step Family Foundation, "over 50% of US families are remarried or recoupled." These families are unique in their experiences facing many challenges which first-married families do not. For example, role ambiguity, dealing with stepchildren, and ex-spouses are only a few of the issues which are unique to these families. In response to these families' desire for assistance, stepfamily education has become an increasingly common topic among scholars and educators. Although still a relatively new facet within the marriage education realm, stepfamily education provides important information which may not be addressed in traditional marriage or relationship education curriculum. As discussed by Adler-Baeder and Higginbotham (2004) a number of curricula are currently available to stepfamilies and family life educators; however, further research is needed in order to determine best practices for the field. One way in which this gap is being filled is through the current implementation of Healthy Marriage Demonstration Grants in the U.S. As part of the Deficit Reduction Act of 2005, grants for healthy marriage and responsible fatherhood, which include at-risk and diverse populations such as stepfamilies, are providing important information on the evaluation of stepfamily programs and their effectiveness in servicing stepfamilies.
== Localization == As a GPI-anchored protein, Thy-1 is present in the outer leaflet of lipid rafts in the cell membrane. In case of neurons it is known to be expressed strongly in the mature axon. The axon hillock can act as a barrier for its lateral spread even though it has no transmembrane segment. Thy-1 has been suggested to interact with G inhibitory proteins, the Src family kinase (SFK) member c-fyn, and tubulin within lipid rafts. In rats and mice, Thy-1 protein is present on the soma (cell body) and dendrites of neurons but is not expressed on axons until axonal growth is complete, and is again temporarily suppressed during axonal injury. HIV-1 Matrix co-localizes with Thy-1 in lipid rafts, the site of virus particle budding from cells, and Thy-1 is incorporated into virus particles as a result of this process.
=== Biostructural === The enzymatic chemistry involved in the formation of isopeptides for structural purposes is different from the case of ubiquitin and ubiquitin related proteins. In that, instead of sequential steps involving multiple enzymes to activate, conjugate and target the substrate. The catalysis is performed by one enzyme and the only precursor step, if there is one, is generally cleavage to activate it from a zymogen. However, the uniformity that exists in the ubiquitin's case is not so here, as there are numerous different enzymes all performing the reaction of forming the isopeptide bond. The first case is that of the sortases, an enzyme family that is spread throughout numerous gram positive bacteria. It has been shown to be an important pathogenicity and virulence factor. The general reaction performed by sortases involves using its own brand of the 'catalytic triad': i.e. using histidine, arginine, and cysteine for the reactive mechanism. His and Arg act to help create the reactive environment, and Cys once again acts as the reaction center by using a thioester help hold a carboxyl group until the amine of a Lysine can perform a nucleophilic attack to transfer the protein and form the isopeptide bond. An ion that can sometimes play an important although indirect role in the enzymatic reaction is calcium, which is bound by sortase. It plays an important role in holding the structure of the enzyme in the optimal conformation for catalysis. However, there are cases where calcium has been shown to be non-essential for catalysis to take place.
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.
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.