The short version of actin binding fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2026-04-19. Anything still debated is marked as such rather than presented as settled.
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.
Detection in biological samples relies on mass spectrometry, typically liquid chromatography coupled to tandem mass spectrometry after peptide extraction and enrichment. Intact peptides can also be confirmed by high-resolution mass measurement together with fragmentation data. Detection windows in urine are short because the peptide is degraded by proteases and cleared quickly, and concentrations are low. Many jurisdictions treat the compound as a prohibited substance in sport, grouped with peptide hormones and related factors, while it is not an approved therapeutic product. Identity and purity statements therefore rest on certificates of analysis, ideally issued by an independent laboratory.
Material is normally supplied as a lyophilised powder in a sealed vial. The powder is hygroscopic, so exposure to humid air leads to water uptake, caking and gradual loss of the fluffy texture that indicates a good freeze-dry. Vials are best kept sealed with desiccant, protected from light and stored cold. Letting a cold vial warm to room temperature before opening reduces condensation on the contents. Purity is normally reported from a chromatographic run, and that figure applies to the batch as tested rather than to the vial after repeated opening.
| Property | Value | Notes |
|---|---|---|
| Name type | Commercial trade name | Not a systematic chemical identifier |
| Parent peptide | Thymosin beta-4 | 43-residue natural peptide |
| Common fragment sequence | LKKTETQ | Maps to part of the actin-binding region |
| Molecular size class | Roughly 0.8-1.0 kDa | Depends on exact fragment and terminal modification |
| Regulatory status | Prohibited in sport | Grouped with peptide hormones in many frameworks |
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 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.
Lyophilized TB-500 is hygroscopic and should be kept dry before use. The usual storage recommendation for the solid is -20 °C, protected from light and moisture. Once dissolved, the peptide is less stable, and repeated freeze-thaw cycles can promote aggregation or degradation. Laboratories often divide a reconstituted solution into single-use aliquots and store them at -80 °C. Exact stability limits depend on buffer, pH, and concentration, so published data do not define a single universal condition.
Identity and purity are checked with chromatographic and mass spectrometric methods. Reverse-phase high-performance liquid chromatography separates the peptide from related impurities, while mass spectrometry confirms the expected molecular mass. A certificate of analysis may report a purity percentage, but the laboratory should still verify the material independently. Common quality concerns include truncated sequences, deamidation, oxidation, and residual solvents from synthesis. Because TB-500 is short, some impurities can differ from the target by only a few mass units.
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.
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.
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.
=== Dipole moment === The dipole moment has an important role in orienting proteins to the proper directions and enhancing their abilities to bind to other molecules. The dipole moment of cytochrome c results from a cluster of negatively charged amino acid side chains at the "back" of the enzyme. Despite variations in the number of bound heme groups and variations in sequence, the dipole moment of vertebrate cytochromes c is remarkably conserved. For example, vertebrate cytochromes c all have a dipole moment of approximately 320 debye while cytochromes c of plants and insects have a dipole moment of approximately 340 debye.
=== Digital === The library's first digitization project, American Memory, was launched in 1990, and was initially planned to choose 160 million objects from its collection to make digitally available on LaserDiscs and CDs, which were distributed to schools and libraries. After realizing that this plan would be too expensive and inefficient, and with the rise of the Internet, the library decided to instead make digitized material available over the Internet. This project was made official in the National Digital Library Program (NDLP), created in October 1994. By 1999, the NDLP had succeeded in digitizing over 5 million objects and had a budget of $12 million. As of 2022, the library's website contains 914 million unique digital objects, comprising over 21 petabytes of data. American Memory is a source for public domain image resources, as well as audio, video, and archived Web content. Nearly all of the lists of holdings, the catalogs of the library, can be consulted directly on its website. Librarians all over the world consult these catalogs, through the Web or through other media better suited to their needs, when they need to catalog for their collection a book published in the United States. They use the Library of Congress Control Number to make sure of the exact identity of the book. Digital images are also available at Snapshots of the Past, which provides archival prints. The library has a budget of $6–8 million each year for digitization, meaning that not all works can be digitized.
Sweat is mostly water. A microfluidic model of the eccrine sweat gland provides details on what solutes partition into sweat, their mechanisms of partitioning, and their fluidic transport to the skin surface. Dissolved in the water are trace amounts of minerals, lactic acid, and urea. Although the mineral content varies, some measured concentrations are: sodium (0.9 gram/litre), potassium (0.2 g/L), calcium (0.015 g/L), and magnesium (0.0013 g/L). Relative to the plasma and extracellular fluid, the concentration of Na+ ions is much lower in sweat (≈40 mM in sweat versus ≈150 mM in plasma and extracellular fluid). Initially, within eccrine glands sweat has a high concentration of Na+ ions. In the sweat ducts, the Na+ ions are re-absorbed into tissue by epithelial sodium channels (ENaC) that are located on the apical membrane of epithelial cells that form the duct (see Fig. 9 of the reference). Many other trace elements are also excreted in sweat, again an indication of their concentration is (although measurements can vary fifteenfold) zinc (0.4 milligrams/litre), copper (0.3–0.8 mg/L), iron (1 mg/L), chromium (0.1 mg/L), nickel (0.05 mg/L), and lead (0.05 mg/L). Probably many other less-abundant trace minerals leave the body through sweating with correspondingly lower concentrations. Some exogenous organic compounds make their way into sweat as exemplified by an unidentified odiferous "maple syrup" scented compound in several of the species in the mushroom genus Lactarius. In humans, sweat is hypoosmotic relative to plasma (i.e. less concentrated).
== Overview == A sample large-scale phosphoproteomic analysis includes cultured cells undergo SILAC encoding; cells are stimulated with factor of interest (e.g. growth factor, hormone); stimulation can occur for various lengths of time for temporal analysis, cells are lysed and enzymatically digested, peptides are separated using ion exchange chromatography; phosphopeptides are enriched using phosphospecific antibodies, immobilized metal affinity chromatography or titanium dioxide (TiO2) chromatography; phosphopeptides are analyzed using mass spectrometry, and peptides are sequenced and analyzed.
== Evolutionary implications == Most humans have multiple copies of the regulatory gene sequence for prodynorphin, which is virtually identical among all primates, whereas other primates have only a single copy. In addition, most Asian populations have two copies of the gene sequence for prodynorphin, whereas East Africas, Middle Easterners, and Europeans tend to have three repetitions. The extent of regulatory gene disparities for prodynorphin, between human and primates, has gained the attention of scientists. There are very few genes known to be directly related to mankind's speciation from other great apes. According to computational biologist researcher Matthew W. Hahn of Indiana University, "this is the first documented instance of a neural gene that has had its regulation shaped by natural selection during human origins." The prodynorphin polypeptide is identical in humans and chimpanzees, but the regulatory promoter sequences have been shown to exhibit marked differences. According to Hahn, "humans have the ability to turn on this gene more easily and more intensely than other primates", a reason why regulation of this gene may have been important in the evolution of modern humans' mental capacity.
Sources: en.wikipedia.org
methadone, disopyramide, dronedarone irinotecan, lurasidone, colchicine alprazolam, oral midazolam, oral triazolam felodipine, ranolazine, tolvaptan, eplerenone HMG-CoA reductase inhibitors: lovastatin, simvastatin ergot alkaloids: ergotamine, dihydroergotamine, ergometrine, methylergometrine Others: cisapride, nisoldipine, dofetilide, pimozide The following medications are not recommended with ketoconazole:
Coma Potion (2008, Heartworm) Painted Nails (2008, Hospital) Electronic Dreams (2009, Heartworm) Easel and Ruby (2009, What's Your Rupture?) The Laurels (2009, Big Love Records) Death Comes Close (2009, Matador) Stars Explode (split with Prurient) (2010, Hospital) Life Magazine Remixes (2010, Matador) New Morale Leadership (2010, Hospital) Rebellion Is Over (collaboration with Genesis P-Orridge and Black Rain) (2015, Heartworm Press/Dais Records) You & Me & Infinity (2018, Heartworm Press) Fate in Seven Lessons (2021, Heartworm) Singles
=== Extraterrestrial === Beyond Earth, strong evidence suggests the presence of calcium carbonate on Mars. Signs of calcium carbonate have been detected at more than one location (notably at Gusev and Huygens craters). This provides some evidence for the past presence of liquid water.
Using the co-ordinates of the subunits and segments to determine the topographic location of the defect on the nose, the plastic surgeon plans, maps, and executes a rhinoplasty procedure. The unitary division of the nasal topography permits minimal, but precise, cutting, and maximal corrective-tissue coverage, to produce a functional nose of proportionate size, contour, and appearance for the patient. Hence, if more than 50 percent of an aesthetic subunit is lost (damaged, defective, destroyed) the surgeon replaces the entire aesthetic segment, usually with a regional tissue graft, harvested from either the face or the head, or with a tissue graft harvested from elsewhere on the patient's body.
Sources: en.wikipedia.org
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.
Published work usually examines actin binding, cell migration and tissue repair endpoints in cell and animal models. Findings are generally described as preliminary, and controlled human data remain limited.
Because TB-500 is a trade name rather than a chemical identifier, different vendors and papers may attach it to different fragment lengths. Checking the stated sequence is the practical way to resolve the ambiguity.
Sealed, dry and protected from light at reduced temperature is the usual laboratory convention. Allowing a cold vial to reach room temperature before opening limits condensation. Repeated opening exposes the powder to moisture and should be minimised.