This is a working overview of Thymosin beta-4, written for readers who want more than a one-paragraph summary but less than a textbook.
This page was last updated on 2025-07-23 and is reviewed periodically as new material appears.
TB-500 is a catalogue name applied to a synthetic peptide related to thymosin beta-4, an actin-binding protein found in most mammalian cells. Suppliers do not use the label consistently: some describe it as the full 43-residue protein, others as a short fragment from the actin-binding region, and others as a related tetrapeptide. Because the name is commercial rather than chemical, two products sold under it may not contain the same molecule. This naming ambiguity is the first point to check in any description of the material.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Appearance | White to off-white lyophilized powder | Typical form for short synthetic peptides |
| Solubility class | Freely soluble in water and aqueous buffer | Dissolution aided by gentle mixing, not vigorous shaking |
| Typical storage temperature | −20 °C, desiccated | −80 °C used for long-term holding |
| Common analytical method | Reverse-phase HPLC with UV detection near 214 nm | Identity confirmed separately by mass spectrometry |
| Common synonyms | Thymosin beta-4 fragment; TB4 fragment | Naming varies between suppliers and publications |
TB-500 is a synthetic seven-residue peptide whose sequence, LKKTETQ, matches the N-terminal actin-binding region of thymosin beta-4. It is usually supplied in an N-terminally acetylated form, a modification that blocks the free amino terminus and can influence behavior in solution. In the research literature the same sequence appears under several names, including thymosin beta-4 fragment and shortened thymosin beta-4. Because it is a short peptide rather than the full 43-residue parent protein, its measured properties differ from those reported for thymosin beta-4 as a whole, and the two are not interchangeable in experimental design.
Thymosin beta-4 itself is a small, widely expressed protein that sequesters monomeric actin and participates in cell migration, angiogenesis, and tissue repair. Researchers have examined the shortened fragment as a possible mimic of some of these activities, reasoning that the actin-binding motif lies within the first few residues. Binding to monomeric actin has been observed in cell-free systems. Whether the fragment reproduces the broader effects of the full protein in living tissue remains an open question, and findings from animal models are frequently cited without a clear bridge to human physiology.
Thymosin beta-4 was isolated from calf thymus in the early 1980s and later characterised as an abundant intracellular actin-sequestering protein. Interest in short synthetic fragments grew once the actin-binding motif had been mapped to the middle of the sequence. TB-500 came out of that line of work as a truncated analogue rather than a natural isolate, and it is now sold mainly to laboratories. Published studies on the fragment have been largely in vitro or in animal models, and controlled human trials remain sparse, so claims about effects in people rest on extrapolation.
Literature and online discussion often conflate TB-500 with full-length thymosin beta-4, even though the two differ in size and are not interchangeable in analytical terms. The fragment is produced by solid-phase peptide synthesis, and the product is a defined seven-residue chain rather than a biological extract. Because the term is a trade-style label, two vendors may supply materials of the same nominal sequence but different counter-ion content, purity, or water content. Comparisons across studies are therefore difficult unless the exact sequence and purity are reported.
The regulatory position is broadly consistent across major jurisdictions: no thymosin beta-4 fragment is an approved medicine, and laboratory material is commonly labelled as not intended for human consumption. Anti-doping rules in sport list thymosin beta-4 and its fragments among prohibited peptide hormones. Because these products travel through research-chemical channels rather than pharmaceutical supply chains, quality varies considerably between vendors. Independent testing of identity, purity and sterility is the only dependable check, and a certificate of analysis describes one batch rather than a supplier's whole catalogue.
Lyophilized peptide powder is normally held desiccated at −20 °C, with −80 °C used for longer storage periods. Allowing a sealed vial to reach room temperature before opening is standard practice, because condensation forming on cold powder introduces moisture. Once dissolved, solutions are typically kept cold and shielded from light. Repeated freeze-thaw cycles are avoided because they encourage aggregation and gradual loss of material. These conventions are general to synthetic peptides rather than unique to any one sequence.
Purity and identity are separate measurements and are often confused. Reverse-phase high-performance liquid chromatography, usually with ultraviolet detection near 214 nanometres, reports the share of total peak area belonging to the target compound. Mass spectrometry by electrospray or matrix-assisted laser desorption then checks whether the observed mass matches the expected sequence. Neither measurement alone shows that a vial holds the intended peptide. Peptide content, meaning the fraction of vial mass that is genuine peptide rather than counter-ion, water or residual acid, is reported separately and is frequently lower than the stated purity figure.
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.
Ajinomoto Co., Inc. (味の素株式会社, Ajinomoto kabushiki gaisha; Japanese pronunciation: [a.(d)ʑi.noꜜ.mo.to]) is a Japanese multinational food and biotechnology corporation which produces seasonings, cooking oils, frozen foods, beverages, sweeteners, amino acids, insulating films, and pharmaceuticals. Aji-No-Moto (味の素, "essence of taste") is the trade name for the company's original monosodium glutamate (MSG) product, the first of its kind, since 1909. The corporation's head office is located in Chūō, Tokyo. As of 2024, Ajinomoto operates in 31 countries worldwide and employs an estimated 34,862 people. Its yearly revenue in 2024 is around ¥1.53 trillion JPY or $10.61 billion USD.
The former republics were transformed into the British colonies of the Transvaal and Orange River, and in 1910 were merged with the Natal and Cape Colonies to form the Union of South Africa, a self-governing colony within the British Empire. British expeditionary efforts were aided significantly by colonial forces from the Cape Colony, the Natal, Rhodesia, and many volunteers from the British Empire. Native African recruits contributed increasingly to the British effort. International public opinion was sympathetic to the Boers and hostile to the British. Even within the UK, there existed significant opposition to the war. As a result, the Boer cause attracted volunteers from neutral countries, including the German Empire, the United States, Russia and parts of the British Empire, such as Australia and Ireland. Some consider the war the beginning of questioning the British Empire's global dominance, due to the war's surprising duration and unforeseen losses suffered by the British. A trial for British war crimes, including the killings of civilians and prisoners of war, was opened in January 1902. The war had a lasting effect on the region and on British domestic politics.
Also known as mediastinal emphysema to divers, pneumomediastinum is a volume of gas inside the mediastinum, the central cavity in the chest between the lungs and surrounding the heart and central blood vessels, usually formed by gas escaping from the lungs as a result of lung rupture. Gas bubbles escaping from a ruptured lung can travel along the outside of bronchioles and blood vessels until they reach the mediastinal cavity round the heart, major blood vessels, oesophagus and trachea. Gas trapped in the mediastinum expands as the diver continues to rise. The pressure of the trapped gas may cause intense pain inside the rib cage and in the shoulders, and the gas may compress the respiratory passageways, making breathing difficult, and collapse blood vessels. Symptoms range from pain under the sternum, shock, shallow breathing, unconsciousness, respiratory failure, and associated cyanosis. The gas will usually be absorbed by the body over time, and when the symptoms are mild, no treatment may be necessary. Otherwise it may be vented through a hypodermic needle inserted into the mediastinum. Recompression is not usually indicated.
Sources: en.wikipedia.org
Larson received media attention for scolding members of Congress for shutting down the government on September 30, 2013. Larson was among the 46 Democrats who voted against final passage of the Fiscal Responsibility Act of 2023 in the House.
=== Selected articles === Adler, V., Yin, Z., Fuchs, S. Y., Benezra, M., Rosario, L., Tew, K. D., ... & Ronai, Z. E. (1999). Regulation of JNK signaling by GSTp. The EMBO journal, 18(5), 1321–1334. Townsend, D. M., Tew, K. D., & Tapiero, H. (2003). The importance of glutathione in human disease. Biomedicine & pharmacotherapy, 57(3-4), 145–155. Townsend, D. M., & Tew, K. D. (2003). The role of glutathione-S-transferase in anti-cancer drug resistance. Oncogene, 22(47), 7369–7375. Tapiero, H., & Tew, K. D. (2003). Trace elements in human physiology and pathology: zinc and metallothioneins. Biomedicine & Pharmacotherapy, 57(9), 399–411. Hayes, J. D., Dinkova-Kostova, A. T., & Tew, K. D. (2020). Oxidative stress in cancer. Cancer cell, 38(2), 167–197. Tew, K.D. Alkylating Agents. In: Principles & Practice of Oncology. Eds. DeVita, Hellman & Rosenberg. pp246–256, 2018. Tew, K.D. Protein S-Glutathionylation & Glutathione S-transferase P. In: Glutathione. Editor: Leopold Flohé. CRC Press. Chapter 12, 201–214, 2018.
== Regulation of mRNA stability == Pin1, a parvulin, regulates mRNA stability and expression in certain eukaryotics mRNAs. These mRNAs are GM-CSF, Pth, and TGFβ and each of them have AREs, or AU-rich cis-elements. The ARE binding protein KSRP has a Pin1 binding site. Pin1 binds to this site and dephosphorylates the serine and isomerizes the peptide bond between Ser181 and Pro182. This isomerization causes the decay of Pth mRNA. KSRP, and other ARE binding proteins like AUF1, are thought to affect the other mRNAs through mechanisms similar to Pth, with the requirement of a phosphorylated serine bonded to a proline in a specific conformation. Pin1 also triggers proline isomerization of Stem-Loop Binding Protein (SLBP), allowing it to control the dissociation of SLBP from histone mRNA. This leads to Pin1 being able to affect histone mRNA decay. Pin1 affects many other genes in the form of gene silencing through the disruption of cell pathways, making it important in mRNA turnover by modulating RNA binding protein activity.
Sources: en.wikipedia.org
TB-500 is a trade-style label for a synthetic peptide connected to thymosin beta-4. It is sold mainly through research-chemical channels and is not a single chemically defined product across suppliers.
Not necessarily. Some vendors use the name for the full 43-residue protein, while others apply it to a short actin-binding fragment or to a related tetrapeptide. The sequence should be confirmed from documentation rather than assumed from the label.
No thymosin beta-4 fragment holds marketing approval as a medicine in major jurisdictions. Material offered for sale is typically labelled for laboratory research only.
No. TB-500 is a short synthetic peptide matching residues 17 to 23 of thymosin beta-4, while the parent protein contains 43 residues. The fragment lacks the rest of the protein sequence, so the two are related but not identical.