The short version of thymosin beta-4 fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2026-05-18. Anything still debated is marked as such rather than presented as settled.
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.
TB-500 is a research peptide whose sequence matches residues 17 to 23 of thymosin beta-4, a 43-residue protein present in most mammalian cells. The chain is seven amino acids long, written as LKKTETQ, and is normally supplied with an acetyl group on the N-terminus. Suppliers list it as a lyophilised powder under the code name TB-500, and the same sequence appears elsewhere in catalogues as the thymosin beta-4 actin-binding fragment. The label is commercial rather than systematic, so no single authority fixes exactly what TB-500 denotes.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Appearance | White to off-white powder | Supplied as a lyophilised cake in sealed vials |
| Solubility class | Freely soluble in water | Polar and charged side chains dominate the sequence |
| Typical storage temperature | -20 °C or below | Dry and dark; a desiccant is often recommended |
| Identity confirmation | Mass spectrometry | Observed mass compared with the theoretical value |
| Common synonyms | Thymosin beta-4 fragment | Also written as T beta 4 fragment 17-23 |
Reconstitution practices affect downstream measurements. The dry powder is typically dissolved in sterile water or a suitable aqueous buffer, then mixed gently rather than vortexed at high speed. Visible particles or cloudiness suggest incomplete dissolution or contamination and should be investigated. For long-term storage, aliquots should be labeled with concentration, solvent, and date. Open questions include how different buffers alter peptide conformation and whether specific container materials adsorb the peptide. Those variables can change apparent concentration in assays even when the chemical identity is correct.
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.
The fragment most often associated with the name carries the sequence Ac-LKKTETQ, matching residues 17 through 23 of thymosin beta-4. That region holds the actin-binding motif responsible for much of the parent protein's biochemical activity. Apart from N-terminal acetylation the peptide is unmodified and contains no disulfide bonds, so it shows little ordered secondary structure in solution. Full-length thymosin beta-4 is instead a 43-residue polypeptide of roughly 4.9 kDa found widely across mammalian cell types.
Material sold under this label typically arrives as a freeze-dried powder in a sealed vial with a certificate of analysis. Such certificates usually report reversed-phase chromatography purity plus a mass confirmation, and stated purities commonly sit between 95 and 99 percent. Counter-ion identity, residual trifluoroacetate, water content, and peptide net weight are separate specifications that a certificate may or may not include. A purity figure alone does not establish sequence identity, so independent mass verification remains the practical check.
Some analysts used the term to describe the worsening relations between Russia on one side and the West or NATO, or more specifically the United States on the other since the 2014 Russian annexation of Crimea and intervention in Eastern Ukraine, which started the Russo-Ukrainian war. Others argue that the term is not appropriate.
=== Drew Holt === Andrew "Drew" Holt (Miles Heizer) is Sarah's son, age 14 at the beginning of the series. He is characterized as sensitive and longs for a male role model. Brief glimpses of Seth (Drew's absentee father) and statements by Sarah indicate that Drew has suffered much disappointment at the hands of his dad. As a result, he has become sullen and withdrawn. Drew regularly seeks romantic advice from the male figures in his life, Zeek and Adam. Drew plays baseball in the first two seasons, with Adam's help, and shows Max how to catch a fly ball. During the third season, Drew develops a relationship with Amy, a girl introduced to him by his grandfather during a yard sale. The relationship with his new girlfriend, Amy, helps him to become less aloof and break the shell of his social inhibitions. He is shown having trouble adjusting to his mother's relationship with Mark Cyr, a teacher at his high school. In the season three finale, Drew and Amy sleep together for the first time, while his family celebrates Crosby and Jasmine's wedding outside. During the beginning of the fourth season, Amy breaks up with Drew after meeting someone else over the summer. They try to stay friends, but later get back together after Amy learns of his aunt's cancer. They are caught having sex by Mark, who tells Drew's mother. Amy eventually ends up pregnant. She, however, has an abortion and decides it is best for her to stay single. At the end of season four, Drew is accepted into the University of California, Berkeley.
=== Food packaging === A good food packaging material should be able to block out microbes (to prevent spoiling and foodborne illness) and prevent oxygen from entering (to prevent rancidity). Depending on the product, it may be also desirable to stop water vapor from going across (to maintain crispness or wetness), to block out light and ultraviolet, and/or be resistant to rough handling. Classical plastic-based materials satisfy these criteria, but they are not biodegradable and create a trash problem. Among biodegradable options, chitosan films and chitosan composite films come closest to fulfilling all of these goals. Chitosan also has an intrinsic antimicrobial activity, which could potentially provide an extra line of defense to microbes.
== Structural studies == As of late 2007, 7 structures have been solved for this class of enzymes, with PDB accession codes PDB: 1AFS, PDB: 1FJH, PDB: 1FK8, PDB: 1LWI, PDB: 1RAL, PDB: 2DKN, and PDB: 2FVL.
Sources: en.wikipedia.org
==== Immunological biosensor ==== Gold nanoparticles have been coated with peptides and glycans for use in immunological detection methods. The possibility to use glyconanoparticles in ELISA was unexpected, but the method seems to have a high sensitivity and thus offers potential for development of specific assays for diagnostic identification of antibodies in patient sera.
Jamal al-Husayni Tewfiq al-Husayni Yusif Sahyun Kamil al-Dajani Emile al-Ghury Rafiq al-Tamimi and Anwar al-Khatib (all members of or affiliated with the Palestine Arab Party) Izzat Tannous (an independent Christian medical doctor) Antone Attallah (a member of the Greek Orthodox community) Ahmad al-Shukayri (a lawyer from Acre and an Arab nationalist) Sami Taha – head of Palestine Arab Workers Society Yousef Haikal (the mayor of Jaffa, who was politically independent) The Istiqlal Party and other nationalist groups objected to these moves, and formed a rival Arab Higher Front. In May 1946, the Arab League ordered the dissolution of the AHC and Arab Higher Front and formed a five-member Arab Higher Executive, under Amin al-Husayni's chairmanship, and based in Cairo. The new AHE consisted of:
=== Toxicity === Although selenium is an essential trace element, it is toxic if taken in excess. Exceeding the Tolerable Upper Intake Level of 400 micrograms per day can lead to selenosis. This 400 microgram (μg) Tolerable Upper Intake Level is based primarily on a 1986 study of five Chinese patients who exhibited overt signs of selenosis and a follow-up study on the same five people in 1992. The 1992 study actually found the maximum safe dietary Se intake to be approximately 800 micrograms per day (15 micrograms per kilogram body weight), but suggested 400 micrograms per day to not only avoid toxicity, but also to avoid creating an imbalance of nutrients in the diet and to account for data from other countries. In China, people who ingested corn grown in extremely selenium-rich stony coal (carbonaceous shale) have suffered from selenium toxicity. This coal was shown to have selenium content as high as 9.1%, the highest concentration in coal ever recorded in literature. Symptoms of selenosis include a garlic odor on the breath, gastrointestinal disorders, hair loss, sloughing of nails, fatigue, irritability, and neurological damage. Extreme cases of selenosis can result in cirrhosis of the liver, pulmonary edema, and death. Elemental selenium and most metallic selenides have relatively low toxicities because of their low bioavailability. By contrast, selenates and selenites are very toxic, having an oxidant mode of action similar to that of arsenic trioxide. The chronic toxic dose of selenite for humans is about 2400 to 3000 micrograms of selenium per day for a long time.
Anti-metabolites are a group of molecules that impede DNA and RNA synthesis. Many of them have a similar structure to the building blocks of DNA and RNA. The building blocks are nucleotides; a molecule comprising a nucleobase, a sugar and a phosphate group. The nucleobases are divided into purines (guanine and adenine) and pyrimidines (cytosine, thymine and uracil). Anti-metabolites resemble either nucleobases or nucleosides (a nucleotide without the phosphate group), but have altered chemical groups. These drugs exert their effect by either blocking the enzymes required for DNA synthesis or becoming incorporated into DNA or RNA. By inhibiting the enzymes involved in DNA synthesis, they prevent mitosis because the DNA cannot duplicate itself. Also, after misincorporation of the molecules into DNA, DNA damage can occur and programmed cell death (apoptosis) is induced. Unlike alkylating agents, anti-metabolites are cell cycle dependent. This means that they only work during a specific part of the cell cycle, in this case S-phase (the DNA synthesis phase). For this reason, at a certain dose, the effect plateaus and proportionally no more cell death occurs with increased doses. Subtypes of the anti-metabolites are the anti-folates, fluoropyrimidines, deoxynucleoside analogues and thiopurines. The anti-folates include methotrexate and pemetrexed. Methotrexate inhibits dihydrofolate reductase (DHFR), an enzyme that regenerates tetrahydrofolate from dihydrofolate. When the enzyme is inhibited by methotrexate, the cellular levels of folate coenzymes diminish.
=== Using a metal salt and cyclopentadienyl reagents === Sodium cyclopentadienide (NaCp) is the preferred reagent for these types of reactions. It is most easily obtained by the reaction of molten sodium and dicyclopentadiene. Traditionally, the starting point is the cracking of dicyclopentadiene, the dimer of cyclopentadiene. Cyclopentadiene is deprotonated by strong bases or alkali metals.
Sources: en.wikipedia.org
No. Thymosin beta-4 is a 43-residue protein, while TB-500 matches only residues 17 to 23 of that chain. The two are related but differ in size, and a method that identifies one does not automatically identify the other.
It corresponds to the actin-binding region of thymosin beta-4. Commercial synthesis reproduces that seven-residue stretch, usually with an acetyl group on the N-terminus.
It is not authorised as a medicine in the United States or the European Union and is distributed as a research chemical. Labels consequently carry research-use-only statements rather than clinical indications.
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.