TB-500 raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
Reviewed 2026-02-09. Anything still debated is marked as such rather than presented as settled.
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.
Once dissolved, the peptide is far less stable than the dry powder. Aqueous solutions are subject to hydrolysis, oxidation at susceptible residues and gradual loss of material through adsorption onto glass and plastic surfaces. Terminal glutamine can cyclise under some conditions, producing a related species that complicates purity assessment. Dilute solutions tend to lose a larger fraction of material to surfaces than concentrated ones. Buffers, pH and ionic strength all influence the rate of change, so stability figures are only meaningful when those parameters are stated alongside the storage interval.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Appearance | White to off-white solid | Lyophilised cake or powder |
| Solubility class | Freely soluble in water | Aqueous buffers also used |
| Typical storage temperature | About -20 degrees Celsius | Dry, sealed and protected from light |
| Typical analytical method | Reversed-phase HPLC or LC-MS/MS | Used for purity, identity and quantification |
| Common synonyms | Thymosin beta-4 fragment | Also listed under fragment-based descriptions |
Discussion of the compound frequently appears alongside other short peptides described as fragments of larger proteins. That grouping is convenient but can be misleading, because fragment length, charge, and modification state determine how a peptide behaves in solution and in any experimental system. A seven-residue acetylated peptide and a full-length protein differ in mass by roughly an order of magnitude, and they cannot be assumed to share distribution or binding properties. Precision about which molecule is under discussion is the single most useful step when reading such material.
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.
Sports authorities classify the peptide as a prohibited substance, and it appears on the World Anti-Doping Agency list under peptide hormones, growth factors, and related substances. Racing jurisdictions for horses and dogs have issued separate restrictions, and several national bodies treat it as a controlled or prescription-only item. As a research chemical it is sold without a therapeutic indication, and labels usually state that the product is not for human or veterinary use. Regulatory treatment therefore varies by country.
Detection in biological matrices generally relies on liquid chromatography coupled with tandem mass spectrometry, because the peptide lacks a convenient ultraviolet chromophore beyond the amide backbone. Immunoassays have been described, but antibodies raised against the fragment can cross-react with the full-length protein or with unrelated peptides, so findings usually require confirmation by a second technique. Sample preparation typically involves protein precipitation followed by solid-phase extraction. Reported detection windows depend on dose, route, matrix, and instrument sensitivity.
Interest in the compound comes largely from studies of the parent protein, which participates in actin sequestration, cell migration and tissue repair processes. Whether a short fragment reproduces those activities is a separate question that remains open in the published record. Many summaries describe mechanisms by analogy to thymosin beta-4 rather than from direct measurements on the fragment. Claims about activity should be treated as provisional unless a cited study specifies the exact peptide, its purity and the assay used.
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.
Controlled human trials of the short fragment are scarce. Much of what appears in review articles is extrapolated from animal models or from studies of the parent protein, and literature searches return a larger body of cardiac and ophthalmic work on thymosin beta-4 than on the abbreviated peptide. Regulatory treatment differs by jurisdiction, and in several countries the material is handled as a research chemical rather than an approved therapeutic. Statements about human benefit should be read as provisional.
Biological interest in this peptide centers on its relationship to actin dynamics. Thymosin beta-4 binds monomeric actin through an LKKTET motif, and a short sequence carrying that motif can compete with other actin-binding proteins in cell-free preparations. Investigators propose that such competition shifts the balance between filament assembly and disassembly, which in turn affects how readily a cell extends protrusions and migrates. Most of the supporting observations come from cultured cells and purified protein systems rather than from intact organisms.
Animal work has examined the peptide in models of cardiac injury, skin wounding, and corneal repair, with reported outcomes covering cell migration, inflammatory cell influx, and tissue remodeling. Several of those experiments used the full-length protein or longer fragments instead of the seven-residue sequence, which makes direct comparison between reports difficult. Results are generally described as tissue-dependent, and effect sizes vary considerably across laboratories. Independent replication is uneven, so the overall picture is incomplete rather than settled.
=== Active site === Histidinol is held inside the active site thanks to a zinc ion, but the zinc ion does not participate in the catalysis otherwise. The zinc ion is held in place by His262, Gln259, Asp360 and His419 (which, in homodimeric histidinol dehydrogenases, comes from the other monomer). Histidinol itself is held in place by His327 and His367 from one moment unit and Glu414 from the other monomer unit. A Cys residue has been implicated in the catalytic mechanism of the second oxidative step. However, according to newer studies with histidinol dehydrogenase from E. coli, the mechanism is catalyzed by four bases, B1-B4. His327 acts as the first base, deprotonating histidinol's hydroxyl group. Concomitantly, hydride is abstracted from histidinol by NAD+, which is then exchanged for a second NAD+ molecule. Glu325 acts as the second base, deprotonating a molecule of water, which then attacks histidinol. At the same time, His327 (now protonated) donates a proton to the aldehydic oxygen, which results in a gem-diol. After then, His327 again deprotonates one of the hydroxyl groups and NAD+ abstracts a proton from the reactive carbon atom. This series of steps oxidizes the hydroxyl group to a carboxylic acid.
Due to a series of German victories on the Eastern Front, the area of Congress Poland became occupied by the Central Powers of Germany and Austria; Warsaw was captured by the Germans on 5 August 1915. In the Act of 5th November 1916, a fresh incarnation of the Kingdom of Poland (Królestwo Regencyjne) was proclaimed by Germany and Austria on formerly Russian-controlled territories, within the German Mitteleuropa scheme. The sponsor states were never able to agree on a candidate to assume the throne, however; rather, it was governed in turn by German and Austrian governor-generals, a Provisional Council of State, and a Regency Council. This increasingly autonomous puppet state existed until November 1918, when it was replaced by the newly established Republic of Poland. The existence of this "kingdom" and its planned Polish army had a positive effect on the Polish national efforts on the Allied side, but in the Treaty of Brest-Litovsk of March 1918 the victorious in the east Germany imposed harsh conditions on defeated Russia and ignored Polish interests. Toward the end of the war, the German authorities engaged in massive, purposeful devastation of industrial and other economic potential of Polish lands in order to impoverish the country, a likely future competitor of Germany.
The latest version of the tequila standard (NOM-006-SCFI-2012) updated the standard to specify that the silver class of tequila cannot contain additives, to allow the aging time for the ultra-aged class to be displayed on the label, and to prohibit the selling of bulk tequila through vending machines, and required registering the agave during the calendar year of its plantation and required annual updates. In 2018, the Mexican government approved a proposal to celebrate the third Saturday of March as National Tequila Day.
"Machine Cleans Blood While You Wait"—1950 article on early use of dialysis machine at Bellevue Hospital New York City—an example of how complex and large early dialysis machines were Home Dialysis Museum—History and pictures of dialysis machines through time Introduction to Dialysis Machines—Tutorial describing the main subfunctions of dialysis systems. "First Nations man conducts own dialysis treatments to avoid move to the city"—CBC News (November 30, 2016)
Sources: en.wikipedia.org
== Redox activity == Most selenoproteins have a redox function analogous to proteins with Cys active sites. Two residues of Sec can be oxidized to form a diselenide bond (-Se-Se-), the selenium analog of the disulfide bridge. Sec can also form a selenenyl sulfide (-Se-S-) bond with Cys. The Se-H bond is more easily broken than the S-H bond, resulting in higher reactivity of the Sec residue compared to Cys. Also contributing to reactivity is the higher nucleophilicity, acidity, and leaving-group ability of selenolate (R-Se-) compared to thiolate (R-S-). The Se-Se bond is also weaker than the S-S bond. The result is that the Sec can easily be oxidized and reduced, without much change of getting stuck in one state. Sec is not more reactive than Cys in every single aspect. Selanyl radicals generated from Sec is less prone to attacking aromatic amino acid residues and protein Cα atoms than the thiyl radicals generated from Cys. This offers redox-active selenoproteins some protection from breaking itself apart compared to their cystine-only relatives.
TSAVLQ-SGFRK-NH2 and SGVTFQ-GKFKK are the two peptides corresponding to the two self-cleavage sites of the SARS 3C-like proteinase The protease is important in the processing of the coronavirus replicase polyprotein (P0C6U8). It is the main protease in coronaviruses and corresponds to nonstructural protein 5 (nsp5). It cleaves the coronavirus polyprotein at 11 conserved sites. The 3CL protease has a cysteine-histidine catalytic dyad at its active site. The sulfur of the cysteine acts as a nucleophile and the imidazole ring of the histidine as a general base.
1911 – Marie Sklodowska-Curie – discovery of radium & polonium 1935 – Irène Joliot-Curie – artificial radioactivity 1964 – Dorothy Crowfoot Hodgkin – protein crystallography 2009 – Ada E. Yonath – structure & function of the ribosome 2018 – Frances Arnold – directed evolution to engineer enzymes 2020 – Emmanuelle Charpentier and Jennifer Doudna – for CRISPR gene editing 2022 - Carolyn R. Bertozzi - for bioorthogonal chemistry Eight women have won the Nobel Prize in Chemistry (listed above), awarded annually since 1901 by the Royal Swedish Academy of Sciences. Marie Curie was the first woman to receive the prize in 1911, which was her second Nobel Prize (she also won the prize in physics in 1903, along with Pierre Curie and Henri Becquerel – making her the only woman to be award two Nobel prizes). Her prize in chemistry was for her "discovery of the elements radium and polonium, by the isolation of radium and the study of the nature and compounds of this remarkable element." Irene Joliot-Curie, Marie's daughter, became the second woman to be awarded this prize in 1935 for her discovery of artificial radioactivity. Dorothy Hodgkin won the prize in 1964 for the development of protein crystallography. Among her significant discoveries are the structures of penicillin and vitamin B12. Forty five years later, Ada Yonath shared the prize with Venkatraman Ramakrishnan and Thomas A. Steitz for the study of the structure and function of the ribosome.
== Montagnard influence == The working class was especially hurt by a hail storm which damaged grain crops in 1788, which caused bread prices to skyrocket. While the peasants of rural France could sustain themselves with their farms, and the wealthy aristocracy could still afford bread, the urban workers of France, the group that comprised the sans-culottes, suffered. In the city, the division grew between the sans-culottes and these wealthy aristocrats; the former had a particular hostility "towards those with large private incomes." The faction known as the Montagnards expressed concern for the working classes of France. When the National Convention met to discuss the fate of the former king Louis XVI in 1792, the sans-culottes vehemently opposed a proper trial, instead opting for an immediate execution. The moderate Girondin faction voted for a trial, but the radical Montagnards sided with the sans-culottes, deeming that a trial was not necessary, and won with a slim majority. Louis XVI was executed on January 21, 1793. The demands of the sans-culottes did not stop with the execution of the King, and the Montagnards worked hard to fulfil their mounting orders. This increased pressure from the radical masses exacerbated the ideological split between the Montagnards and the Girondins, and tensions began to grow within the convention. Eventually, by May 1793, the Montagnards worked with the National Guard—which was, at this time, mostly sans-culottes—to depose many of the Girondin deputies.
== Future == In May 2022, The Hollywood Reporter confirmed that Åkerlund would return to direct another film adaptation, The Black Kaiser, which its producers said would not be "a sequel or a prequel". Mikkelsen was set to reprise his role and co-write the screenplay with Jayson Rothwell, though it was later reported that only Rothwell was writing the film. One year later, Variety reported that Derrick Borte had replaced Åkerlund as director and that Hudgens would appear in the film. Filming was set to begin in the third quarter of 2023.
Sources: en.wikipedia.org
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.
Reported purity reflects the batch tested, the chromatographic method used and whether an independent laboratory performed the work. Values quoted without method detail or a traceable certificate are difficult to compare directly.
Short peptides are rapidly broken down by proteases and appear at low concentrations in urine, so the detection window is narrow. Sensitive extraction combined with tandem mass spectrometry is typically required.
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.