TB-500 is one of those subjects where the details matter more than the headlines. This page pulls together the background, the mechanisms, and the practical points readers ask about most.
Last reviewed on 2026-08-01. Where a claim depends on a specific study, the study is described rather than over-claimed.
Published research on the intact protein is substantial, covering actin regulation, cell migration, and wound models. Research using the heptapeptide fragment specifically is far smaller, and much of the circulating material originates in supplier documentation rather than peer-reviewed reports. Where fragment studies do exist, they often employ different sequences, chain lengths, or terminal modifications, which complicates direct comparison across papers. Readers encountering claims about TB-500 should therefore separate evidence about thymosin beta-4 from evidence about the fragment itself.
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.
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.
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 |
|---|---|---|
| Reported sequence | Ac-LKKTETQ | Described in most listings as the actin-binding region of thymosin beta-4 |
| Reported molecular weight | Approximately 889 Da | Value shifts with the stated sequence; compare against the certificate of analysis |
| Parent protein length | 43 amino acids | Thymosin beta-4; the fragment covers only a small part of it |
| Common synonyms | TB4 fragment; thymosin beta-4 fragment | Trade-style names rather than formal nomenclature |
| Formal monographs | Not established | Labeling conventions differ by supplier and region |
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.
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.
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.
=== Meniscus injury === A 2022 review found that in people with meniscus tears, PRP treatment reduced the failure rate of meniscus repair surgery and reduced postoperative pain. However, the review did not find consistent evidence that PRP improved knee function.
King Pellam, wounded by Balin (as in the Post-Vulgate). In the Vulgate's clearer Grail lineage, Pelles is the son of Pellehan and is wounded in a separate accident, while in the Post-Vulgate Pelles and Pellehan are brothers. The further step of mistaking them as the same character is understandable; Malory confuses the brothers Ywain and Ywain the Bastard, whom he eventually regards as the same character, after treating them as separate. King Pelles, grandfather of Galahad, described as "the maimed king". In one passage, he is explicitly identified with Pellam; in another, he is said to have suffered his wound under different circumstances. King Pescheour (or Petchere), lord of the Grail Castle, who never appears (at least, not under that name). He owes his existence to a mistake by Malory, who took the Old French roy peschour ("Fisher King", a phrase that Malory never otherwise uses) for a name rather than an epithet. Nevertheless, Malory treats him as distinct from Pelles. An anonymous, bedridden Maimed King, healed by Galahad at the climax of the Grail Quest. He is distinct from Pelles, who has just been sent out of the room, and who is, anyway, at least mobile. In addition, there is King Pellinore, Perceval's father (in other versions of the legend, Perceval is related to the Grail Kings line). It appears that Malory intended to have one Maimed King who was wounded by Balin and suffered until healed by his grandson Galahad, but he never successfully reconciled his sources.
=== Volatile organic compounds === Individual honeys from different plant sources contain over 100 volatile organic compounds (VOCs), which play a primary role in determining honey flavors and aromas. VOCs are carbon-based compounds that readily vaporize into the air, providing aroma, including the scents of flowers, essential oils, or ripening fruit. The typical chemical families of VOCs found in honey include hydrocarbons, aldehydes, alcohols, ketones, esters, acids, benzenes, furans, pyrans, norisoprenoids, and terpenes, among many others and their derivatives. The specific VOCs and their amounts vary considerably between different types of honey obtained by bees foraging on different plant sources. By example, when comparing the mixture of VOCs in different honeys in one review, longan honey had a higher amount of volatiles (48 VOCs), while sunflower honey had the lowest number of volatiles (8 VOCs). VOCs are primarily introduced into the honey from the nectar, where they are excreted by the flowers imparting individual scents. The specific types and concentrations of certain VOCs can be used to determine the type of flora used to produce monofloral honeys. The specific geography, soil composition and acidity used to grow the flora also have an effect on honey aroma properties, such as a "fruity" or "grassy" aroma from longan honey, or a "waxy" aroma from sunflower honey. Dominant VOCs in one study were linalool oxide, trans-linalool oxide, 2-phenylacetaldehyde, benzyl ethanol, isophorone, and methyl nonanoate.
Sources: en.wikipedia.org
Similar structures include the 310 helix (i + 3 → i hydrogen bonding) and the π-helix (i + 5 → i hydrogen bonding). The α-helix can be described as a 3.613 helix, since the i + 4 spacing adds three more atoms to the H-bonded loop compared to the tighter 310 helix, and on average, 3.6 amino acids are involved in one ring of α-helix. The subscripts refer to the number of atoms (including the hydrogen) in the closed loop formed by the hydrogen bond.
Antidotes are agents that can neutralise the effects of a poison or toxin. Antidotes counteract the effects of toxins in many ways, such as by blocking the absorption of the toxin, binding and neutralising the poison, opposing the toxin's end-organ function, or blocking the toxin's conversion to more hazardous metabolites. In addition to lowering the amount of free or active poison present, antidote delivery may also lessen the toxin's effects on organs through competitive inhibition, receptor blockage, or direct antagonistic interaction. The therapeutic index or ratio (TD50/ED50), which is the ratio of the toxic dosage (TD) or fatal dose (LD) to the effective dose (ED), determines the level of safety associated with a substance.
ISCOM technology was invented in 1982 by Professor Bror Morein at the Swedish University of Agricultural Sciences in Uppsala. The key components of ISCOMs are the Quillaja saponins, which are derived from the bark of the Chilean soap-bark tree Quillaja saponaria Molina. Quillaja saponins are well known for their ability to activate the immune system. It is also known that saponins in general can have toxic side-effects, including the induction of haemolysis. However, when Quillaia saponins, cholesterol and phospholipids are mixed under the specific stoichiometry that forms ISCOMs, this haemolytic activity is practically eliminated, while the adjuvant activity is retained.
The impact of this ~10 km asteroid massively altered the 187Os/188Os signature of marine sediments at that time - the average extraterrestrial 187Os/188Os of ~0.13 and the huge amount of Os this impact contributed (equivalent to 600,000 years of present-day riverine inputs) lowered the global marine 187Os/188Os value of ~0.45 to a minimum of ~0.2. Os isotope ratios may also be used as a signal of anthropogenic impact. The same 187Os/188Os ratios that are common in geological settings may be used to gauge the addition of anthropogenic Os through things like catalytic converters. While catalytic converters have been shown to drastically reduce the emission of NOx and CO, they are introducing platinum group elements (PGE) such as Os, to the environment. Other sources of anthropogenic Os include combustion of fossil fuels, smelting chromium ore, and smelting of some sulfide ores. In one study, the effect of automobile exhaust on the marine Os system was evaluated. Automobile exhaust 187Os/188Os has been recorded to be ~0.2 (similar to extraterrestrial and mantle derived inputs). The effect of anthropogenic Os can be seen best by comparing aquatic Os ratios and local sediments or deeper waters. Surface waters thought to be affected have depleted values compared to deep ocean and sediments by a ratio larger than can be explained by cosmic inputs. The alpha decay of 184Os into 180W (with a rate perhaps large enough for detection) has been proposed as a radiometric dating method for osmium-rich rocks or for differentiation of a planetary core.
Sources: en.wikipedia.org
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.
No. Thymosin beta-4 is a protein of 43 amino acids, while TB-500 is described as a short fragment of it. The two differ in size, structure, and the range of interactions each can support.
Naming for research peptides is not centrally coordinated, so vendors set their own labels and specifications. Differences in stated sequence, molecular weight, or purity documentation usually trace back to those independent labeling choices.
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.