actin-binding motif 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.
Updated 2025-09-21. Numbers and descriptions here follow the published literature rather than marketing material.
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.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Molecular formula | C38H68N10O14 | Acetylated heptapeptide form |
| Monoisotopic mass | 888.5 Da | Average mass about 889 Da |
| Appearance | White to off-white solid | Usually supplied as lyophilised powder |
| Solubility class | Highly water soluble | Also dissolves in aqueous buffers |
| Common synonyms | Tbeta4 fragment, thymosin beta-4 (17-23) | Refer to the same sequence |
TB-500 is a synthetic peptide whose sequence corresponds to a short fragment near the N-terminus of thymosin beta-4, a small protein present in most mammalian cells. The fragment is commonly cited as containing the actin-binding region of the parent molecule, which is why it appears in laboratory work on cell migration and tissue repair. Suppliers distribute it as a lyophilised powder intended for research use. Its identity is defined by amino acid sequence and by the presence of an acetyl group on the N-terminal residue.
Full-length thymosin beta-4 consists of roughly forty-three amino acids and ranks among the more abundant small proteins in the cytoplasm. The fragment is much shorter, so it cannot reproduce every function attributed to the intact molecule. In cell culture, short actin-binding motifs can interfere with filament dynamics and cell movement, but such observations come from controlled experiments rather than from whole-animal work. Whether a truncated fragment produces the same effects as the parent protein remains an open question.
Interest in the peptide grew during the 2000s and 2010s, when studies of tendon and ligament injuries in horses reported changes in lesion size after treatment. Those reports circulated widely outside the scientific literature and shaped much of the current online discussion. Subsequent reviews noted inconsistent study design, small groups, and a shortage of independent replication. Popular descriptions often blur the line between the fragment, the complete protein, and unrelated growth factors, which complicates comparisons across sources.
TB-500 is a synthetic peptide preparation marketed under a name derived from thymosin beta-4, a 43-residue actin-binding protein first isolated from thymus tissue. The full-length protein has a reported molecular mass near 4963 Da, while material sold as TB-500 is often described as a fragment containing the actin-binding motif LKKTETQ. Because suppliers use the name inconsistently, published sources sometimes refer to the same label as a fragment, a synthetic copy, or a related analog. This naming ambiguity complicates direct comparison of reports across studies.
Laboratory work on thymosin beta-4 describes binding to monomeric actin and effects on cell migration, angiogenesis, and inflammatory signaling in cultured cells. Animal models have examined skin, corneal, and cardiac repair after injury, with outcomes reported mainly in preclinical literature. Most of that evidence concerns the parent protein rather than preparations labelled TB-500, so extrapolation from animal findings to a specific commercial product remains uncertain. Whether the two behave identically in living systems has not been established in controlled human studies.
No major regulatory agency has approved TB-500 for therapeutic use, and it holds no pharmacopoeial monograph. The name appears on the World Anti-Doping Agency prohibited list within the class covering peptide hormones, growth factors, and related substances. Detection in doping control relies on mass spectrometric methods applied to urine, often after preparation steps that concentrate the analyte. Discussion of TB-500 therefore clusters in biochemistry, sports medicine, and anti-doping literature rather than in registered clinical trials.
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.
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== Applications of peptide microarrays == Peptide microarrays can be used to study different kinds of protein-protein interactions, specially those involving modular protein substructures called peptide recognition modules or, most commonly, protein interaction domains. The reason for this is that such protein substructures recognize short linear motifs often exposed in natively unstructured regions of the binding partner, such that the interaction can be modelled in vitro by peptides as probes and the peptide recognition module as analyte. Most publications can be found in the context of immune monitoring and enzyme profiling.
==== κ-opioid receptor ==== In 1997, a group of Australian researchers proposed (based on a study in rats) that oxycodone acts on KORs, unlike morphine, which acts upon MORs. Further research by this group indicated the drug appears to be a high-affinity κ2b-opioid receptor agonist. However, this conclusion has been disputed, primarily on the basis that oxycodone produces effects that are typical of MOR agonists. In 2006, research by a Japanese group suggested the effect of oxycodone is mediated by different receptors in different situations. Specifically in diabetic mice, the KOR appears to be involved in the antinociceptive effects of oxycodone, while in nondiabetic mice, the μ1-opioid receptor seems to be primarily responsible for these effects.
Seizures Haemorrhage † Myelosuppression, including: thrombocytopenia, anaemia, neutropenia and lymphopenia, in descending order of frequency. Omacetaxine mepesuccinate can cause fetal harm when administered to a pregnant woman. Women using HHT should avoid becoming pregnant and also avoid nursing while receiving HHT.
Sources: en.wikipedia.org
It was never resolved. By the close of the 1960s, the US and the UK had turbofans with bypass ratios of 4 or 5 to 1. The first Soviet large turbofan, the Lotarev D-18T, did not appear before the mid-1980s. The Soloviev D-30, originally intended for the Il-86, was the most advanced Soviet civil aeroengine. It had a bypass ratio of 2.4 to 1 and aerodynamic clamshell thrust reversers. It failed to attain the required thrust, however: "only after the lapse of three years that were spent on preparing the advanced development project did it become clear that these engines would not provide the necessary take-off performance." The less-advanced Kuznetsov NK-8 series engine, adopted on March 26, 1975, had a bypass ratio of 1.15 to 1 and drag-inducing grilles over its cascade thrust reversers. Both these engines had high specific fuel consumptions and were noisy. Being ultimate developments of smaller engines, they could not offer growth to future Il-86s. The appropriate/intermediate technology principles to which most Soviet airliners before the Il-86 had been designed meant that they had typically five-member flight crews. The design and entry into service in 1972 of the Tu-154, an airliner built to high technology principles (more automation, less human input), showed that Soviet science lagged behind in the development of avionics which would remove the need for navigators and radio operators. A programme of avionics development was mounted to enable the Il-86 to operate in most weather with a three-member flight crew, matching Western technology of the time.
The use of mAbs that specifically bind to carbohydrate epitopes of AGPs have also been employed to infer functions based on the location and pattern of the AGP epitopes. Commonly used mAb against AGPs include CCRC-M7, LM2, JIM8, JIM13 and JIM14. The function of individual AGPs has largely been inferred through studies of mutants. For example, the Arabidopsis root-specific AtAGP30 was shown to be required for in vitro root regeneration suggesting a function in regenerating the root by modulating phytohormone activity. Studies of agp6 and agp11 mutants in Arabidopsis have demonstrated the importance of these AGPs to prevent uncontrolled generation of the pollen grain and for normal growth of the pollen tube. The functional mechanisms of AGPs in cell signalling is not well understood. One proposed model suggests AGPs can interact and control the release of calcium from AG glycan (via GlcA residues) to trigger downstream signalling pathways mediated by calcium. Another possible mechanism, largely based on the study of FLAs, suggests the combination of fasciclin domain and AG glycans can mediate cell-cell adhesion.
The country had a 2019 Forest Landscape Integrity Index mean score of 5.95/10, ranking it 90th globally out of 172 countries. Some 3,700 plant species have been identified in the country, from which to date 23 have been declared natural monuments, 74 extinct, 39 endangered, 171 vulnerable, and 1,253 rare. The fauna of Romania consists of 33,792 species of animals, 33,085 invertebrate and 707 vertebrate, with almost 400 unique species of mammals, birds, reptiles, and amphibians, including about 50% of Europe's (excluding Russia) brown bears and 20% of its wolves. Romania is often seen by most as having the shape resembling one of a goldfish.
Sources: en.wikipedia.org
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.
It consists of leucine, lysine, lysine, threonine, glutamic acid, threonine, and glutamine in that order. The N-terminal leucine is usually acetylated in the forms described in catalogues.
Controlled human data is limited, and most published findings come from cell culture or animal work. This makes it difficult to state clinical effects with confidence.
The leading proposal involves sequestration of monomeric actin, which would alter cytoskeletal turnover and cell movement. The actin-binding motif shared with the parent protein is central to that idea. Direct confirmation in whole organisms remains limited.