actin binding comes up often in conversation and rarely with the context attached. Here we lay out the basics in order, then work through the practical considerations.
Last reviewed on 2026-06-16. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
TB-500 is a synthetic heptapeptide with the sequence Ac-LKKTETQ. It corresponds to a short N-terminal region of thymosin beta-4, a 43-amino-acid protein found in many cell types. The fragment contains an actin-binding motif, which is one reason it appears in laboratory studies of cell migration and cytoskeletal dynamics. TB-500 is not the full-length protein and is produced as a research chemical rather than an approved therapeutic agent. Its molecular weight is approximately 889 Da.
Several names appear in scientific and commercial contexts for this peptide. The label TB-500 is informal and does not follow standard biochemical nomenclature. Research articles more often describe the compound as a thymosin beta-4 fragment, Tβ4 fragment, or by its sequence Ac-LKKTETQ. Confusing TB-500 with full-length thymosin beta-4 can lead to incorrect assumptions about activity because the fragment lacks the remaining residues of the parent protein. The relationship between fragment and parent protein remains an active area of study.
| Property | Value | Notes |
|---|---|---|
| Common synonyms | Thymosin beta-4 fragment; TB4 fragment | Naming is inconsistent across suppliers and publications |
| Reported sequence | Ac-LKKTETQ | Corresponds to residues 17-23 of the parent protein |
| Frequently cited registry number | 77591-33-4 | Associated with full-length thymosin beta-4 rather than the fragment |
| Common supplied form | Freeze-dried solid | Often presented as an acetate or trifluoroacetate salt |
| Regulatory treatment | Varies by country | Frequently handled as a research chemical; not broadly approved as a therapeutic |
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.
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.
Storage recommendations center on keeping the dry powder cold, dry, and dark. A freezer at -20 degrees Celsius or below is conventional, and desiccant is often included to limit moisture uptake. Once dissolved, the peptide is less stable, and solutions are typically kept frozen and thawed only once. Repeated freeze-thaw cycles are a common source of losses because they promote aggregation and adsorption to container surfaces. Working aliquots are therefore prepared in advance, and glass or low-binding plastic is usually preferred over ordinary laboratory plastic.
Identity and purity are assessed with a small set of standard techniques. Reverse-phase high-performance liquid chromatography gives a purity estimate from peak area, usually recorded at 214 or 220 nanometers, where the peptide bond absorbs. Mass spectrometry confirms the expected molecular mass and can reveal truncated or oxidized species. Amino acid analysis or tandem mass spectrometry sequencing can verify the sequence itself. Additional quality attributes include water content, residual trifluoroacetic acid carried over from purification, and endotoxin where the material is intended for biological work.
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.
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.
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==== Medal of the Royal Victorian Order (RVM) ==== In Silver John Nelson Hart, Gamekeeper, Sandringham Estate. Keith Hodson, Stud Hand, Royal Studs. Constable Anthony Claud James, Royalty and Diplomatic Protection Department, Metropolitan Police. John Trodden Kerr, Leading Palace Attendant, Windsor Castle. Leading Marine Engineering Mechanic (Mechanical) Andrew Kevin King, HM Yacht Britannia. Richard Clive Lines, Painter, Sandringham Estate. Musician William Huw Morris, HM Yacht Britannia. Sergeant Paul Andrew George Murrell, Norfolk Constabulary. Peter Leonard Riches, Foreman Gardener, Crown Estate, Windsor. Constable Mervyn John Shrubb, Royalty and Diplomatic Protection Department, Metropolitan Police. David Wetherill, Sacristan, St George's Chapel, Windsor Castle. John Herbert Willison, lately of Truefitt & Hill Limited. Acting Petty Officer Marine Engineering Mechanic (Electrical) Barry John Winstone, HM Yacht Britannia.
Polycyclic aromatic hydrocarbons are tar components produced by pyrolysis in smoldering organic matter and emitted into smoke. Several of these PAH's are already toxic in their normal form, however, many of them can become more toxic to the liver. Due to the hydrophobic nature of PAH's they do not dissolve in water and are hard to expel from the body. In order to make the PAH more soluble in water, the liver creates an enzyme called Cytochrome P450 which adds an additional oxygen to the PAH, turning it into a mutagenic epoxide, which is more soluble but also more reactive. The first PAH to be identified as a carcinogen in tobacco smoke was benzopyrene, which been shown to toxicate into a diol epoxide and then permanently attach to nuclear DNA, which may either kill the cell or cause a genetic mutation. The DNA contains the information on how the cell functions; in practice, it contains the recipes for protein synthesis. If the mutation inhibits programmed cell death, the cell can survive to become a cancer, a cell that does not function like a normal cell. The carcinogenicity is radiomimetic, i.e. similar to that produced by ionizing nuclear radiation. Tobacco manufacturers have experimented with combustionless vaporizer technology to allow cigarettes to be consumed without the formation of carcinogenic benzopyrenes. Acrolein is a pyrolysis product that is abundant in cigarette smoke. It gives smoke an acrid smell and an irritating, tear-causing effect and is a major contributor to its carcinogenicity.
Sources: en.wikipedia.org
Microfilaments at the U.S. National Library of Medicine Medical Subject Headings (MeSH) Microfilament+proteins at the U.S. National Library of Medicine Medical Subject Headings (MeSH) "Microfilament" at Dorland's Medical Dictionary
He then divested the trade he controlled, as it would be more efficient and less likely to be brought down in one law enforcement swoop. He sent his lawyer to convene the nation's top drug traffickers at a house in Acapulco where he designated plazas or territories. The Tijuana route would go to his nephews, the Arellano Felix brothers. The Ciudad Juárez route would go to the Carrillo Fuentes family. Miguel Caro Quintero would run the Sonora corridor. Meanwhile, Joaquín Guzmán Loera and Ismael Zambada García would take over Pacific coast operations, becoming the Sinaloa Cartel. Guzmán and Zambada brought veteran Héctor Luis Palma Salazar back into the fold. The control of the Matamoros, Tamaulipas corridor—then becoming the Gulf Cartel—would be left undisturbed to its founder, Juan García Ábrego, who was not a party to the 1989 pact. Félix Gallardo still planned to oversee national operations, as he maintained important connections, but he would no longer control all details of the business. When he was transferred to a high-security prison in 1993, he lost any remaining control over the other cartel leaders.
=== NMR spectroscopy === Hydrogen and deuterium nuclei are grossly different in their magnetic properties. Thus it is possible to distinguish between them by NMR spectroscopy. Deuterons will not be observed in a 1H NMR spectrum and conversely, protons will not be observed in a 2H NMR spectrum. Where small signals are observed in a 1H NMR spectrum of a highly deuterated sample, these are referred to as residual signals. They can be used to calculate the level of deuteration in a molecule. Analogous signals are not observed in 2H NMR spectra because of the low sensitivity of this technique compared to the 1H analysis. Deuterons typically exhibit very similar chemical shifts to their analogous protons. Analysis via 13C NMR spectroscopy is also possible: the different spin values of hydrogen (1/2) and deuterium (1) gives rise to different splitting multiplicities. NMR spectroscopy can be used to determine site-specific deuteration of molecules. Another method uses HSQC spectra. Typically HSQC spectra are recorded at a series of timepoints while the hydrogen is exchanging with the deuterium. Since the HSQC experiment is specific for hydrogen, the signal will decay exponentially as the hydrogen exchanges. It is then possible to fit an exponential function to the data, and obtain the exchange constant. This method gives residue-specific information for all the residues in the protein simultaneously The major drawback is that it requires a prior assignment of the spectrum for the protein in question.
Sources: en.wikipedia.org
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.
Very few controlled human studies focus on the seven-residue sequence itself. Most clinical data concern the full-length protein in cardiac or ophthalmic settings. Conclusions drawn for one form should not be assumed to transfer to the other.
Detection normally relies on reversed-phase liquid chromatography paired with mass spectrometry. Chromatographic retention time establishes the expected elution window, and the mass spectrum confirms the molecular ion. Immunoassays exist but can cross-react with related peptides.
TB-500 is a synthetic heptapeptide corresponding to a fragment of thymosin beta-4. It is used in laboratory research and is not an approved drug.