A practical reference on thymosin beta-4 fragment: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
This page was last updated on 2025-11-05 and is reviewed periodically as new material appears.
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.
The compound circulates in the literature as a research reagent rather than an approved therapeutic. Regulatory agencies in several countries have not authorized it for medical use, and sporting bodies list related thymosin beta-4 peptides among prohibited substances. Suppliers typically market it with a purity figure and a certificate of analysis, while peer-reviewed clinical reports remain sparse. Discussions therefore often separate laboratory findings from anecdotal reports, and reviewers tend to note the small size and methodological limits of the available studies.
TB-500 refers to a synthetic peptide fragment derived from the actin-binding region of thymosin beta-4, a protein present in most mammalian cells. The full protein contains forty-three amino acids, while the commonly sold fragment is a much shorter acetylated sequence, often cited as LKKTETQ. The fragment retains part of the actin-binding motif but lacks the remainder of the parent protein. Material sold under this name is usually lyophilized powder intended for laboratory research, and it is not a finished pharmaceutical product.
| 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 |
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.
TB-500 is a synthetic seven-residue peptide whose sequence, LKKTETQ, matches the N-terminal actin-binding region of thymosin beta-4. It is usually supplied in an N-terminally acetylated form, a modification that blocks the free amino terminus and can influence behavior in solution. In the research literature the same sequence appears under several names, including thymosin beta-4 fragment and shortened thymosin beta-4. Because it is a short peptide rather than the full 43-residue parent protein, its measured properties differ from those reported for thymosin beta-4 as a whole, and the two are not interchangeable in experimental design.
Thymosin beta-4 itself is a small, widely expressed protein that sequesters monomeric actin and participates in cell migration, angiogenesis, and tissue repair. Researchers have examined the shortened fragment as a possible mimic of some of these activities, reasoning that the actin-binding motif lies within the first few residues. Binding to monomeric actin has been observed in cell-free systems. Whether the fragment reproduces the broader effects of the full protein in living tissue remains an open question, and findings from animal models are frequently cited without a clear bridge to human physiology.
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.
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.
=== Drug development === ITC can provide insights into drug development by charactering the affinity, selectivity, ligand-induced conformational changes, and drug partitioning into membranes. Binding affinity carries a huge importance in medicinal chemistry, as drugs need to bind to the protein effectively within a desired range. An exothermic binding process with a favorable enthalpy is considered a desirable characteristic for specific protein binders, as it indicates strong potential for optimization and high selectivity. However, determining enthalpy changes and optimization of thermodynamic parameters are hugely difficult when designing drugs. ITC troubleshoots this issue easily by deducing the binding affinity, enthalpic/entropic contributions and its binding stoichiometry.
However the combined treatment may include serious side effects so is presently only recommended when rituximab has not worked alone. Finally, plasmapheresis, which involves filtering blood to remove antibodies, may be useful in acute hemolytic crisis and before surgery requiring hypothermia, however its effect is only short term. Removing the spleen is not recommended for cold agglutinin disease. In addition, because severe cold agglutinin disease requires very high doses of corticosteroids (levels not considered safe), corticosteroid treatment is no longer a recommended treatment in severe cases. Several possible therapies have been reported in a few case reports to have successfully treated people who are not responding to the treatments listed above. However more studies need to be performed before the safety and effectiveness of these therapies can be determined. Sutimlimab (Enjaymo) was approved for medical use in the United States in February 2022.
=== Other === AMH production by the Sertoli cells of the testes remains high throughout childhood in males but declines to low levels during puberty and adult life. AMH has been shown to regulate production of sex hormones, and changing AMH levels (rising in females, falling in males) may be involved in the onset of puberty in both sexes. Functional AMH receptors have also been found to be expressed in neurons in the brains of embryonic mice, and are thought to play a role in sexually dimorphic brain development and consequent development of gender-specific behaviours. In a clade of Sebastes rockfishes in the Northwest Pacific Ocean, a duplicated copy of the AMH gene (called AMHY) is the master sex-determining gene. In vitro experiments demonstrate that the overexpression of AMHY causes female-to-male sex reversal in at least one species, S. schlegelii.
=== Vedolizumab === Vedolizumab is very similar to natalizumab in that it is a humanized IgG monoclonal antibody, but vedolizumab is an IgG1 that specifically blocks the alpha 4 beta 7 integrin that is located primarily on cells in the gastrointestinal tract. It is promoted as being gut specific due to the localization of alpha 4 beta 7 integrin in the gastrointestinal tract and was the first biologic to be made specifically for inflammatory bowel disease.
=== General characteristics of the active substance === Salmon calcitonin is rapidly absorbed and eliminated. Peak plasma concentrations are attained within the first hour of administration. Animal studies have shown that calcitonin is primarily metabolised via proteolysis in the kidney following parenteral administration. The metabolites lack the specific biological activity of calcitonin. Bioavailability following subcutaneous and intramuscular injection in humans is high and similar for the two routes of administration (71% and 66%, respectively). Calcitonin has short absorption and elimination half-lives of 10–15 minutes and 50–80 minutes, respectively. Salmon calcitonin is primarily and almost exclusively degraded in the kidneys, forming pharmacologically inactive fragments of the molecule. Therefore, the metabolic clearance is much lower in patients with end-stage kidney failure than in healthy subjects. However, the clinical relevance of this finding is not known. Plasma protein binding is 30% to 40%.
Sources: en.wikipedia.org
== Legal status == The US Drug Enforcement Administration issued a notice of intent to publish a temporary order to schedule isotonitazene in Schedule I of the Controlled Substances Act, which came into effect on 20 August 2020.
=== Paleomagnetic dating === A sequence of paleomagnetic poles (usually called virtual geomagnetic poles), which are already well defined in age, constitutes an apparent polar wander path (APWP). Such a path is constructed for a large continental block. APWPs for different continents can be used as a reference for newly obtained poles for the rocks with unknown age. For paleomagnetic dating, it is suggested to use the APWP in order to date a pole obtained from rocks or sediments of unknown age by linking the paleopole to the nearest point on the APWP. Two methods of paleomagnetic dating have been suggested: (1) the angular method and (2) the rotation method. The first method is used for paleomagnetic dating of rocks inside of the same continental block. The second method is used for the folded areas where tectonic rotations are possible.
Synovial cavity: all diarthroses have the characteristic space between the bones that is filled with synovial fluid. Joint capsule: the fibrous capsule, continuous with the periosteum of articulating bones, surrounds the diarthrosis and unites the articulating bones; the joint capsule consists of two layers - (1) the outer fibrous membrane that may contain ligaments and (2) the inner synovial membrane that secretes the lubricating, shock absorbing, and joint-nourishing synovial fluid; the joint capsule is highly innervated, but without blood and lymph vessels, and receives nutrition from the surrounding blood supply via either diffusion (slow), or via convection (fast, more efficient), induced through exercise. Articular cartilage: the bones of a synovial joint are covered by a layer of hyaline cartilage that lines the epiphyses of the joint end of the bone with a smooth, slippery surface that prevents adhesion; articular cartilage functions to absorb shock and reduce friction during movement. Many, but not all, synovial joints also contain additional structures:
== Chromosome and gene abnormalities == Most cases of MFS have tumor cells that contain complex chromosome and/or gene abnormalities including ring chromosomes (i.e. chromosome whose ends are fused together to form a ring), double minutes (i.e. small fragments of extrachromosomal DNA), chromosomes with deletions of part of their genetic material, and chromosome translocations (i.e. abnormal switches in genetic material between different chromosomes). There were no apparent differences in these abnormalities between lower grade and higher grade tumors but their numbers were higher and more prevalent in recurrent tumors. These forms of chromosome/gene cytogenetic alterations are commonly found in various tumor types regardless of their grade or severity. Tumor cell mutations or deletions in the NF1 gene occur ~10% of MFS cases while mutations in the CDKN2A/CDKN2B and amplifications in the CDK6, CCND1, and MDM2 genes occur in rare MFS cases. While the cells in many tumor types express specific chromosome/gene abnormalities that help in determining their diagnoses, the cited chromosome and gene abnormalities discovered in TBS tumor cells have not yet been found specific enough to be of help in diagnosing MFS. The chromosome/gene abnormalities have not yet been defined in the epithelioid variant of MFS.
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.
TB-500 is a name used for a short synthetic peptide fragment taken from the actin-binding region of thymosin beta-4. Material sold under this label is usually a lyophilized powder supplied for laboratory research rather than a licensed medicine. The commonly cited sequence is LKKTETQ.