A practical reference on prohibited list: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
This page was last updated on 2026-06-26 and is reviewed periodically as new material appears.
Lyophilised material is stable for extended periods when kept dry and cold, and suppliers typically recommend storage well below freezing. Once dissolved, the peptide is handled at refrigeration temperatures and used within a short period, because peptide bonds and the acetylated terminus can be affected by repeated freeze-thaw cycles, proteases, or extreme pH. Bacteriostatic water and saline are both described as solvents, although preservatives can interfere with some analytical workflows. Reconstituted solutions are inspected for particulates before use.
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.
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.
The designation TB-500 circulates in laboratory and catalog contexts without a single agreed definition. Most product listings apply it to an N-terminally acetylated seven-residue fragment of thymosin beta-4, while other listings attach the same label to the full 43-residue protein. Because the term is commercial rather than systematic, two entries bearing identical names may describe different molecules. Any documentation should therefore state which sequence a given sample is claimed to contain.
| Property | Value | Notes |
|---|---|---|
| Analytical method | LC-MS/MS | Preferred confirmatory technique |
| Appearance | White to off-white powder | Lyophilised form |
| Solubility | Freely soluble in water | Also described in saline |
| Storage temperature | Below -20 °C for powder | Short-term refrigeration for solutions |
| Regulatory status | Prohibited in sport | Listed under peptide hormones |
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.
Lyophilised peptide powders are hygroscopic, and the fragment absorbs atmospheric moisture when a vial is opened at room temperature. Weighing and aliquoting are normally done quickly in a dry environment, and stock solutions are divided into single-use portions before freezing. Repeated freeze-thaw cycles are avoided because they promote aggregation and can shift the measured content of a vial. These practices are general to synthetic peptides rather than unique to this sequence, but they matter more for short chains kept for long periods.
The seven-residue chain carries several polar and charged side chains, so it dissolves readily in water and in aqueous buffers near neutral pH. No cysteine is present, so disulphide formation is not a concern and reducing agents are unnecessary. Dilute ammonium hydroxide or acetonitrile-water mixtures are sometimes used for stock solutions when initial dissolution is slow. Strongly alkaline conditions and prolonged contact with oxidising agents are avoided because they can modify lysine-containing stretches, and haze in solution usually signals incomplete dissolution or aggregated material.
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.
Discussion of TB-500 appears in several distinct literatures that rarely cite one another. Peer-reviewed studies usually describe in vitro assays or small animal experiments and are cautious about extrapolation. Veterinary and sports communities circulate anecdotal reports with limited methodological detail. Commercial listings add a third layer, often using the name interchangeably with thymosin beta-4 even though the two molecules differ in size and sequence. Regulatory status varies by country, and the compound is not a licensed medicine in most jurisdictions, so readers comparing sources should check which molecule and which purity each source actually describes.
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.
=== Structural drawings === Organic molecules are described more commonly by drawings or structural formulas, combinations of drawings and chemical symbols. The line-angle formula is simple and unambiguous. In this system, the endpoints and intersections of each line represent one carbon, and hydrogen atoms can either be notated explicitly or assumed to be present as implied by tetravalent carbon.
Protein–protein interactions regulate enzymatic activity, control progression through the cell cycle, and allow the assembly of large protein complexes that carry out many closely related reactions with a common biological function. Proteins can bind to, or be integrated into, cell membranes. The ability of binding partners to induce conformational changes in proteins allows the construction of enormously complex signaling networks. As interactions between proteins are reversible and depend heavily on the availability of different groups of partner proteins to form aggregates that are capable to carry out discrete sets of function, study of the interactions between specific proteins is a key to understand important aspects of cellular function, and ultimately the properties that distinguish particular cell types.
As for Thrombotic disease, there have been several attempts to identify the contribution of α2β1-related genes to the development of this disorder. For example, polymorphisms in the ITGA2 gene can influence the density of α2β1 receptors in the platelet membrane, thus affecting the interaction of platelets with collagen and, consequently, their ability to form thrombi. However, the relationship of the described polymorphisms to myocardial infarction or ischemic stroke was rather inconsistent. It has also been reported that ITGA2 can be used as a biomarker for the diagnosis and prognosis of diseases. Overexpression of the ITGA2 gene is correlated with worse outcomes of several types of cancers, which implies the possibility of predicting aggressiveness, metastasis and survival based on the expression of this protein. With further development of transcriptomics and proteomics studies, ITGA2 was recognized as one of the candidates for a biomarker of disease progression and evaluation of the effect of targeted therapies. Since this integrin is responsible for many pathologies, it has become an attractive target for therapy. Monoclonal antibodies, peptides, and other molecules were developed to inhibit the functions of integrin α2β1 related to binding of cells to extracellular matrix components and subsequent signal transduction. However, there are no specific therapeutic agents targeting integrin α2β1 currently available for clinical use.
Nobelium (102No) is a synthetic element, and thus a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotope to be synthesized (and correctly identified) was 254No in 1966. There are fourteen known radioisotopes, which are 248No to 260No and 262No, and many isomers. The longest-lived isotope is 259No with a half-life of 58 minutes. The longest-lived isomer is 251m1No with a half-life of 1.02 seconds.
== Sources == Barceloux, Donald G., ed. (2008). Medical toxicology of natural substances: foods, fungi, medicinal herbs, plants, and venomous animals. John Wiley & Sons. ISBN 978-0-471-72761-3. Furman, Jon (2007). Timber rattlesnakes in Vermont and New York: biology, history, and the fate of an endangered species. UPNE. ISBN 978-1-58465-656-2. Klauber, Laurence M. & Greene, Harry W. (1997). Rattlesnakes: their habits, life histories, and influence on mankind. University of California Press. ISBN 978-0-520-21056-1. Rubio, Manny (1998). Rattlesnake: Portrait of a Predator. Smithsonian Books. ISBN 1-56098-808-8.
Sources: en.wikipedia.org
== Further reading == Tai CH, Lee NC, Chien YH, Byrne BJ, Muramatsu SI, Tseng SH, et al. (February 2022). "Long-term efficacy and safety of eladocagene exuparvovec in patients with AADC deficiency". Molecular Therapy. 30 (2): 509–518. doi:10.1016/j.ymthe.2021.11.005. PMC 8822132. PMID 34763085.{{cite journal}}: CS1 maint: overridden setting (link)
On October 17, faced with the PAVN's demonstrated ability to fight a conventional battle, the French command decided to abandon Lạng Sơn before it could come under attack, leaving behind considerable amounts of military supplies. The Viet-Minh now controlled most of the northern half of Tonkin.
Ligation is the joining of two nucleotides, or two nucleic acid fragments, into a single polymeric chain through the action of an enzyme known as a ligase. The reaction involves the formation of a phosphodiester bond between the 3'-hydroxyl terminus of one nucleotide and the 5'-phosphoryl terminus of another nucleotide, which results in the two nucleotides being linked consecutively on a single strand. Ligation works in fundamentally the same way for both DNA and RNA. A cofactor is generally involved in the reaction, usually ATP or NAD+. Eukaryotic ligases belong to the ATP type, while the NAD+ type are found in bacteria (e.g. E. coli). Ligation occurs naturally as part of numerous cellular processes, including DNA replication, transcription, splicing, and recombination, and is also an essential laboratory procedure in molecular cloning, whereby DNA fragments are joined to create recombinant DNA molecules (such as when a foreign DNA fragment is inserted into a plasmid). The discovery of DNA ligase dates back to 1967 and was an important event in the field of molecular biology. Ligation in the laboratory is normally performed using T4 DNA ligase. It is broadly used in vitro due to its capability of joining sticky-ended fragments as well as blunt-ended fragments. However, procedures for ligation without the use of standard DNA ligase are also popular. Human DNA ligase abnormalities have been linked to pathological disorders characterized by immunodeficiency, radiation sensitivity, and developmental problems.
The minerals, results of biomineralization processes regulated by the environment or bacteria, are also essential components of the exopolysaccharides. They provide structural integrity to biofilm matrix and act as a scaffold to protect bacterial cells from shear forces and antimicrobial chemicals. The minerals in EPS were found to contribute to morphogenesis of bacteria and the structural integrity of the matrix. For example, in Bacillus subtilis, Mycobacterium smegmatis, and Pseudomonas aeruginosa biofilms, calcite (CaCO3) contributes to the integrity of the matrix. The minerals also associate with medical conditions. In the biofilms of Proteus mirabilis, Proteus vulgaris, and Providencia rettgeri, the minerals calcium and magnesium cause catheter encrustation.
Sources: en.wikipedia.org
The most common approach is liquid chromatography with tandem mass spectrometry after extraction from blood or urine. Immunoassays exist but are generally treated as screening tools because of cross-reactivity.
Dry lyophilised powder is normally kept frozen and protected from moisture and light. Dissolved material is handled cold and used promptly to limit degradation.
It is not licensed as a medicine in major markets and is distributed as a research chemical. Sports organisations prohibit its use, and some countries restrict import and supply.
Usually not, though usage overlaps. The label most often refers to a short acetylated fragment of the parent protein, while thymosin beta-4 itself is the full 43-residue molecule. Because suppliers vary, a sequence statement is needed to settle the question for any particular lot.