This is a working overview of TB-500, written for readers who want more than a one-paragraph summary but less than a textbook.
Reviewed 2026-05-31. Anything still debated is marked as such rather than presented as settled.
Lyophilized peptide powder is normally held desiccated at −20 °C, with −80 °C used for longer storage periods. Allowing a sealed vial to reach room temperature before opening is standard practice, because condensation forming on cold powder introduces moisture. Once dissolved, solutions are typically kept cold and shielded from light. Repeated freeze-thaw cycles are avoided because they encourage aggregation and gradual loss of material. These conventions are general to synthetic peptides rather than unique to any one sequence.
Purity and identity are separate measurements and are often confused. Reverse-phase high-performance liquid chromatography, usually with ultraviolet detection near 214 nanometres, reports the share of total peak area belonging to the target compound. Mass spectrometry by electrospray or matrix-assisted laser desorption then checks whether the observed mass matches the expected sequence. Neither measurement alone shows that a vial holds the intended peptide. Peptide content, meaning the fraction of vial mass that is genuine peptide rather than counter-ion, water or residual acid, is reported separately and is frequently lower than the stated purity figure.
The regulatory position is broadly consistent across major jurisdictions: no thymosin beta-4 fragment is an approved medicine, and laboratory material is commonly labelled as not intended for human consumption. Anti-doping rules in sport list thymosin beta-4 and its fragments among prohibited peptide hormones. Because these products travel through research-chemical channels rather than pharmaceutical supply chains, quality varies considerably between vendors. Independent testing of identity, purity and sterility is the only dependable check, and a certificate of analysis describes one batch rather than a supplier's whole catalogue.
TB-500 is a short synthetic peptide sold under a trade name rather than a systematic chemical name. Suppliers usually describe it as a fragment of thymosin beta-4 and ship it as a lyophilised powder intended for laboratory use. Because the label is commercial, the exact sequence attributed to it is not fully consistent across catalogues, and some listings present a seven-residue peptide while others describe related fragments of similar length. It is not an approved medicine in any major jurisdiction, and it is handled as a research chemical.
Thymosin beta-4 itself is a natural peptide of 43 residues found in many cell types and body fluids. Its best-characterised function is binding and sequestering actin monomers, which influences cytoskeletal dynamics. The sequence most often associated with TB-500, LKKTETQ, corresponds to part of that actin-binding region. A different fragment, Ac-SDKP, is also derived from the same parent peptide and is studied in its own right, which is one reason discussions of thymosin fragments can become confusing. The two are structurally distinct and are not interchangeable.
Interest in the fragment grew during the 1990s and 2000s, when it moved from laboratory work into sports and supplement markets. Anti-doping bodies added thymosin beta-4 fragments to prohibited lists, and a small number of adverse analytical findings have been reported in competition testing. Published controlled human trials remain scarce. Most mechanistic evidence comes from cell culture and animal models, and those studies examine endpoints such as cell migration, wound closure and inflammation markers. That evidence supports research interest but does not establish clinical benefit, and broad regenerative claims should be read as unverified.
| Property | Value | Notes |
|---|---|---|
| Dosage form | Lyophilized powder in sealed vial | Reconstituted before analytical or laboratory use |
| Reconstitution solvent | Sterile or bacteriostatic water | Bacteriostatic water limits microbial growth in multi-use vials |
| Typical working pH | Near neutral, buffered | Strongly acidic or basic conditions promote degradation |
| Stability indicator | Loss of main HPLC peak over time | Aggregation and oxidation are common degradation routes |
| Documentation | Batch certificate of analysis | Covers identity, purity and sometimes sterility testing |
Material is normally supplied as a lyophilised powder in a sealed vial. The powder is hygroscopic, so exposure to humid air leads to water uptake, caking and gradual loss of the fluffy texture that indicates a good freeze-dry. Vials are best kept sealed with desiccant, protected from light and stored cold. Letting a cold vial warm to room temperature before opening reduces condensation on the contents. Purity is normally reported from a chromatographic run, and that figure applies to the batch as tested rather than to the vial after repeated opening.
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.
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.
Regulatory status differs by country, but TB-500 is not an approved pharmaceutical in major jurisdictions. It is commonly sold as a research chemical for laboratory use, which places responsibility for identity and purity on the supplier and the laboratory. Published human data are limited, and most reports involve preclinical models or cell culture. Questions about whether the fragment mimics all actions of thymosin beta-4, and under which conditions, remain open. Independent verification of any material is therefore a practical requirement in research settings.
=== Neutrinos === The study of beta decay provided the first physical evidence for the existence of the neutrino. In both alpha and gamma decay, the resulting alpha or gamma particle has a narrow energy distribution, since the particle carries the energy from the difference between the initial and final nuclear states. However, the kinetic energy distribution, or spectrum, of beta particles measured by Lise Meitner and Otto Hahn in 1911 and by Jean Danysz in 1913 showed multiple lines on a diffuse background. These measurements offered the first hint that beta particles have a continuous spectrum. In 1914, James Chadwick used a magnetic spectrometer with one of Hans Geiger's new counters to make more accurate measurements which showed that the spectrum was continuous. The results, which appeared to be in contradiction to the law of conservation of energy, were validated by means of calorimetric measurements in 1929 by Lise Meitner and Wilhelm Orthmann. If beta decay were simply electron emission as assumed at the time, then the energy of the emitted electron should have a particular, well-defined value. For beta decay, however, the observed electrons had a broad distribution of energies. A second problem is related to the conservation of angular momentum. Molecular band spectra showed that the nuclear spin of nitrogen-14 is 1 (i.e., equal to the reduced Planck constant) and more generally that the spin is integral for nuclei of even mass number and half-integral for nuclei of odd mass number. This was later explained by the proton-neutron model of the nucleus.
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== Occurrence == Together with norvaline, norleucine is found in small amounts in some bacterial strains where its concentration can approach millimolar. Its biosynthesis has been examined. It arises via the action of 2-isopropylmalate synthase on α-ketobutyrate. The incorporation of Nle into peptides reflects the imperfect selectivity of the associated aminoacyl-tRNA synthetase. In Miller–Urey experiments probing prebiotic synthesis of amino acids, norleucine and especially norvaline are formed.
Sources: en.wikipedia.org
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== Medical use == Lixisenatide is used as adjunct to diet and exercise to treat type 2 diabetes. In the European Union, its use is limited to complementing insulin therapy. As of 2017 it is unclear if they affect a person's risk of death. It is provided in an autoinjector containing fourteen doses and is injected subcutaneously. Lixisenatide should not be used for people who have problems with stomach emptying. Lixisenatide delays emptying of the stomach, which may change how quickly other drugs that are taken by mouth take effect.
== In fiction == The creation of a mirror-image human is the basis of the 1950 short story "Technical Error" by Arthur C. Clarke. In this story, a physical accident transforms a person into his mirror image, speculatively explained by travel through a fourth physical dimension. H. G. Wells' The Plattner Story (1896) is based on a similar idea. In the 1970 Star Trek novel Spock Must Die! by James Blish, the science officer of the USS Enterprise is replicated in mirror-image form by a transporter mishap. He locks himself in the sick bay where he is able to synthesize mirror-image forms of basic nutrients needed for his survival. An alien machine that reverses chirality, and a blood-symbiont that functions properly only when in one chirality, were central to Roger Zelazny's 1976 novel Doorways in the Sand. On the titular planet of Sheri S. Tepper's 1989 novel Grass, some lifeforms have evolved to use the right-handed isomer of alanine. In the Mass Effect series, chirality of amino acids in foodstuffs is discussed often in both dialogue and encyclopedia files. In the 2014 science fiction novel Cibola Burn by James S. A. Corey, the planet Ilus has indigenous life with partially-mirrored chirality. This renders human colonists unable to digest native flora and fauna, and greatly complicates conventional farming. Consequently, the colonists have to rely upon hydroponic farming and food importation. In the 2017 Daniel Suarez novel Change Agent, an antagonist, Otto, nicknamed the "Mirror Man", is revealed to be a genetically engineered mirror-image human.
Sources: en.wikipedia.org
Desiccated storage at −20 °C is conventional, with −80 °C for extended periods. Vials should be warmed to room temperature before opening to prevent condensation on the powder.
It usually reports batch-specific results for purity by chromatography, identity by mass spectrometry, and sometimes peptide content and residual solvents. It applies only to the batch tested, not to a supplier's wider stock.
Purity describes the proportion of the chromatographic signal from the target compound, while peptide content measures how much of the vial's physical mass is peptide. Counter-ions, water and residual acid make up the remainder, so content values are commonly lower.
No. Thymosin beta-4 is a 43-residue natural peptide, while TB-500 is a commercial label applied to a short synthetic fragment of it. The two differ in length, sequence coverage and how they are handled in the laboratory.