If you have been reading about counter-ion and want a single page that covers the useful parts, this is it: definitions, context, how it is studied, and the questions that come up repeatedly.
Last reviewed on 2026-04-07. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
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.
Lyophilized peptide arrives as a dry cake that should stay sealed until use. Reconstitution is generally performed with sterile water or a buffered solution, and the resulting liquid should be handled gently to limit mechanical stress. Repeated freeze-thaw cycles are widely described as harmful to short peptides, so dividing a reconstituted batch into single-use portions is a common practice. Laboratories also record the solvent, concentration, and date of preparation on the vial label to keep later measurements traceable.
Dry powder is commonly held at minus twenty degrees Celsius, with some suppliers recommending lower temperatures for long-term archival storage. Once dissolved, solutions are typically kept cold and protected from light, since aqueous peptide solutions can lose integrity through hydrolysis or oxidation over time. Stability data specific to this fragment are limited in the public literature, and much of the guidance comes from general peptide handling practice rather than from controlled degradation studies. Users therefore treat stated shelf lives as approximate rather than fixed.
| Property | Value | Notes |
|---|---|---|
| Molecular formula | C38H68N10O14 | Calculated for the acetylated heptapeptide |
| Molecular weight | ~889 Da | Monoisotopic mass approximately 889.0 Da |
| Amino acid sequence | Ac-LKKTETQ | N-terminal acetylated seven-residue peptide |
| Appearance | White to off-white powder | Typically supplied as a lyophilized solid |
| Solubility class | Water-soluble | Peptides of this size generally dissolve in aqueous media |
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.
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.
Identity and purity are checked with reversed-phase high-performance liquid chromatography, which separates the target sequence from truncated or deletion analogues, and with mass spectrometry, which confirms the expected molecular mass. Amino acid analysis and peptide mapping give orthogonal confirmation but are used less often outside specialist laboratories. Counter-ion content varies: material purified on trifluoroacetic acid gradients retains trifluoroacetate, and ion exchange can convert the salt form. Residual water and solvent are measured by Karl Fischer titration or thermogravimetric analysis, and any purity figure should be read together with the method used to obtain it.
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 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.
== Principle == The reason for the stability of DNA, RNA or protein could be attributed to the fact that the biological material binds to the matrix of the filter paper and the process of drying excludes water which is an important factor necessary for protease or nuclease to act. Binding of the biological material also binds several inhibitors which may interfere with various nucleic acid amplification methods.
== Medical uses == Somapacitan is indicated for replacement of endogenous growth hormone in adults with growth hormone deficiency (GHD). GHD is a condition when the body doesn't produce enough growth hormone on its own. Growth hormone regulates many functions in the body including accumulation of fat in the trunk or central area of the body that can be associated with serious medical issues.
The 1974 Carnation Revolution in Portugal, which over the next year replaced Portuguese support for Smith with an independent, Marxist–Leninist Mozambique on Rhodesia's eastern frontier, greatly swung the war's momentum in favour of the nationalists (particularly ZANU, which was allied with Mozambique's governing FRELIMO party), and caused the sanctions on Rhodesia to finally begin having a noticeable effect. Diplomatic isolation, the sanctions, guerrilla activities and pressure from South Africa to find a settlement led the Rhodesian government to hold talks with the various black Rhodesian factions. Abortive conferences were held at Victoria Falls (in 1975) and Geneva (1976). Despite ideological and tribal rifts, ZANU and ZAPU nominally united as the "Patriotic Front" (PF) in late 1976 in a successful attempt to augment overseas support for the black Rhodesian cause. By the mid-1970s, it was apparent that white minority rule could not continue forever. Even South Africa's prime minister John Vorster realized that white rule in a country where blacks outnumbered whites 22:1 was not a realistic option. Smith, who was decisively re-elected three times during the 1970s, eventually came to this conclusion as well. He announced his acceptance in principle of one man, one vote during Henry Kissinger's Anglo-American initiative in September 1976, and in March 1978 concluded the Internal Settlement with non-militant nationalist groups headed by Bishop Abel Muzorewa, the Reverend Ndabaningi Sithole and Chief Jeremiah Chirau.
Sources: en.wikipedia.org
9 September South Vietnamese officials reported that nearly 5,000 South Vietnamese civilians have been killed by PAVN/VC terror during 1969. Funeral services for Ho Chi Minh were held in Ba Đình Square, Hanoi attended by more than 250,000 mourners. Foreign dignitaries in attendance included Alexei Kosygin, Premier of the Soviet Union, Li Xiannian, Vice Premier of China, Gustáv Husák, General Secretary of the Communist Party of Czechoslovakia, Ignacy Loga-Sowiński, Deputy Premier of Poland, Ion Gheorghe Maurer, Prime Minister of Romania, Sihanouk and Souvanna Phouma.
=== Lysosomal storage disorders === Lysosomal storage disorders are not included in newborn screening programs with high frequency. As a group, they are heterogenous, with screening only being feasible for a small fraction of the approximately 40 identified disorders. The arguments for their inclusion in newborn screening programs center around the advantage of early treatment (when treatment is available), avoiding a diagnostic odyssey for families and providing information for family planning to couples who have an affected child. The arguments against including these disorders, as a group or individually center around the difficulties with reliably identifying individuals who will be affected with a severe form of the disorder, the relatively unproven nature of the treatment methods, and the high cost / high risk associated with some treatment options. New York State started a pilot study to screen for Krabbe disease in 2006, largely due to the efforts of Jim Kelly, whose son, Hunter, was affected with the disease. A pilot screening program for four lysosomal storage diseases (Gaucher disease, Pompe disease, Fabry disease and Niemann-Pick disease was undertaken using anonymised dried blood spots was completed in Austria in 2010. Their data showed an increased incidence from what was expected in the population, and also a number of late onset forms of disease, which are not typically the target for newborn screening programs.
Gavi's funding for this platform was conditional on the platform meeting vaccine coverage goals. As of the mid-2010s, few in Gavi were working on HSS, most of the former pro-HSS people had left, and some at Gavi dismissed HSS as PR to gain support from pro-HSS donors and counter criticisms that Gavi was harming healthcare systems. Such criticisms were generally not a topic that Gavi engaged with internally; the lack of internal engagement with the issue has been criticized. The disagreements were fairly intense; when Bill Gates came to visit Gavi headquarters, employees would hide the HSS-related posters so that he would not be reminded of this aspect of Gavi's work. Julian Lob-Levitt, who was Gavi's CEO between 2004 and 2010, was rumoured to have left over conflicts around his support for health system strengthening. Seth Berkley has been the CEO of Gavi since 2011, as of 2020. It has been argued that Gavi's HSS spending in the early 2010s went to selective, disease-specific interventions repackaged as HSS. Gavi's HSS support at this time tended to focus on immunisation strengthening support, especially the building of cold chains. Gavi measured HSS using vaccination coverage as the sole indicator. It set the reporting indicators which were required of recipients of its funding; countries were not allowed to use similar indicators they already collected; this has been criticized for conferring a heavy accounting burden and diverting attention from indigenous goals.
Sources: en.wikipedia.org
small temporal RNA (stRNA) A subclass of microRNAs, originally described in nematodes, which regulate the timing of developmental events by binding to complementary sequences in the 3' untranslated regions of messenger RNAs and inhibiting their translation. In contrast to siRNAs, which serve similar purposes, stRNAs bind to their target mRNAs after the initiation of translation and without affecting mRNA stability, which makes it possible for the target mRNAs to resume translation at a later time.
Carbon nanotubes are modelled in a similar manner as traditional composites in which a reinforcement phase is surrounded by a matrix phase. Idealized models such as cylindrical, hexagonal and square models are common. The size of the micromechanics model is a function of the studied mechanical properties. The concept of representative volume element (RVE) is used to determine the appropriate size and configuration of the computer model to replicate the actual behavior of the CNT-reinforced nanocomposite. Depending on the material property of interest (thermal, electrical, modulus, creep), one RVE might predict the property better than the alternatives. While the implementation of the ideal model is computationally efficient, they do not represent microstructural features observed in scanning electron microscopy of actual nanocomposites. To incorporate realistic modeling, computer models are also generated to incorporate variability such as waviness, orientation and agglomeration of multiwall or single-wall carbon nanotubes.
== L == L-amino-acid alpha-ligase - L-ornithine N5 monooxygenase - lambda - Lamprin - Laser capture microdissection - latarcin - leucine zipper - leukemia - leukotriene-B4 20-monooxygenase - library - licodione synthase - ligase - linear epitope - linkage - linker protein - linoleate diol synthase - lipofectin - lipopolysaccharide kinase (Kdo/WaaP) family - lipopolysaccharide-transporting ATPase - lithocholate 6beta-hydroxylase - locus - LOC100507195 - LOD score - Long intergenic non-protein coding rna 1157 - lymphocyte - lysine—tRNA(Pyl) ligase -
=== Criticism of USAID termination === Andrew Natsios, the administrator for USAID during the George W. Bush administration, told PBS that, "With all due respect, none of these people know anything about AID. What does Musk know about international development? Absolutely nothing. He has a bunch of young kids in their 20s. They don't know. They're techies. They don't know anything about international development. They don't know anything about the Global South. They don't know anything about these — the programs and policies of the agency. AID is the most pro-business and pro-market of all aid agencies in the world. I can tell you that categorically. I am a conservative Republican. I'm not a liberal. And I have served in repeated Republican administrations." Michael Sobolik, a China analyst at the conservative Hudson Institute think tank and a former aide to Senator Ted Cruz (R-Texas), has stated, "Sure, USAID was doing some highly questionable stuff that’s worthy of review. But don’t throw the baby out with the bathwater. Beijing is hoping we do exactly that."
Sources: en.wikipedia.org
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.
No. Thymosin beta-4 is a 43-amino-acid protein, while TB-500 represents only a short N-terminal segment. The two should not be treated as interchangeable in experimental design.
It is often called a thymosin beta-4 fragment, Tβ4 fragment, or Ac-LKKTETQ. The name TB-500 is mainly a commercial or catalog label rather than a formal chemical name.
Dry lyophilized powder is usually kept frozen, desiccated, and out of direct light. Sealed vials are not opened until needed, because moisture uptake can degrade short peptides. Longer archival storage is often done at lower temperatures than routine working stock.