If you have been reading about Ac-LKKTETQ 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 2025-10-09. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
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.
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.
| 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 |
Identity and purity are usually assessed by reversed-phase high-performance liquid chromatography together with mass spectrometry. The chromatogram provides a purity estimate as a percentage of total peak area, while the mass spectrum confirms that the observed mass matches the expected value. Amino acid analysis or tandem mass spectrometry sequencing can provide additional confirmation. Reported purity figures depend on the column, gradient, and detection wavelength, so values from different laboratories are not directly comparable without method details.
Lyophilised peptide is normally reconstituted with sterile water or a neutral buffer shortly before use. Because repeated freeze-thaw cycles can degrade the material, dividing a reconstituted solution into single-use aliquots is a common practice. Working solutions are usually kept cold and protected from light. The exact shelf life depends on concentration, buffer composition, and handling, so it is often determined empirically rather than assumed.
Peptide bonds are susceptible to hydrolysis under extreme pH and to enzymatic cleavage if proteases are present. Heat, oxidising agents, and prolonged exposure to light also contribute to loss of material. Aggregation can occur at high concentrations or in certain buffer systems, and it may not be visible to the eye. Storage at -20 C or below is typical for both powder and aliquoted solutions, and desiccation of the powder is preferred.
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.
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.
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.
The compound is most often distributed as a lyophilized powder, appearing white to off-white and forming a loose cake or fluffy solid. It is hygroscopic to some degree, so brief exposure to humid air can add water weight and complicate weighing. The peptide dissolves readily in water and in neutral aqueous buffers, and aqueous solubility is generally described as high, well above the concentrations used in typical assays. Some polar organic solvents are also usable, which matters when a concentrated stock is prepared before dilution into buffer.
Interest in the peptide grew during the 2000s and 2010s, when studies of tendon and ligament injuries in horses reported changes in lesion size after treatment. Those reports circulated widely outside the scientific literature and shaped much of the current online discussion. Subsequent reviews noted inconsistent study design, small groups, and a shortage of independent replication. Popular descriptions often blur the line between the fragment, the complete protein, and unrelated growth factors, which complicates comparisons across sources.
TB-500 is a synthetic peptide whose sequence corresponds to a short fragment near the N-terminus of thymosin beta-4, a small protein present in most mammalian cells. The fragment is commonly cited as containing the actin-binding region of the parent molecule, which is why it appears in laboratory work on cell migration and tissue repair. Suppliers distribute it as a lyophilised powder intended for research use. Its identity is defined by amino acid sequence and by the presence of an acetyl group on the N-terminal residue.
=== Chemical detection === NASA contracted with Intelligent Optical Systems (IOS) to develop moisture- and pH-sensitive sensors to warn of corrosive conditions in aircraft before damage occurs. This sensor changes color in response to contact with its target. After completing the work with NASA, IOS was tasked by the U.S. Department of Defense to further develop the sensors for detecting chemical warfare agents and potential threats, such as toxic industrial compounds and nerve agents. IOS has sold the chemically sensitive fiber optic cables to major automotive and aerospace companies, who are finding a variety of uses for the devices such as aiding experimentation with nontraditional power sources, and as an economical "alarm system" for detecting chemical release in large facilities.
=== Anti-DFS70 antibodies === Anti-DFS70 antibodies generate a dense fine speckled pattern in indirect immunofluorescence and are found in normals and in various conditions, but are not associated with a systemic autoimmune pathology. Therefore, they can be used to help to rule out such conditions in ANA positive individuals. A significant number of patients are diagnosed as systemic lupus erythematosus or undifferentiated connective tissue disease largely based on a positive ANA. In case no defined autoantibody can be detected (e.g. anti-ENA antibodies), the testing of anti-DFS70 antibodies is recommended to verify the diagnosis. Anti-DFS70 antibody tests are available as CE-marked tests. Until now, no FDA cleared assay is available.
The liver is a vital organ and supports almost every other organ in the body. Severe or end-stage liver failure has dire consequences for the body's overall health and quality of life. Visible signs of liver disease include jaundice and ascites. Hepatomegaly refers to an enlarged liver and may be caused by several underlying diseases. It can be palpated in an abdominal exam. Scarring (fibrosis) of the liver from any cause can lead to cirrhosis. Cirrhosis increases the resistance to blood flow in the liver, and can result in portal hypertension. Congested anastomoses between the portal venous system and the systemic circulation, can be a subsequent condition. The most common chronic liver disease is nonalcoholic fatty liver disease, which affects an estimated one-third of the world population. Hepatitis is a common condition of inflammation of the liver. The cause is usually viral, and the most common of these infections are hepatitis A, B, C, D, and E. Some of these infections are transmitted sexually or through non-sterile needles. Inflammation can also be caused by other viruses in the family Herpesviridae such as the herpes simplex virus. Chronic (rather than acute) infection with hepatitis B virus or hepatitis C virus is the main cause of liver cancer. Globally, about 248 million individuals are chronically infected with hepatitis B (with 843,724 in the U.S.), and 142 million are chronically infected with hepatitis C (with 2.7 million in the U.S.).
methyl Also carbinyl. The alkyl functional group derived from methane, consisting of one carbon atom bonded to three hydrogen atoms, with the chemical formula CH3. It is the simplest hydrocarbon and occurs as a substituent in numerous organic compounds, though it may also exist independently as an ion or radical. In IUPAC nomenclature, the presence of a methyl substituent is indicated with the prefix methyl in the name of the compound, or with the abbreviation Me in chemical formulae; e.g. methyl alcohol (methanol) is often written with the formula CH3OH or MeOH.
Throughout the 1850s, the sectional conflict regarding slavery was further inflamed by national legislation in the U.S. Congress and decisions of the Supreme Court. In Congress, the Fugitive Slave Act of 1850 mandated the forcible return to their enslavers in the South of persons taking refuge in non-slave states, while the Kansas–Nebraska Act of 1854 effectively gutted the anti-slavery requirements of the Missouri Compromise. In its Dred Scott decision of 1857, the Supreme Court ruled against an enslaved person brought into non-slave territory, simultaneously declaring the entire Missouri Compromise to be unconstitutional. These and other events exacerbated tensions between North and South that would culminate in the American Civil War (1861–1865). Beginning with South Carolina, 11 slave-state governments voted to secede from the United States in 1860–1861, joining to create the Confederate States of America. All other state governments remained loyal to the Union. War broke out in April 1861 after the Confederacy bombarded Fort Sumter. Following the Emancipation Proclamation on January 1, 1863, many freed slaves joined the Union army. The war began to turn in the Union's favor following the 1863 Siege of Vicksburg and Battle of Gettysburg, and the Confederates surrendered in 1865 after the Union's victory in the Battle of Appomattox Court House.
Sources: en.wikipedia.org
In June 2000, Labcorp acquired the laboratory testing business of Pathology Medical Laboratories. In May 2001, Labcorp acquired Path Lab Holdings, the largest regional laboratory in New England. In June 2001, it acquired ViroMed, which specialized on clinical diagnostic testing in virology, molecular biology, serology, microbiology, mycology and mycobacteriology, as well as in tissue and eye bank testing. In 2013, it closed the Viromed facility in Minnetonka, Minnesota and laid off 79 workers. In December 2001, Labcorp became the exclusive marketer for genomics and proteomics tests for breast cancer, colon cancer, melanoma, and hypertension made by Myriad Genetics. In March 2002, Roche sold its remaining interest in the company. In May 2002, Labcorp acquired Dynacare, a Canadian medical laboratory services company, for $480 million. In January 2003, Labcorp acquired Dianon, a provider of oncology and genomic diagnostic testing services, for $598 million in cash. In February 2005, the company acquired US Pathology Labs Inc., a provider of anatomical pathology and oncology testing services, for $155 million. In March 2005, Labcorp acquired Esoterix, a provider of specialty reference testing, for approximately $150 million in cash from Behrman Capital. In November 2006, Labcorp acquired Litholink, a kidney stone analysis laboratory. In January 2008, Labcorp acquired Tandem Labs, a contract research organization specializing in advanced mass spectrometry, immunoanalytical support, pharmacokinetics, and pharmacodynamics.
== Reaction mechanism == The reaction mechanism is not known in detail. Supposedly, the reaction begins with a nucleophilic attack of the amino group on the carbonyl carbon of the anhydride group of the N-carboxylic acid anhydride (1). After an intramolecular proton migration, a 1,4-proton shift and the cleavage of carbon dioxide follows, resulting in the peptide bond in the final product (2):
In 1955, Soviet paleontologist Evgeny Maleev named a new species, Tyrannosaurus bataar, from Mongolia. By 1965, this species was renamed as a distinct genus, Tarbosaurus bataar. While most paleontologists continue to maintain the two as distinct genera, some authors such as Thomas Holtz, Kenneth Carpenter, and Thomas Carr argue that the two species are similar enough to be considered members of the same genus, restoring the Mongolian taxon's original binomial name. Some specimens from the Late Cretaceous deposits of China have been described as new species of Tyrannosaurus: T. "lanpingensis" based on isolated lateral tooth from the red beds of Yunnan in 1975; T. "turpanensis" from the Subashi Formation, Turpan Basin, Xinjiang in 1978; and T. luanchuanensis from the Quiba Formation in Henan Province in 1979–1980. The former two taxa were published without detailed descriptions and are therefore nomina nuda. T. "turpanensis" and T. luanchuanensis were tentatively listed as junior synonyms of Tarbosaurus bataar by Holtz in 2004; Holtz also listed T. "lanpingensis," but as a nomen dubium. VGI, no. 231/3, a large phalanx bone, assigned to Tyrannosaurus sp. by Yarkov in 2000, was found in the Lower Maastrichtian of Bereslavka, Russia. In 2004, Averianov and Yarkov reinterpreted it as a metacarpal or metatarsal that possibly belongs to ceratosaur. In their 2023 overview, Averianov and Lopatin mention this specimen as well as a single tooth from the same site only as Theropoda indet.
=== Earliest recorded cases === OI has been identified in an ancient Egyptian infant mummified in around 1000 BC, originally dismissed by archaeologists as containing the remains of a monkey. The Norse king Ivar the Boneless, who lived c. 800 CE, is speculated to have had OI as well. Nicolas de Malebranche is often credited as being the first person to describe the physical characteristics of OI in his 1688 book The Search after Truth, in which he describes a man who has had his "bones broken in the places a murderer's would be" all his life. His confident description of the pathology of the disorder, however, which creates what he termed «enfants monstrueux» ("monstrous children"), is scientifically void—he wrote that it was due to the mother's antepartum viewership of a public execution by breaking wheel. The earliest modern scientific studies of OI began in 1788 by Olof Jakob Ekman, who described the condition, which he termed "osteomalacia congenital", in his doctoral thesis and mentioned cases of it going back to 1678, all in the same family, through three generations. Ekman's description of the condition mentioned dwarfism, bone fragility, and bowing of the long bones. In 1831, Edmund Axmann gave a detailed description of it in himself and his two brothers, being the first to mention blue sclerae as a characteristic sign of OI. Jean Lobstein first described the mild form of the condition, today known as type I, in 1833, calling it "osteopsathyrosis idiopathica".
== Production and function == Hydroxyproline is produced by hydroxylation of the amino acid proline by the enzyme prolyl 4-hydroxylase following protein synthesis (as a post-translational modification). The enzyme-catalyzed reaction takes place in the lumen of the endoplasmic reticulum. Although it is not directly incorporated into proteins, hydroxyproline comprises roughly 4% of all amino acids found in animal tissue, an amount greater than seven other amino acids that are translationally incorporated.
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.
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.