acetylated peptide is one of those subjects where the details matter more than the headlines. This page pulls together the background, the mechanisms, and the practical points readers ask about most.
Updated 2026-07-24. Numbers and descriptions here follow the published literature rather than marketing 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.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Molecular class | Synthetic peptide | N-terminal fragment of thymosin beta-4 |
| Residue count | Seven | Sequence LKKTETQ |
| Approximate mass | 889 Da | Acetylated seven-residue peptide |
| Common synonyms | TB4 fragment, TB500 | Not identical to full-length TB4 |
| Reported activity | Actin binding | Observed mainly in cell-free systems |
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.
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.
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.
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.
Detection in biological matrices generally relies on liquid chromatography coupled with tandem mass spectrometry, because the peptide lacks a convenient ultraviolet chromophore beyond the amide backbone. Immunoassays have been described, but antibodies raised against the fragment can cross-react with the full-length protein or with unrelated peptides, so findings usually require confirmation by a second technique. Sample preparation typically involves protein precipitation followed by solid-phase extraction. Reported detection windows depend on dose, route, matrix, and instrument sensitivity.
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.
==== 500–599 ==== Water Supply and Sewerage Services (Customer Service Standards) (Amendment) Regulations 1993 (S.I. 1993/500) Local Government Finance Act 1992 (Community Charge Benefits) Saving Order 1993 (S.I. 1993/502) Bovine Animals (Identification, Marking and Breeding Records) (Amendment) Order 1993 (S.I. 1993/503) Prisoner Escorts Rules 1993 (S.I. 1993/515) Prison (Amendment) Rules 1993 (S.I. 1993/516) Common Agricultural Policy (Wine) Regulations 1993 (S.I. 1993/517) Social Security Benefits (Miscellaneous Amendments) Regulations 1993 (S.I. 1993/518) Occupational and Personal Pension Schemes (Miscellaneous Amendments) Regulations 1993 (S.I. 1993/519) Local Authorities (Capital Finance) (Amendment) Regulations 1993 (S.I. 1993/520) National Health Service (General Medical and Pharmaceutical Services) (Scotland) Amendment Regulations 1993 (S.I. 1993/521) National Health Service (Charges for Drugs and Appliances) (Scotland) Amendment Regulations 1993 (S.I. 1993/522) National Health Service (Dental Services) (Miscellaneous Amendments) (Scotland) Regulations 1993 (S.I. 1993/523) National Health Service (Optical Charges and Payments) (Scotland) Amendment Regulations 1993 (S.I. 1993/524) Education (Fees and Awards) (Scotland) Amendment Regulations 1993 (S.I. 1993/525) Council Tax (Dwellings) (Scotland) Regulations 1993 (S.I. 1993/526) Council Tax (Transitional Reduction Scheme) (Scotland) Amendment (No.2) Regulations 1993 (S.I. 1993/527) Legal Aid in Contempt of Court Proceedings (Scotland) Amendment Regulations 1993 (S.I.
== Chemistry == Several chemical factors affect the ionophore activity. The activity of an ionophore-metal complex depends on its geometric configuration and the coordinating sites and atoms which create coordination environment surrounding the metal center. This affects the selectivity and affinity towards a certain ion. Ionophores can be selective to a particular ion but may not be exclusive to it. Ionophores facilitate the transport of ions across biological membranes most commonly via passive transport, which is affected by lipophilicity of the ionophore molecule. The increase in lipophilicity of the ionophore-metal complex enhances its permeability through lipophilic membranes. The hydrophobicity and hydrophilicity of the complex also determines whether it will slow down or ease the transport of metal ions into cell compartments. The reduction potential of a metal complex influences its thermodynamic stability and affects its reactivity. The ability of an ionophore to transfer ions is also affected by the temperature.
=== Immunodeficiency === In individuals lacking functional HLA-DM molecules, improper antigen presentation occurs, resulting in unwanted immune responses or lack of a response when danger is present. This has been shown experimentally through mouse knockout models. There will be an increase of CLIP, instead of peptide, presentation on APC surfaces. This can result in autoimmunity, if a T cell receptors recognize CLIP as a harmful antigen. There could also be no protein presentation at all, resulting in a lack of immune response.
Sources: en.wikipedia.org
=== „Ayda, Bär und Hase“ (2017) === The children's book „Ayda, Bär und Hase“ [Ayda, Bear and Rabbit] revisits the father-daughter relationship motif from the Neil Young book. The father, called Bâbâ, resembles other protagonists in Kermani's books (and the author himself): he has Iranian parents, lives in Cologne, and is a fan of the soccer team 1. FC Cologne and of Neil Young. The focus, however, is now on his five-year-old daughter Ayda, who is ill at ease with her small stature and befriends a bear and a rabbit who can talk. The book’s central themes include multicultural tolerance, the insight “that you can be happy even if not everything is perfect,” and overcoming fears together.
== Implementation == In one of various embodiments of EWOD-based microfluidic biochips, investigated first by Cytonix in 1987 and subsequently commercialized by Advanced Liquid Logic, there are two parallel glass plates. The bottom plate contains a patterned array of individually controllable electrodes and the top plate is coated with a continuous grounding electrode. A dielectric insulator coated with a hydrophobic is added to the plates to decrease the wet-ability of the surface and to add capacitance between the droplet and the control electrode. The droplet containing biochemical samples and the filler medium, such as the silicone oil, a fluorinated oil, or air, are sandwiched between the plates and the droplets travel inside the filler medium. In order to move a droplet, a control voltage is applied to an electrode adjacent to the droplet, and at the same time, the electrode just under the droplet is deactivated. By varying the electric potential along a linear array of electrodes, electrowetting can be used to move droplets along this line of electrodes.
=== Early roots === Long before modern companies existed, economies still needed people and firms that could bridge distance, timing, and risk between producers and buyers. Economic historians describe the rise of merchants and other intermediaries as a recurring feature of market development, including in ancient trade and later market commerce.
Entertainment Weekly critic Owen Gleiberman wrote that DiCaprio did not look old enough to play the part, but praised him as "a fluid and instinctive actor, with the face of a mischievous angel". The Guardian's Alex von Tunzelmann was similarly impressed with the actor's performance but found his talent wasted in the film. DiCaprio won a Golden Raspberry Award for Worst Screen Couple for the dual roles in 1999. Following the release of Titanic, and The Man in the Iron Mask, DeCaprio chose to reduce his workload "to learn to hear [his] own voice in choosing the roles" that he wanted to pursue. He said in 2000: "I have no connection with me during that whole Titanic phenomenon and what my face became around the world [...] I'll never reach that state of popularity again, and I don't expect to [...] It's not something I'm going to try to achieve either." DiCaprio was next cast to star in an earlier version of American Psycho (2000) for a reported salary of $20 million; after disagreements with Oliver Stone on the film's direction, DiCaprio left the project, taking the lead role in The Beach instead. Adapted from Alex Garland's 1996 novel, the film saw him play a backpacking American tourist who ends up in a secret island commune in the Gulf of Thailand. Budgeted at $50 million, the film earned almost three times that at the box office, but was negatively reviewed by critics, and earned him a nomination for the Golden Raspberry Award for Worst Actor. Todd McCarthy of Variety thought DiCaprio gave a compelling performance but his character lacked defining qualities.
Sources: en.wikipedia.org
No. Thymosin beta-4 is a 43-residue protein, while TB-500 refers to a seven-residue fragment corresponding to its N-terminal region. The two names are often used loosely in commercial and community writing, which obscures the difference in size, sequence, and likely behavior.
The fragment contains an actin-binding motif, and cell-free experiments show that it can interact with monomeric actin. That observation is the basis for interest in cell migration and repair processes. Effects reported in animals are not established for humans.
Purity is usually stated by the supplier rather than fixed by a pharmacopoeial monograph, and typical listings report a percentage from reverse-phase HPLC. Independent verification is uncommon. Because no single accepted specification exists, comparisons between lots and between suppliers are difficult.
Divide it into single-use aliquots and hold them frozen at -20 °C or below, protected from light. Repeated thawing of one container is the main avoidable source of variability.