Ac-LKKTETQ 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 2026-07-10. Numbers and descriptions here follow the published literature rather than marketing material.
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.
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.
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.
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.
| 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 |
Controlled human trials of the short fragment are scarce. Much of what appears in review articles is extrapolated from animal models or from studies of the parent protein, and literature searches return a larger body of cardiac and ophthalmic work on thymosin beta-4 than on the abbreviated peptide. Regulatory treatment differs by jurisdiction, and in several countries the material is handled as a research chemical rather than an approved therapeutic. Statements about human benefit should be read as provisional.
Biological interest in this peptide centers on its relationship to actin dynamics. Thymosin beta-4 binds monomeric actin through an LKKTET motif, and a short sequence carrying that motif can compete with other actin-binding proteins in cell-free preparations. Investigators propose that such competition shifts the balance between filament assembly and disassembly, which in turn affects how readily a cell extends protrusions and migrates. Most of the supporting observations come from cultured cells and purified protein systems rather than from intact organisms.
Animal work has examined the peptide in models of cardiac injury, skin wounding, and corneal repair, with reported outcomes covering cell migration, inflammatory cell influx, and tissue remodeling. Several of those experiments used the full-length protein or longer fragments instead of the seven-residue sequence, which makes direct comparison between reports difficult. Results are generally described as tissue-dependent, and effect sizes vary considerably across laboratories. Independent replication is uneven, so the overall picture is incomplete rather than settled.
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.
TB-500 is a research peptide whose sequence matches residues 17 to 23 of thymosin beta-4, a 43-residue protein present in most mammalian cells. The chain is seven amino acids long, written as LKKTETQ, and is normally supplied with an acetyl group on the N-terminus. Suppliers list it as a lyophilised powder under the code name TB-500, and the same sequence appears elsewhere in catalogues as the thymosin beta-4 actin-binding fragment. The label is commercial rather than systematic, so no single authority fixes exactly what TB-500 denotes.
Thymosin beta-4 was isolated from calf thymus in the early 1980s and later characterised as an abundant intracellular actin-sequestering protein. Interest in short synthetic fragments grew once the actin-binding motif had been mapped to the middle of the sequence. TB-500 came out of that line of work as a truncated analogue rather than a natural isolate, and it is now sold mainly to laboratories. Published studies on the fragment have been largely in vitro or in animal models, and controlled human trials remain sparse, so claims about effects in people rest on extrapolation.
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.
==== Authority to canonize ==== For several centuries, the bishops, or in some places only the primates and patriarchs, could grant martyrs and confessors public ecclesiastical honour; such honour, however, was always decreed only for the local territory of which the grantors had jurisdiction. Universal acceptance of the cultus was said to be made possible by the pope because he claimed to be the sole ruler the universal Catholic Church. Toward the end of the eleventh century the popes judged it necessary to restrict episcopal authority in this regard, and therefore decreed that the virtues and miracles of persons proposed for public veneration should be examined in councils, more specifically in general councils. Popes Urban II, Calixtus II, and Eugene III conformed to this discipline. It happened, even after these decrees, that "some, following the ways of the pagans and deceived by the fraud of the evil one, venerated as a saint a man who had been killed while intoxicated." Pope Alexander III (1159–81) prohibited his veneration in these words: "For the future you will not presume to pay him reverence, as, even though miracles were worked through him, it would not allow you to revere him as a saint unless with the authority of the Roman Church." Theologians disagree as to the full import of this decretal: either a new law was instituted, in which case the Pope then for the first time reserved the right of beatification to himself, or an existing law was confirmed.
== Clinical significance == Melanoma - Cancer affecting melanocytes Melanocytic tumors Melanocytic tumors of uncertain malignant potential Vitiligo - Decreased number of melanocytes due to autoimmune destruction causing decreased melanin Albinism - Normal number of melanocytes, but decreased melanin production due to decreased tyrosinase activity or defective tyrosine transport Melasma (Chloasma) - Patchy hyperpigmentation of the skin Normal number of melanocytes with increased melanin production causing hyperpigmentation. Associated with pregnancy or oral contraceptive pill use. Addison disease Nevus depigmentosus
Rhodesian politicians frequently reminded officials in the other two nations of common security interests based on the similarity of their restive internal situations. They saw strong parallels between their nation's position of being threatened by black nationalist insurgencies and the Portuguese predicament with FRELIMO in Mozambique, as well as to a lesser extent the insurgencies in South Africa and South West Africa. Under the auspices of the Alcora Exercise, the three countries' bureaucracies began routinely sharing information and seeking common diplomatic positions. Lieutenant General Alan Fraser, a senior strategist in the South African Defence Force wrote in 1970, "there can be no doubt in any of our minds that we have a common enemy: we, i.e. Portugal, the RSA and Rhodesia. Unless we are to lay ourselves open to the possibility of defeat in detail, we must fight this enemy jointly—if not simultaneously." Nevertheless, aside from intelligence-sharing and some limited coordination on the operational level in Mozambique, the Portuguese could offer Rhodesia little decisive assistance. Portuguese colonial administrators in Mozambique were preoccupied with FRELIMO and somewhat depleted by a decade of war, and little could be spared to assist a foreign ally. Rhodesia expected far more from South Africa, which possessed greater military resources and diplomatic influence abroad at the time. After the Carnation Revolution and the end of Portuguese rule in Mozambique in 1975, it was no longer viable for the Smith regime to sustain white minority rule indefinitely.
== Discovery == Adiponectin was first characterised in 1995 in differentiating 3T3-L1 adipocytes (Scherer PE et al.). In 1996 it was characterised in mice as the mRNA transcript most highly expressed in adipocytes. In 2007, adiponectin was identified as a transcript highly expressed in preadipocytes (precursors of fat cells) differentiating into adipocytes. The human homologue was identified as the most abundant transcript in adipose tissue. Contrary to expectations, despite being produced in adipose tissue, adiponectin was found to be decreased in obesity. This downregulation has not been fully explained. The gene was localised to chromosome 3q27, a region highlighted as affecting genetic susceptibility to type 2 diabetes and obesity. Supplementation by differing forms of adiponectin was able to improve insulin control, blood glucose and triglyceride levels in mouse models. The gene was investigated for variants that predispose to type 2 diabetes. Several single nucleotide polymorphisms in the coding region and surrounding sequence were identified from several different populations, with varying prevalences, degrees of association and strength of effect on type 2 diabetes. Berberine, an isoquinoline alkaloid, has been shown to increase adiponectin expression, which partly explains its beneficial effects on metabolic disturbances. Mice fed the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have shown increased plasma adiponectin. Curcumin, capsaicin, gingerol, and catechins have also been found to increase adiponectin expression.
Sources: en.wikipedia.org
=== General topics === Biological engineering Biomolecular engineering Chemical engineering Chemistry Electrical engineering Materials science and engineering Mechanical engineering Molecular design software Molecular electronics Molecular modeling Molecular nanotechnology Nanotechnology
== Processing == The first commercial process by which opiates are extracted from poppy straw was invented in Hungary by János Kabay. This process, known as the "poppy straw method", remains in use today. Kabay applied his new process initially to fields of opium poppies between the stages of flowering and maturity, while the fruits were green. This had several disadvantages: the immature poppy seeds could not be winnowed, so not only was the seed crop lost but their poppyseed oil interfered with the process; the abundant chlorophyll in the green plants also interfered; and an entire year's crop had to be processed in two months, as it reached the fruit stage. Kabay soon found that the process could be applied to poppy straw residue from the poppy seed harvest, thereby eliminating all these disadvantages. Poppy straw is first pulverized, then washed as many as six to ten or more times in water which may have an acid added to increase solubility, to produce poppy straw concentrate (PSC, also known as concentrate of poppy straw, CPS). Dried, the concentrate is a beige to brown powder. It contains salts of various alkaloids, and can range from nine to 30 times the morphine concentration of poppy straw. Opium concentrates using solvents other than acidifed or plain water are often but not necessarily called PSC. Poppies of the Norman and Przemko strains contain much higher amounts of thebaine (also known as paramorphine) and oripavine and have morphine concentrations from as low as below 1% up to 26% that of high-morphine strains.
The biosynthesis of trabectedin in the tunicate symbiotic bacteria Candidatus Endoecteinascidia frumentensis starts with a fatty acid loading onto the acyl-ligase domain of the EtuA3 module. A cysteine and glycine are then loaded as canonical NRPS amino acids. A tyrosine residue is modified by the enzymes EtuH, EtuM1, and EtuM2 to add a hydroxyl at the meta position of the phenol, and adding two methyl groups at the para-hydroxyl and the meta carbon position. This modified tyrosine reacts with the original substrate via a Pictet-Spengler reaction, where the amine group is converted to an imine by deprotonation, then attacks the free aldehyde to form a carbocation that is quenched by electrons from the methyl-phenol ring. This is done in the EtuA2 T-domain. This reaction is done a second time to yield a dimer of modified tyrosine residues that have been further cyclized via Pictet-Spengler reaction, yielding a bicyclic ring moiety. The EtuO and EtuF3 enzymes continue to post-translationally modify the molecule, adding several functional groups and making a sulfide bridge between the original cysteine residue and the beta-carbon of the first tyrosine to form ET-583, ET-597, ET-596, and ET-594 which have been previously isolated. A third O-methylated tyrosine is added and cyclized via Pictet-Spengler to yield the final product.
==== Molecular and signaling response to LTP-inducing stimuli ==== The mechanism for LTP has long been a topic of debate, but, recently, mechanisms have come to some consensus. AMPARs play a key role in this process, as one of the key indicators of LTP induction is the increase in the ratio of AMPAR to NMDARs following high-frequency stimulation. The idea is that AMPARs are trafficked from the dendrite into the synapse and incorporated through some series of signaling cascades. AMPARs are initially regulated at the transcriptional level at their 5' promoter regions. There is significant evidence pointing towards the transcriptional control of AMPA receptors in longer-term memory through cAMP response element-binding protein (CREB) and mitogen-activated protein kinases (MAPK). Messages are translated on the rough endoplasmic reticulum (rough ER) and modified there. Subunit compositions are determined at the time of modification at the rough ER. After post-ER processing in the Golgi apparatus, AMPARs are released into the perisynaptic membrane as a reserve waiting for the LTP process to be initiated. The first key step in the process following glutamate binding to NMDARs is the influx of calcium through the NMDA receptors and the resultant activation of Ca2+/calmodulin-dependent protein kinase (CaMKII). Blocking either this influx or the activation of CaMKII prevents LTP, showing that these are necessary mechanisms for LTP. In addition, profusion of CaMKII into a synapse causes LTP, showing that it is a causal and sufficient mechanism.
The state of war between South Africa and Angola briefly ended with the short-lived Lusaka Accords, but resumed in August 1985 as both PLAN and UNITA took advantage of the ceasefire to intensify their own guerrilla activity, leading to a renewed phase of FAPLA combat operations culminating in the Battle of Cuito Cuanavale. The South African Border War was virtually ended by the Tripartite Accord, mediated by the United States, which committed to a withdrawal of Cuban and South African military personnel from Angola and South West Africa, respectively. PLAN launched its final guerrilla campaign in April 1989. South West Africa received formal independence as the Republic of Namibia a year later, on 21 March 1990. Despite being largely fought in neighbouring states, the South African Border War had a significant cultural and political impact on South African society. The country's apartheid government devoted considerable effort towards presenting the war as part of a containment programme against regional Soviet expansionism and used it to stoke public anti-communist sentiment. It remains an integral theme in contemporary South African literature at large and Afrikaans-language works in particular, having given rise to a unique genre known as grensliteratuur (directly translated "border literature").
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.
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.