If you have been reading about actin binding 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.
Updated 2025-10-01. Numbers and descriptions here follow the published literature rather than marketing material.
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.
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.
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.
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.
| 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 |
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.
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.
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.
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.
== History == Pyridoxine was discovered in 1934, isolated in 1938, and first made in 1939. It is on the World Health Organization's List of Essential Medicines. Pyridoxine is available both as a generic medication and over the counter product. Foods, such as breakfast cereal have pyridoxine added in some countries.
== Short-term feed restriction == Recent studies on short-term effects of a meal or the absence of a meal has revealed that lepa1 expression specifically peaks in the peripheral tissues after 6 – 9 hr in the unfed fish. This suggests that the transcript specific response could be associated with the absence of food. Conversely, since the unfed fish had not received food for 33 hr (24 + 9 hr), the peaks could represent an unrelated effect. Each lepa1 peak occurred during a phase of falling plasma Lep, and since this occurred in both fed and unfed fish, the temporal upregulation of lepa1 does not in fact appear to be specifically related to the absence of food. The earliest peak of lepa1 occurred in the white muscle, which represents an important lipid reservoir in Atlantic salmon. Unlike pufferfish, which utilizes the liver as a major lipid repository, Atlantic salmon shows that despite a high visceral lipid content, hepatocytes contain few lipid droplets compared to other fish species, yet are an important site for leptin expression. Moen and colleagues reported that both lepa1 and lepa2 peaked at 9 hr in the liver of unfed fish. By contrast, however, studies in common carp demonstrated a peak in leptin-I(lepa1) and leptin–II (lepa2) in liver at 3 and 6 hr post feeding respectively. The earlier expression response of leptins in common carp likely reflects the higher temperature under which the experiments were conducted, but contrasts the findings of upregulation of lepa1 due to the absence of food.
As radioactive iodine treatment results in the destruction of thyroid tissue, there is often a transient period of several days to weeks when the symptoms of hyperthyroidism may worsen following radioactive iodine therapy. In general, this happens as a result of thyroid hormones being released into the blood following the radioactive iodine-mediated destruction of thyroid cells that contain thyroid hormone. In some people, treatment with medications such as beta blockers (propranolol, atenolol, etc.) may be useful during this period. Most people do not experience any difficulty after the radioactive iodine treatment, usually given as a small pill. On occasion, neck tenderness or a sore throat may become apparent after a few days, if moderate inflammation in the thyroid develops and produces discomfort in the neck or throat area. This is usually transient, and not associated with a fever, etc. It is recommended that breastfeeding be stopped at least six weeks before radioactive iodine treatment and that it not be resumed, although it can be done in future pregnancies. It also shouldn't be done during pregnancy, and pregnancy should be put off until at least 6–12 months after treatment. A common outcome following radioiodine is a swing from hyperthyroidism to easily treatable hypothyroidism, which occurs in 78% of those treated for Graves' thyrotoxicosis and in 40% of those with toxic multinodular goiter or solitary toxic adenoma.
NADH:ubiquinone reductase (non-electrogenic) (EC 1.6.5.9, NDH-2, ubiquinone reductase, coenzyme Q reductase, dihydronicotinamide adenine dinucleotide-coenzyme Q reductase, DPNH-coenzyme Q reductase, DPNH-ubiquinone reductase, NADH-coenzyme Q oxidoreductase, NADH-coenzyme Q reductase, NADH-CoQ oxidoreductase, NADH-CoQ reductase) is an enzyme with systematic name NADH:ubiquinone oxidoreductase. This enzyme catalyses the following chemical reaction:
Two black spots (ocelli) can be found on each side of the white or orangish nape. The function of these spots is debated, but the most commonly accepted theory is that they act as "false eyes", and help to protect the bird from potential attackers.
Sources: en.wikipedia.org
Gearbox Software, L.L.C. is an American video game development company based in Frisco, Texas. It was established as a limited liability company in February 1999 by five developers formerly of Rebel Boat Rocker. Randy Pitchford, one of the founders, serves as president and chief executive officer. Gearbox initially created expansions for the Valve game Half-Life, then ported that game and others to console platforms. In 2005, Gearbox launched its first independent set of games, Brothers in Arms, on console and mobile devices. It became its flagship franchise and spun off a comic book series, television documentary, books, and action figures. Their second original game series, Borderlands, commenced in 2009, and by 2015 had sold over 26 million copies. The company also owns the intellectual property of Duke Nukem and Homeworld. Gearbox expanded into publishing with the creation of Gearbox Publishing in 2015. A parent company, The Gearbox Entertainment Company, was established for Gearbox Software and Gearbox Publishing in 2019. Gearbox Entertainment was acquired by the Embracer Group in April 2021, becoming its seventh major label. A third division, Gearbox Studios, focusing on television and film productions, was established in October 2021. Due to major restructuring following a failed investment, Embracer announced plans to divest Gearbox to Take-Two Interactive, who had previously published several of Gearbox's games under its 2K label, in March 2024. Take-Two Interactive closed the Gearbox Software acquisition on June 12, 2024.
=== Biosecurity and bioterrorism === Some ethical issues relate to biosecurity, where biosynthetic technologies could be deliberately used to cause harm to society and/or the environment. Since synthetic biology raises ethical issues and biosecurity issues, humanity must consider and plan on how to deal with potentially harmful creations, and what kinds of ethical measures could possibly be employed to deter nefarious biosynthetic technologies. With the exception of regulating synthetic biology and biotechnology companies, however, the issues are not seen as new because they were raised during the earlier recombinant DNA and genetically modified organism (GMO) debates, and extensive regulations of genetic engineering and pathogen research are already in place in many jurisdictions. Additionally, the development of synthetic biology tools has made it easier for individuals with less education, training, and access to equipment to modify and use pathogenic organisms as bioweapons. This increases the threat of bioterrorism, especially as terrorist groups become aware of the significant social, economic, and political disruption caused by pandemics like COVID-19. As new techniques are developed in the field of synthetic biology, the risk of bioterrorism is likely to continue to grow.
=== BLOSUM === Dayhoff's methodology of comparing closely related species turned out not to work very well for aligning evolutionarily divergent sequences. Sequence changes over long evolutionary time scales are not well approximated by compounding small changes that occur over short time scales. The BLOSUM (BLOck SUbstitution Matrix) series of matrices rectifies this problem. Henikoff & Henikoff constructed these matrices using multiple alignments of evolutionarily divergent proteins. The probabilities used in the matrix calculation are computed by looking at "blocks" of conserved sequences found in multiple protein alignments. These conserved sequences are assumed to be of functional importance within related proteins and will therefore have lower substitution rates than less conserved regions. To reduce bias from closely related sequences on substitution rates, segments in a block with a sequence identity above a certain threshold were clustered, reducing the weight of each such cluster (Henikoff and Henikoff). For the BLOSUM62 matrix, this threshold was set at 62%. Pairs frequencies were then counted between clusters, hence pairs were only counted between segments less than 62% identical. One would use a higher numbered BLOSUM matrix for aligning two closely related sequences and a lower number for more divergent sequences. It turns out that the BLOSUM62 matrix does an excellent job detecting similarities in distant sequences, and this is the matrix used by default in most recent alignment applications such as BLAST.
== History == Erythritol was discovered in 1848 by the Scottish chemist John Stenhouse and first isolated in 1852. Starting from 1945, American chemists applied newly-developed techniques of chromatography to sugarcane juice and blackstrap molasses, finding in 1950 that erythritol was present in molasses fermented by yeast. It was first approved and marketed as a sweetener in Japan in 1990, and in the US in 1997. In February 1997, Cerestar Holding Co., Mitsubishi Chemical Co., and Nikken Chemicals Co. submitted a formal generally recognized as safe (GRAS) affirmation petition with the US FDA. However, in April 1997 the FDA replaced the GRAS affirmation petition process with the current GRAS notification process, a notice was first filed by Cerestar in April 2001, and the FDA responded with "no questions" in September 2001.
==== Groundwater ==== In saturated groundwater aquifers, all available pore spaces are filled with water (volumetric water content = porosity). Above a capillary fringe, pore spaces have air in them too. Most soils have a water content less than porosity, which is the definition of unsaturated conditions, and they make up the subject of vadose zone hydrogeology. The capillary fringe of the water table is the dividing line between saturated and unsaturated conditions. Water content in the capillary fringe decreases with increasing distance above the phreatic surface. The flow of water through and unsaturated zone in soils often involves a process of fingering, resulting from Saffman–Taylor instability. This results mostly through drainage processes and produces and unstable interface between saturated and unsaturated regions. One of the main complications which arises in studying the vadose zone, is the fact that the unsaturated hydraulic conductivity is a function of the water content of the material. As a material dries out, the connected wet pathways through the media become smaller, the hydraulic conductivity decreasing with lower water content in a very non-linear fashion. A water retention curve is the relationship between volumetric water content and the water potential of the porous medium. It is characteristic for different types of porous medium. Due to hysteresis, different wetting and drying curves may be distinguished.
Sources: en.wikipedia.org
Statistical methods, such as significance tests and confidence intervals, which can be interpreted in terms of the frequency of certain outcomes occurring in hypothetical repeated realisations of the same experimental situation. (ICH E9) Full analysis set
=== South America === The soybean first arrived in South America in Argentina in 1882. Andrew McClung showed in the early 1950s that with soil amendments the Cerrado region of Brazil would grow soybeans. In June 1973, when soybean futures markets mistakenly portended a major shortage, the Nixon administration imposed an embargo on soybean exports. It lasted only a week, but Japanese buyers felt that they could not rely on U.S. supplies, and the rival Brazilian soybean industry came into existence. This led Brazil to become the world's largest producer of soybeans in 2020, with 131 million tons. Industrial soy production in South America is characterized by wealthy management who live far away from the production site which they manage remotely. In Brazil, these managers depend heavily on advanced technology and machinery, and agronomic practices such as zero tillage, high pesticide use, and intense fertilization. One contributing factor is the increased attention on the Brazilian Cerrado in Bahia, Brazil by US farmers in the early 2000s. This was due to rising values of scarce farmland and high production costs in the US Midwest. There were many promotions of the Brazilian Cerrado by US farm producer magazines and market consultants who portrayed it as having cheap land with ideal production conditions, with infrastructure being the only thing it was lacking. These same magazines also presented Brazilian soy as inevitably out-competing American soy. Another draw to investing was the insider information about the climate and market in Brazil.
Geddy Lee's high-register vocal style has always been a signature of the band–and sometimes a focal point for criticism, especially during the early years of Rush's career when his vocals were high-pitched, with a strong likeness to other singers like Robert Plant of Led Zeppelin. A review in The New York Times opined that Lee's voice "suggests a munchkin giving a sermon". Although his voice has softened, it is often described as a "wail". His instrumental abilities, on the other hand are rarely criticized. He has cited Jeff Berlin, Jack Casady, John Entwistle, Jack Bruce and Chris Squire as being the bassists who had the biggest impact on his playing style. Lee's style, technique, and ability on the bass guitar have been influential to rock and heavy metal musicians, inspiring players including Steve Harris, John Myung, Les Claypool, and Cliff Burton. Lee is able to operate various pieces of instrumentation simultaneously during concerts, most evidently when he plays bass and keyboards, sings, and triggers foot pedals as in the song "Tom Sawyer".
=== Post-classical development === During the Middle Ages, the word "anarchia" came into use in Latin, in order to describe the eternal existence of the Christian God. It later came to reconstitute its original political definition, describing a society without government. Christian theologists came to claim that all humans were inherently sinful and ought to submit to the omnipotence of higher power, with the French Protestant reformer John Calvin declaring that even the worst form of tyranny was preferable to anarchy. The Scottish Quaker Robert Barclay also denounced the "anarchy" of libertines such as the Ranters. In contrast, radical Protestants such as the Diggers advocated for anarchist societies based on common ownership. Although following attempts to establish such a society, the Digger Gerard Winstanley came to advocate for an authoritarian form of communism. During the 16th century, the term "anarchy" first came into use in the English language. It was used to describe the disorder that results from the absence of or opposition to authority, with John Milton writing of "the waste/Wide anarchy of Chaos" in Paradise Lost. Initially used as a pejorative descriptor for democracy, the two terms began to diverge following the Atlantic Revolutions, when democracy took on a positive connotation and was redefined as a form of elected, representational government.
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.
No. TB-500 is a trade-style label used for a synthetic peptide described as a fragment of thymosin beta-4, while thymosin beta-4 is the full 43-residue protein. The two differ in size and are not interchangeable terms in analytical work.