The short version of lyophilised powder fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2026-04-07. Anything still debated is marked as such rather than presented as settled.
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.
Once in solution, short peptides are generally less stable than the dry powder, and repeated freeze-thaw cycles are a common cause of loss. Laboratory guidance usually calls for aliquoting on first dissolution and storing aliquots at -20 °C or below, away from light. Adsorption to plastic and glass surfaces can lower measured concentration, particularly at low concentrations, so container material and buffer choice can affect results. Visible cloudiness, colour change or unexpected precipitate is a signal to re-check the material.
Purity is normally assessed by reversed-phase HPLC, with the main peak reported as a percentage of total peak area, while identity is confirmed by mass spectrometry. Electrospray and MALDI-TOF instruments are both used, and the observed mass is compared with the value calculated from the stated sequence. Ion-exchange or size-exclusion methods appear where aggregation or charge variants are of interest. Water content, counter-ion content and residual trifluoroacetate from purification are separate variables that can shift the measured mass and should be weighed when reading a certificate of analysis.
Research peptides are typically supplied as a white to off-white lyophilised powder in a sealed vial. The dry solid is more stable than a solution and is normally kept refrigerated or frozen until use. Dissolution is usually done in water, phosphate-buffered saline or a similar aqueous medium, depending on the assay. Because the material is hygroscopic and easily contaminated, opening vials in a low-humidity environment and recording the lot number before use are standard laboratory practices.
| Property | Value | Notes |
|---|---|---|
| Physical form | Lyophilised powder | Sealed vial; reconstituted before laboratory use |
| Appearance | White to off-white solid | Visual descriptor used on certificates of analysis |
| Solubility class | Water-soluble | Dissolves in water and aqueous buffers |
| Reported mass, fragment | Near 889 Da | Value depends on the stated sequence |
| Reported mass, parent protein | Near 4963 Da | 43-residue thymosin beta-4 |
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.
Full-length thymosin beta-4 consists of roughly forty-three amino acids and ranks among the more abundant small proteins in the cytoplasm. The fragment is much shorter, so it cannot reproduce every function attributed to the intact molecule. In cell culture, short actin-binding motifs can interfere with filament dynamics and cell movement, but such observations come from controlled experiments rather than from whole-animal work. Whether a truncated fragment produces the same effects as the parent protein remains an open question.
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.
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.
=== Cytokines === Cytokines can manipulate neurotransmissions creating sickness behavior, characterized by malaise and fatigue. In animal models, IL-1b stimulates serotonin release and increases activity of GABA. Lipopolysaccharide challenges also inhibit activity of histaminergic and dopaminergic neurons.
Her two manuscripts on form A DNA reached Acta Crystallographica in Copenhagen on 6 March 1953, one day before Crick and Watson had completed their model. The X-ray diffraction images collected by Gosling and Franklin provided the best evidence for the helical nature of DNA. Before this, both Linus Pauling, Watson, and Crick had generated erroneous models with the chains inside and the bases pointing outwards. Her experimental results provided estimates of the water content of DNA crystals, and these results were most consistent with the three sugar-phosphate backbones being on the outside of the molecule. Franklin's X-Ray photograph showed that the backbones had to be on the outside. Although she at first insisted vehemently that her data did not force one to conclude that DNA has a helical structure, in the drafts she submitted in 1953 she argues for a double helical DNA backbone. Building on her manuscripts, she discovered that form A DNA had antiparallel backbones, which supported the double helical structure of DNA. She did this through identification of the space group for DNA crystals. This would go to help Watson and Crick decide to look for DNA models with two antiparallel polynucleotide strands. In summary, Watson and Crick had three sources for Franklin's unpublished data: 1) her 1951 seminar, attended by Watson, 2) discussions with Wilkins, who worked in the same laboratory with Franklin, 3) a research progress report that was intended to promote coordination of Medical Research Council–supported laboratories.
== Research == The first-in-human study, a phase 1 trial, was initiated in October 2017 and completed in September 2020 in postmenopausal women with breast cancer. The study investigated oral doses of vosilasarm of 50 mg/day to 150 mg/day, with the maximum tolerated dose found to be 100 mg/day. A phase 1/2 study proposal of vosilasarm for treatment of breast cancer was published in 2023. It will recruit up to 128 patients.
Portal 2 development was restarted specifically to keep the portal concept but adding new elements to freshen the gameplay. During this period, Valve had witnessed another student project out of DigiPen, Tag: The Power of Paint, which allows the player to spray paint onto surfaces to alter their behavior. The team was brought into Valve, though not initially as part of the Portal franchise. The Tag team had found a way to incorporate their paints with real-time fluid dynamics code previously made by Valve, and the concept became the "conversion gels" found in Portal 2. Valve included a co-operative play mode, based on their own observations and stories from players about working out the solutions to Portal's puzzles in a group environment. With this feature, they sought the ability to enable cross-platform play of Portal 2 between computers and consoles through Steamworks. This led to a surprise reveal by Newell that Portal 2 would be released on the PlayStation 3, despite previously expressing how he felt about the difficulties in supporting the console, and that it would include support for cross-platform play between the PC and PS3 versions through a limited Steamworks interface. Valve brought in writer Jay Pinkerton, who had formerly worked on National Lampoon, as well as Left 4 Dead writer Chet Faliszek to assist Wolpaw with the larger story.
Sources: en.wikipedia.org
==== Tertiary structures ==== Many proteins share analogous structural elements that arose independently across different genomes. There are several examples of convergent protein motifs sharing similar arrangements of structural elements. Whole protein structures too have arisen through convergent evolution.
New Zealand ordered 370 P-51 Mustangs to supplement its F4U Corsairs in the Pacific Ocean Areas theater. Scheduled deliveries were for an initial batch of 30 P-51Ds, followed by 137 more P-51Ds and 203 P-51Ms. The original 30 were being shipped as the war ended in August 1945; these were stored in their packing cases, and the order for the additional Mustangs was canceled. In 1951, the stored Mustangs entered service in 1 (Auckland), 2 (Wellington), 3 (Canterbury), and 4 (Otago) squadrons of the Territorial Air Force (TAF). The Mustangs remained in service until they were prematurely retired in August 1955 following a series of problems with undercarriage and coolant-system corrosion problems. Four Mustangs served on as target tugs until the TAF was disbanded in 1957. RNZAF pilots in the Royal Air Force also flew the P-51 and at least one New Zealand pilot scored victories over Europe while on loan to a USAAF P-51 squadron. Nicaragua The Nicaraguan National Guard purchased 26 P-51D Mustangs from Sweden in 1954 and later received 30 P-51D Mustangs from the US together with two TF-51 models from MAP after 1954. All aircraft of this type were retired from service by 1964. Philippines
The 5-HT3 receptors are a subclass of serotonin (5-HT) receptors. They belong to the Cys-loop superfamily of ligand-gated ion channels (LGICs) and differ structurally and functionally from all other serotonin receptors, which are G protein-coupled receptors. 5-HT3 receptors are cation channels, that is, they are permeable to sodium (Na), potassium (K), and calcium (Ca) ions and mediate neuronal depolarization and excitation within the central and peripheral nervous systems. As with other ligand gated ion channels, the 5-HT3 receptor consists of five subunits arranged around a central ion conducting pore. Binding of the neurotransmitter serotonin (or 5-hydroxytryptamine) to the 5-HT3 receptor opens the channel, which, in turn, leads to an excitatory response in neurons. The rapidly activating, desensitizing, inward current is predominantly carried by sodium and potassium ions. 5-HT3 receptors have a negligible permeability to anions. They are most closely related by homology to the nicotinic acetylcholine receptor.
Sources: en.wikipedia.org
a sequence of elements of the pattern notation matches a sequence of amino acids if and only if the latter sequence can be partitioned into subsequences in such a way that each pattern element matches the corresponding subsequence in turn. Thus the pattern [AB] [CDE] F matches the six amino acid sequences corresponding to ACF, ADF, AEF, BCF, BDF, and BEF. Different pattern description notations have other ways of forming pattern elements. One of these notations is the PROSITE notation, described in the following subsection.
Although for the rest of his career Heseltine's role in Thatcher's downfall earned him enmity from Thatcher's supporters in the Conservative party, this opprobrium was not universal. In a reference to the reluctance of the Cabinet to support Thatcher on the second ballot, Edward Leigh said of Heseltine: "At least he stabbed her in the front". Heseltine believed that he would have defeated Thatcher if she had contested the second ballot. It has been suggested that he should have withdrawn after weakening her on the first ballot, and that he would have been restored to the Cabinet whether or not she continued as prime minister; he writes that this was never seriously suggested at the time.
The mechanism of this sub-type of muscular dystrophy consists of a mutation in the FKTN gene which results in a malformed fukutin protein. It is thought that fukutin modifies the alpha-dystroglycan protein, which is important in anchoring cells to certain molecules, specifically including some proteins. Alpha-dystroglycan in skeletal muscles helps to prevent the breakdown of muscle fibers through stabilization and protection. Alpha-dystroglycan also helps brain development by assisting in the migration of neurons. Most frequently, FKTN is mutated in such a way that creates a shortage of fukutin in the cell, which in turn creates problems during formation of alpha-dystroglycan leading to less stabilization of muscle cells. Use of the destabilized muscle fibers over time causes them to break down and a gradual decline in muscle tone and atrophy of muscle fibers occurs. The decline in cerebral fukutin causes neuronal cells to continue moving beyond their intended destination. Additionally, oxidative stress has some effect on astrocytes (as well as, neurons) when fukutin is subdued.
Sources: en.wikipedia.org
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.
Naming for research peptides is not standardised, and suppliers sometimes apply the same label to different chain lengths. Certificates of analysis and mass data are the practical way to determine what a given lot contains.
The fragment commonly cited under this label is reported near 889 Da, and the parent protein near 4963 Da. Reported values shift with the exact sequence and with residual counter-ions or water in the sample.
Sealed, desiccated and protected from light, at -20 °C or lower for long-term storage. Short-term storage at refrigerator temperature is common in working laboratories.