This is a working overview of lyophilized powder, written for readers who want more than a one-paragraph summary but less than a textbook.
Reviewed 2026-02-17. Anything still debated is marked as such rather than presented as settled.
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.
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.
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.
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.
| 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 |
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.
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.
Interest in the fragment grew during the 1990s and 2000s, when it moved from laboratory work into sports and supplement markets. Anti-doping bodies added thymosin beta-4 fragments to prohibited lists, and a small number of adverse analytical findings have been reported in competition testing. Published controlled human trials remain scarce. Most mechanistic evidence comes from cell culture and animal models, and those studies examine endpoints such as cell migration, wound closure and inflammation markers. That evidence supports research interest but does not establish clinical benefit, and broad regenerative claims should be read as unverified.
TB-500 is a short synthetic peptide sold under a trade name rather than a systematic chemical name. Suppliers usually describe it as a fragment of thymosin beta-4 and ship it as a lyophilised powder intended for laboratory use. Because the label is commercial, the exact sequence attributed to it is not fully consistent across catalogues, and some listings present a seven-residue peptide while others describe related fragments of similar length. It is not an approved medicine in any major jurisdiction, and it is handled as a research chemical.
=== Transmission === Scabies is contagious and can be contracted through prolonged physical contact with an infested person. This includes sexual intercourse, although a majority of cases are acquired through other forms of skin-to-skin contact. Less commonly, scabies infestation can happen through the sharing of clothes, towels, and bedding, but this is not a major mode of transmission; individual mites can survive for only two to three days, at most, away from human skin at room temperature. As with lice, a latex condom is ineffective against scabies transmission during intercourse, because mites typically migrate from one individual to the next at sites other than the sex organs. Multiple transmission factors allow scabies to achieve very high prevalence rates in institutional outbreaks, including crowded living conditions with high host density, social interactions involving prolonged skin-to-skin contact, sharing of bedding and clothing, frequent manual handling, limited access to laundry services, and immunocompromised populations. Healthcare workers are at risk of contracting scabies from patients, because they may be in extended contact with them.
GOT1/cAST, the cytosolic isoenzyme derives mainly from red blood cells and heart. GOT2/mAST, the mitochondrial isoenzyme is present predominantly in liver. These isoenzymes are thought to have evolved from a common ancestral AST via gene duplication, and they share a sequence homology of approximately 45%. AST has also been found in a number of microorganisms, including E. coli, H. mediterranei, and T. thermophilus. In E. coli, the enzyme is encoded by the aspCgene and has also been shown to exhibit the activity of an aromatic-amino-acid transaminase (EC 2.6.1.57).
The fission of one atom of uranium-235 releases 202.5 MeV (3.24×10−11 J) inside the reactor. That corresponds to 19.54 TJ/mol, or 83.14 TJ/kg. Another 8.8 MeV escapes the reactor as anti-neutrinos. When 23592U nuclei are bombarded with neutrons, one of the many fission reactions that it can undergo is the following (shown in the adjacent image):
== Medical uses == Saxagliptin is used as monotherapy or in combination with other drugs for the treatment of type 2 diabetes. It does not appear to decrease the risk of heart attacks or strokes. One study showed a 3.5% risk of hospitalization for heart failure compared to 2.8% in a placebo-controlled group. Like other DPP-4 inhibitors, it has relatively modest HbA1c lowering ability, is associated with a relatively low risk of hypoglycemia, and does not cause weight gain. Saxagliptin improved mean HbA1c levels (relative to placebo) in a 24-week trial in people with type 2 diabetes. Combination therapy with saxagliptin and metformin was more effective than saxagliptin or metformin monotherapy. When the relative benefits of increasing the dose of a sulfonylurea or adding saxagliptin were assessed in a study of 768 patients, combination treatments were shown to have a significantly greater impact on fasting blood glucose than increasing the tested glibenclamide dose alone.
Sources: en.wikipedia.org
At the start of 1944, Major General James Doolittle, the new commander of the 8th Air Force, released most fighters from the requirement of flying in close formation with the bombers, allowing them free rein to attack the Luftwaffe wherever it could be found. The aim was to achieve air supremacy. Mustang groups were sent far ahead of the bombers in a "fighter sweep" to intercept German fighters. Bomber crews complained, but by June, supremacy was achieved. The Luftwaffe's twin-engined Messerschmitt Bf 110 Zerstörer heavy fighters brought up to deal with the bombers proved to be easy prey for the Mustangs, and had to be quickly withdrawn from combat. The Focke-Wulf Fw 190A, already suffering from poor high-altitude performance, was outperformed by the Mustang at the B-17's altitude, and when laden with heavy bomber-hunting weapons and extra armor as a replacement for the more vulnerable twin-engined Zerstörer heavy fighters, these variants had poor manuverability and suffered heavy losses. The Messerschmitt Bf 109 had comparable performance to the P-51 at high altitudes, but its lightweight airframe was even more affected by increases in armament. The Luftwaffe answered with the Gefechtsverband ("battle formation"). This consisted of a Sturmgruppe of heavily armed and armored Fw 190As escorted by two Begleitgruppen of Bf 109s, whose task was to keep the Mustangs away from the Fw 190s as they attacked the bombers. This strategy proved to be problematic, as the large German formation took a long time to assemble and was difficult to maneuver.
==== MeSH D12.125.166 – amino acids, sulfur ==== MeSH D12.125.166.175 – cystathionine MeSH D12.125.166.215 – cysteic acid MeSH D12.125.166.230 – cysteine MeSH D12.125.166.230.259 – acetylcysteine MeSH D12.125.166.230.310 – carbocysteine MeSH D12.125.166.230.330 – cysteinyldopa MeSH D12.125.166.230.369 – cystine MeSH D12.125.166.230.700 – selenocysteine MeSH D12.125.166.388 – ethionine MeSH D12.125.166.498 – homocysteine MeSH D12.125.166.498.050 – s-adenosylhomocysteine MeSH D12.125.166.554 – homocystine MeSH D12.125.166.676 – methionine MeSH D12.125.166.676.180 – s-adenosylmethionine MeSH D12.125.166.676.450 – n-formylmethionine MeSH D12.125.166.676.450.440 – n-formylmethionine leucyl-phenylalanine MeSH D12.125.166.676.620 – methionine sulfoximine MeSH D12.125.166.676.620.125 – buthionine sulfoximine MeSH D12.125.166.676.900 – selenomethionine MeSH D12.125.166.676.950 – vitamin u MeSH D12.125.166.786 – penicillamine MeSH D12.125.166.786.500 – s-nitroso-n-acetylpenicillamine MeSH D12.125.166.800 – thiopronine MeSH D12.125.166.893 – thiorphan
See polycythemia vera for management of primary polycythemia, which involves reducing thrombotic risk, symptom amelioration and monitoring for further hematologic complications. Treatment can include phlebotomy, aspirin, and myelosuppressive or cytoreductive medications based on risk stratification. For secondary polycythemia, management involves addressing the underlying etiology of increased erythropoeitin production, such as smoking cessation, CPAP for sleep apnea, or removing any EPO-producing tumours. Phlebotomy is not typically recommended for patients with physiologic polycythemia, who rely on additional red cell mass for necessary oxygen delivery, unless the patient is clearly symptomatic and experiences relief from phlebotomy. It is unclear if patients with secondary polycythemia are at elevated thrombotic risk, but aspirin can be considered for patients at elevated cardiovascular risk or for patients with Chuvash polycythemia. The first-line treatment for post-transplant erythrocytosis specificity is angiotensin-converting enzyme (ACE) inhibitors or angiotensin receptor blockers.
== Epidemiology == Anorexia is estimated to occur in 0.9–4.3% of women and 0.2–0.3% of men in Western countries at some point in their life. About 0.4% of young females are affected in a given year and it is estimated to occur three to ten times less commonly in males. The cause of this disparity is not well-established but is thought to be linked to both biological and socio-cultural factors. Rates in most of the developing world are unclear. Often it begins during the teen years or young adulthood. Medical students are a high risk group, with an overall estimated prevalence of 10.4% globally. The lifetime rate of atypical anorexia nervosa, a form of ED-NOS in which the person loses a significant amount of weight and is at risk for serious medical complications despite having a higher body-mass index, is much higher, at 5–12%. Additionally, a UCSF study showed severity of illness is independent of current BMI, and "patients with large, rapid, or long-duration of weight loss were more severely ill regardless of their current weight." While anorexia became more commonly diagnosed during the 20th century it is unclear if this was due to an increase in its frequency or simply better diagnosis. Most studies show that since at least 1970 the incidence of AN in adult women is fairly constant, while there is some indication that the incidence may have been increasing for girls aged between 14 and 20.
From July 1, 2025, through the March 3, 2026 primary, $120,721.54 in itemized receipts attributed to Rourk's campaign were identified in Federal Election Commission records, including $26,435.29 in contributions from Rourk herself. Of the remaining $94,286.25 in itemized contributions from other individuals, $75,521.25 (80.1%) came from contributors outside the district, including $47,436.25 from outside Texas and $28,085 from Texas contributors outside the district. In-district contributors accounted for $18,765 of those individual contributions.
Sources: en.wikipedia.org
=== Formation === There are several hypotheses proposed regarding the formation of Tarlov cysts, including: hemorrhagic infiltration of spinal tissue, inflammation within the nerve root cysts followed by inoculation of fluids, developmental or congenital origin, arachnoidal proliferation along and around the exiting sacral nerve root, and breakage of venous drainage in the perineuria and epineurium secondary to hemosiderin deposition after trauma. Tarlov himself theorized that the perineural cysts form as a result of blockage of venous drainage in the perineurium and epineurium secondary to hemosiderin deposition, after local trauma. Another theory gaining increasing popularity, over the past decade, is one postulated by Fortuna et al.; it described perineural cysts to be the results of congenital arachnoidal proliferation along the exiting sacral nerve roots. Some research on the migration of inflammatory cell into spinal has been studied. Additionally, in vivo and in vitro studies show inflammation induced by CNS injury causes distinct cystic cavitations created by astrocyte migration.
== Interpreting results == The Ka/Ks ratio is used to infer the direction and magnitude of natural selection acting on protein coding genes. A ratio greater than 1 implies positive or Darwinian selection (driving change); less than 1 implies purifying or stabilizing selection (acting against change); and a ratio of exactly 1 indicates neutral (i.e. no) selection. However, a combination of positive and purifying selection at different points within the gene or at different times along its evolution may cancel each other out. The resulting averaged value can mask the presence of one of the selections and lower the seeming magnitude of another selection. Of course, it is necessary to perform a statistical analysis to determine whether a result is significantly different from 1, or whether any apparent difference may occur as a result of a limited data set. The appropriate statistical test for an approximate method involves approximating dN − dS with a normal approximation, and determining whether 0 falls within the central region of the approximation. More sophisticated likelihood techniques can be used to analyse the results of a Maximum Likelihood analysis, by performing a chi-squared test to distinguish between a null model (Ka/Ks = 1) and the observed results.
Astatine-210 and most of the lighter isotopes exhibit beta plus decay (positron emission), astatine-217 and heavier isotopes except astatine-218 exhibit beta minus decay, while astatine-211 undergoes electron capture. The most stable isotope is astatine-210, which has a half-life of 8.1 hours. The primary decay mode is beta plus, to the relatively long-lived (in comparison to astatine isotopes) alpha emitter polonium-210. In total, only five isotopes have half-lives exceeding one hour (astatine-207 to -211). The least stable ground state isotope is astatine-213, with a half-life of 125 nanoseconds. It undergoes alpha decay to the extremely long-lived bismuth-209. Astatine has 24 known nuclear isomers, which are nuclei with one or more nucleons (protons or neutrons) in an excited state. A nuclear isomer may also be called a "meta-state", meaning the system has more internal energy than the "ground state" (the state with the lowest possible internal energy), making the former likely to decay into the latter. There may be more than one isomer for each isotope. The most stable of these nuclear isomers is astatine-202m1, which has a half-life of about 3 minutes, longer than those of all the ground states bar those of isotopes 203–211 and 220. The least stable is astatine-213m1; its half-life of 110 nanoseconds is shorter than 125 nanoseconds for astatine-213, the shortest-lived ground state.
Natural proteins can be engineered, for example, by directed evolution, novel protein structures that match or improve on the functionality of existing proteins can be produced. One group generated a helix bundle that was capable of binding oxygen with similar properties as hemoglobin, yet did not bind carbon monoxide. A similar protein structure was generated to support a variety of oxidoreductase activities while another formed a structurally and sequentially novel ATPase. Another group generated a family of G-protein coupled receptors that could be activated by the inert small molecule clozapine N-oxide but insensitive to the native ligand, acetylcholine; these receptors are known as DREADDs. Novel functionalities or protein specificity can also be engineered using computational approaches. One study was able to use two different computational methods: a bioinformatics and molecular modeling method to mine sequence databases, and a computational enzyme design method to reprogram enzyme specificity. Both methods resulted in designed enzymes with greater than 100 fold specificity for production of longer chain alcohols from sugar. Another common investigation is expansion of the natural set of 20 amino acids. Excluding stop codons, 61 codons have been identified, but only 20 amino acids are coded generally in all organisms. Certain codons are engineered to code for alternative amino acids including: nonstandard amino acids such as O-methyl tyrosine; or exogenous amino acids such as 4-fluorophenylalanine.
John Kampfner, author, broadcaster and commentator; executive director at Chatham House; has written and presented for Reuters, The Daily Telegraph; chief political correspondent at the Financial Times; political commentator for BBC's Today radio programme; political correspondent on Newsnight; was chair of the Clore Duffield Foundation, Council of King's College London; Chief Executive of the freedom of expression organisation Index on Censorship and established Creative Industries Federation; shortlisted for the Orwell Book prize. Efraim Karsh (born 6 September 1953) British-Israeli historian at King's College London; director of political studies Bar-Ilan University the Begin-Sadat Center for Strategic Studies).; former director of Middle East Forum; held posts at Harvard, Columbia universities, Sorbonne, London School of Economics, Helsinki University, International Institute for Strategic Studies, Kennan Institute for Advanced Russian Studies in Washington D.C., and Jaffee Center for Strategic Studies at Tel Aviv University; in 1989 joined King's College London; has contributed articles to The New York Times, The Los Angeles Times, The Wall Street Journal, The Times (London) and The Daily Telegraph. His book Palestine Betrayed argued that 1948 Palestinian expulsion and flight was "exclusively of their own making".
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.
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.