This is a working overview of prohibited list, written for readers who want more than a one-paragraph summary but less than a textbook.
Reviewed 2026-04-12. Anything still debated is marked as such rather than presented as 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.
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 |
|---|---|---|
| Common synonyms | Thymosin beta-4 fragment; TB4 fragment | Naming is inconsistent across suppliers and publications |
| Reported sequence | Ac-LKKTETQ | Corresponds to residues 17-23 of the parent protein |
| Frequently cited registry number | 77591-33-4 | Associated with full-length thymosin beta-4 rather than the fragment |
| Common supplied form | Freeze-dried solid | Often presented as an acetate or trifluoroacetate salt |
| Regulatory treatment | Varies by country | Frequently handled as a research chemical; not broadly approved as a therapeutic |
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.
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.
Discussion of the compound frequently appears alongside other short peptides described as fragments of larger proteins. That grouping is convenient but can be misleading, because fragment length, charge, and modification state determine how a peptide behaves in solution and in any experimental system. A seven-residue acetylated peptide and a full-length protein differ in mass by roughly an order of magnitude, and they cannot be assumed to share distribution or binding properties. Precision about which molecule is under discussion is the single most useful step when reading such material.
TB-500 is a shorthand label used in supplier catalogs and online discussion for a short synthetic peptide described as a fragment of thymosin beta-4. Most product listings present it as the N-terminally acetylated heptapeptide Ac-LKKTETQ, a sequence corresponding to the actin-binding region of the parent protein. The name is not a formal chemical designation and does not appear in standard nomenclature systems. Because labeling practices vary between vendors, two products sold under the same name may not contain the same molecule, and the stated sequence should be treated as a claim rather than a fixed definition.
Thymosin beta-4 is a naturally occurring protein of 43 amino acids found in most mammalian cells, where it binds actin monomers and influences filament dynamics. It was first isolated from thymus tissue in the early 1980s, and its actin-binding activity was later mapped to a short region near the N-terminus. The synthetic fragment sold as TB-500 was designed to reproduce that region rather than the full protein. Whether a short fragment reproduces the behavior of the intact molecule remains an open question, since the parent protein carries additional structural elements outside the binding region.
TB-500 is a catalogue name applied to a synthetic peptide related to thymosin beta-4, an actin-binding protein found in most mammalian cells. Suppliers do not use the label consistently: some describe it as the full 43-residue protein, others as a short fragment from the actin-binding region, and others as a related tetrapeptide. Because the name is commercial rather than chemical, two products sold under it may not contain the same molecule. This naming ambiguity is the first point to check in any description of the material.
The most frequently cited identity is a seven-residue fragment with the sequence LKKTETQ, taken from the actin-binding domain of the parent protein. A separate molecule, N-acetyl-seryl-aspartyl-lysyl-proline, often shortened to Ac-SDKP, derives from the same protein's N-terminal region and appears in overlapping literature. Reported molecular masses therefore differ between sources, and a mass value on its own does not establish which fragment is present. Confirmation requires a defined sequence rather than a single number.
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.
On 14 December 1895, there was a large outbreak of botulism in the Belgian village of Ellezelles that occurred at a funeral where people ate pickled and smoked ham; three of them died. By examining the contaminated ham and performing autopsies on the people who died after eating it, van Ermengem isolated an anaerobic microorganism that he called Bacillus botulinus. He also performed experiments on animals with ham extracts, isolated bacterial cultures, and toxins extracts from the bacteria. From these he concluded that the bacteria themselves do not cause foodborne botulism, but rather produce a toxin that causes the disease when ingested. As a result of Kerner's and van Ermengem's research, it was thought that only contaminated meat or fish could cause botulism. This idea was refuted in 1904 when a botulism outbreak occurred in Darmstadt, Germany, because of canned white beans. In 1910, the German microbiologist J. Leuchs published a paper showing that different strains of Bacillus botulinus caused the outbreaks in Ellezelles and Darmstad and that the toxins were serologically distinct. In 1917, Bacillus botulinus was renamed Clostridium botulinum, as it was decided that the term Bacillus should refer to a group of aerobic microorganisms, while Clostridium would be used only to describe a group of anaerobic microorganisms. In 1919, Georgina Burke used toxin-antitoxin reactions to identify two strains of Clostridium botulinum, which she designated A and B.
==== Varieties ==== Koikuchi (濃口; 'thick taste'): Originating in the Kantō region, its usage eventually spread all over Japan. Over 80% of the Japanese domestic soy sauce production is of koikuchi, and can be considered the typical Japanese soy sauce. It is made from roughly equal quantities of soybean and wheat. This variety is also called kijōyu (生醤油) or namashōyu (生しょうゆ) when it is not pasteurized. Usukuchi (薄口; 'thin taste'): Almost 14% of soy sauce production is usukuchi shoyu. It is particularly popular in the Kansai region of Japan. It matures for less time than koichuchi and is both saltier and lighter in color. It is paler due to the use in its production of amazake, a sweet liquid made from fermented rice. Usukuchi is commonly used in cooking as it does not alter the color and taste of the ingredients. Tamari (たまり): Made mainly in the Chūbu region of Japan, tamari is darker in appearance and richer in flavor than koikuchi. It contains little or no wheat. Wheat-free tamari can be used by people with gluten intolerance. Tamari is more viscous than koikuchi shoyu. Of soy sauce produced in Japan, 1.5% is tamari. It is the "original" Japanese soy sauce, as its recipe is closest to the soy sauce originally introduced to Japan from China. Technically, this variety is known as miso-damari (味噌溜り), as this is the liquid that runs off miso (a soybean-based seasoning and soup base) as it matures.
On March 23, the Việt Minh's 316th Division, composed of 11,000 men, with the partly rebuilt 308th and 312th Divisions in reserve, launched an attack on Mạo Khê. With instances of hand-to-hand combat, the French, supported by paratroopers and naval artillery, repelled the attack and the Vietnamese were beaten by the morning of March 28. About 1,500 – 3,000 Việt Minh soldiers were killed. Giáp launched yet another attack, the Battle of the Day River, on May 29 with the 304th Division at Phủ Lý, the 308th Division at Ninh Bình, and the main attack delivered by the 320th Division at Phát Diệm south of Hanoi. The attacks fared no better and the three divisions lost heavily. Taking advantage of this, de Lattre mounted his counteroffensive against the demoralized Việt Minh, driving them back into the forests and eliminating the enemy pockets in the Red River Delta by June 18, costing the Việt Minh over 10,000 killed. Every effort by Võ Nguyên Giáp to break the De Lattre Line failed, and every attack he made was answered by a French counter-attack that destroyed his forces. Việt Minh casualties rose alarmingly during this period, leading some to question the leadership of the Communist government, even within the party. However, any benefit this may have reaped for France was negated by the increasing domestic opposition to the war in France.
The three substrates of this enzyme are benzaldehyde, oxidised nicotinamide adenine dinucleotide (NAD+), and water. Its products are benzoic acid, reduced NADH, and a proton. This enzyme belongs to the family of oxidoreductases, specifically those acting on the aldehyde or oxo group of donor with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is benzaldehyde:NAD+ oxidoreductase. Other names in common use include benzaldehyde (NAD+) dehydrogenase, and benzaldehyde dehydrogenase (NAD+). This enzyme participates in benzoate degradation via hydroxylation and toluene and xylene degradation.
AMPT’s ability to deplete dopamine in the CNS makes it a promising target for treatment of dopamine related disorders. Metirosine is used in scientific research to investigate the effects of catecholamine depletion on behavior. There is evidence that catecholamine depletion causes an increase in sleepiness that is more pronounced than sleep deprivation, and that the fatigue lingers after the drug is discontinued. Catecholamine depletion has also been linked to a negative mood, though this is reported less often than sleepiness.
Sources: en.wikipedia.org
To overcome this effect, a new index was created, named the Equatorial Southern Oscillation Index (EQSOI). To generate this index, two new regions, centered on the Equator, were defined. The western region is located over Indonesia and the eastern one over the equatorial Pacific, close to the South American coast. However, data on EQSOI goes back only to 1949. Sea surface height (SSH) changes up or down by several centimeters in Pacific equatorial region with the ENSO: El Niño causes a positive SSH anomaly (raised sea level) because of thermal expansion while La Niña causes a negative SSH anomaly (lowered sea level) via contraction.
Adalimumab, sold under the brand name Humira and others, is a disease-modifying antirheumatic drug and monoclonal antibody used to treat rheumatoid arthritis, juvenile idiopathic arthritis, psoriatic arthritis, ankylosing spondylitis, Crohn's disease, ulcerative colitis, plaque psoriasis, hidradenitis suppurativa, and uveitis. It is administered by subcutaneous injection (injection under the skin). It works by inactivating tumor necrosis factor (TNF). Common side effects include upper respiratory tract infections, pain at the site of injection, rash, and headache. Other side effects may include serious infections, cancer, anaphylaxis, reactivation of hepatitis B, new onset or exacerbation of demyelinating diseases (such as multiple sclerosis), heart failure, liver failure, and aplastic anemia. Use during pregnancy is not recommended, but some sources show use during breastfeeding may be safe. Adalimumab was approved for medical use in the United States in 2002. It is on the World Health Organization's List of Essential Medicines. It is available as a biosimilar medication. In 2023, it was the 244th most commonly prescribed medication in the United States, with more than 3 million prescriptions.
Nucleases are enzymes that cut DNA strands by catalyzing the hydrolysis of the phosphodiester bonds. Nucleases that hydrolyse nucleotides from the ends of DNA strands are called exonucleases, while endonucleases cut within strands. The most frequently used nucleases in molecular biology are the restriction endonucleases, which cut DNA at specific sequences. For instance, the EcoRV enzyme shown to the left recognizes the 6-base sequence 5′-GATATC-3′ and makes a cut at the horizontal line. In nature, these enzymes protect bacteria against phage infection by digesting the phage DNA when it enters the bacterial cell, acting as part of the restriction modification system. In technology, these sequence-specific nucleases are used in molecular cloning and DNA fingerprinting. Enzymes called DNA ligases can rejoin cut or broken DNA strands. Ligases are particularly important in lagging strand DNA replication, as they join the short segments of DNA produced at the replication fork into a complete copy of the DNA template. They are also used in DNA repair and genetic recombination.
Conventional SSEPs monitor the functioning of the part of the somatosensory system involved in sensations such as touch and vibration. The part of the somatosensory system that transmits pain and temperature signals is monitored using laser evoked potentials (LEP). LEPs are evoked by applying finely focused, rapidly rising heat to bare skin using a laser. In the central nervous system they can detect damage to the spinothalamic tract, lateral brain stem, and fibers carrying pain and temperature signals from the thalamus to the cortex. In the peripheral nervous system pain and heat signals are carried along thin (C and A delta) fibers to the spinal cord, and LEPs can be used to determine whether a neuropathy is located in these small fibers as opposed to larger (touch, vibration) fibers.
The Copenhagen physicists then started a campaign to re-award priority for element 71 to Welsbach and replace the name lutetium with cassiopeium, writing to Welsbach in 1923 of their intentions. This campaign encountered success in the physics literature, but in spite of strong German and Scandinavian support for cassiopeium, lutetium remained embedded in most of the chemical literature, with the International Commission on Atomic Weights in 1930 accepting that element 72 was hafnium but using lutetium for element 71. In 1949, it was decided by the International Union of Pure and Applied Chemistry to recommend the name lutetium, since cassiopeium by then was only used in German and sometimes Dutch, and it was a difficult name to adapt to other languages. It was nonetheless clarified that this was not intended as a statement on priority. Urbain's spelling lutecium was changed to lutetium, in order to derive the name from Latin Lutetia instead of French Lutèce. Pure lutetium metal was first produced in 1953.
Sources: en.wikipedia.org
=== December === 6 December Scientists, for the first time, report a recently discovered area on the current planet Earth, particularly in the Puna de Atacama territory of South America, which may be similar to ancient Earth, and the related environment of the first life forms on Earth – as well as – similar to possibly hospitable conditions on the planet Mars during earlier Martian times. Google DeepMind announces its Gemini multimodal language model, which it claims has advanced "reasoning capabilities" and can outperform GPT-4 on a variety of tasks. 7 December A gene therapy based on three transcription factors, Oct4, Sox2, and Klf4 (OSK), is shown to provide sustained vision recovery in mice affected by glaucoma. Physicists report future proposed plans for the next ten years. These proposals are intended to help better understand some of the current concerns of particle physics, including challenges to the Standard Model, and involve studies primarily dealing with gravity, black holes, dark matter, dark energy, Higgs boson, muons, neutrinos, and more. Quantum entanglement of molecules is achieved for the first time. A comprehensive review of ancient carbon dioxide levels and corresponding temperatures is published by a consortium of more than 80 researchers from 16 nations. Their study finds that current levels of atmospheric carbon dioxide are the highest in at least 14 million years, much longer ago than some existing assessments indicate.
=== Low BMD === Bone Mineral Density (BMD) tends to peak at a young age. When children are younger, they start building up their BMD through their nutrition and through exercise. BMD peaks at around 12.5 years old for girls and around 14 years old for boys. It could be caused by a deficiency in calcium or Vitamin D. Calcium is the main nutrient for bone health. It aids in the structure and density of the bone. Low BMD could be caused by the children not getting the proper exercise for adequate bone growth. Researchers suggest that children should get 20 minutes of vigorous activity 3 to 5 days a week to promote an increase in BMD. Jumping for about 5 minutes a day also stimulates an increase in BMD. Researchers did a 10-year study on the effects of vigorous intensity activity and their bone health/strength. They studied 300 boys and girls. They found that in boys going through puberty (ages 11-13), they experienced a greater bone mass growth. Their bone mass increased during this time because their bones are not ready for the mechanical stress from them growing. However, that is how the bones grow stronger and why their BMD increases. Too much stress on the bones could cause BMD to decrease. Low BMD is dangerous because it can cause disorders inside the bone as the children grow and get older. These disorders can cause the bone to ossify, become brittle, fragile, more easily prone to fractures, and weak. Some of these disorders include osteopenia, osteoporosis, and scoliosis. Scoliosis is very common in children. Low BMD plays a role in the child's scoliosis.
== Etymology == The English name for the element potassium comes from the word potash, which refers to an early method of extracting various potassium salts: placing in a pot the ash of burnt wood or tree leaves, adding water, heating, and evaporating the solution. Humphry Davy named the element potassium after isolating the metal itself. The symbol K stems from kali, itself from the root word alkali, which in turn comes from Arabic: القَلْيَه al-qalyah 'plant ashes'. In 1797, the German chemist Martin Klaproth discovered "potash" in the minerals leucite and lepidolite, and realized that "potash" was not a product of plant growth but actually contained a new element, which he proposed calling kali. In 1807, Humphry Davy produced the element via electrolysis: in 1809, Ludwig Wilhelm Gilbert proposed the name Kalium for Davy's "potassium". In 1814, the Swedish chemist Berzelius advocated the name kalium for potassium, with the chemical symbol K. The English and French-speaking countries adopted the name Potassium, which was favored by Davy and French chemists Joseph Louis Gay-Lussac and Louis Jacques Thénard, whereas the other Germanic countries adopted Gilbert and Klaproth's name Kalium. The "Gold Book" of the International Union of Pure and Applied Chemistry has designated the official chemical symbol as K.
== Personal life == Kahn is married to Susan Becker Kahn, also formerly of Louisville. They have two children. Stacy Anne Kahn is a pediatric gastroenterologist at the Boston Children's Hospital. Jeffrey Adam Kahn is managing partner of Continuum Search based in Denver, Colorado. His brother Arnold Kahn was emeritus professor of developmental biology of the University of California San Francisco.
Sources: en.wikipedia.org
The leading proposal involves sequestration of monomeric actin, which would alter cytoskeletal turnover and cell movement. The actin-binding motif shared with the parent protein is central to that idea. Direct confirmation in whole organisms remains limited.
Very few controlled human studies focus on the seven-residue sequence itself. Most clinical data concern the full-length protein in cardiac or ophthalmic settings. Conclusions drawn for one form should not be assumed to transfer to the other.
Detection normally relies on reversed-phase liquid chromatography paired with mass spectrometry. Chromatographic retention time establishes the expected elution window, and the mass spectrum confirms the molecular ion. Immunoassays exist but can cross-react with related peptides.
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.