TB-500 comes up often in conversation and rarely with the context attached. Here we lay out the basics in order, then work through the practical considerations.
Updated 2025-12-12. 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.
| 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.
Nevertheless, all methods aforementioned have been associated with limited cardiac function improvements and limited cell survival once implanted in the fibrous myocardium. To resume, stem cells and delivery routes aforementioned are suitable for cardiomyoplasty as demonstrated safe with some degree of benefit for the patient. However, cardiac remodelling remains limited due to limited cell residency, impact of mechanical forces onto cell survival and tissue hypoxia. Furthermore, lack of cellular electrochemical coupling can lead to arrhythmias. Another point of consideration concerns the use of embryonic stem cells, whereby indifferentiation yields uncontrolled proliferation and possible consequent formation of teratomas. Also iPSCs have been associated with viral infection and eventual oncogenicity. Cardiac tissue engineering is a new technology based on the use of combinations of cells with regenerative capacity, biological and/or synthetic materials, cell signaling agents to induce the regeneration of an organ or damaged tissue. In an ideal scenario, regenerated tissue would reproduce sophisticated asymmetric helicodoidal architecture of the myocardium with the production of specialized extracellular matrix to stimulate vascularization in the implanted tissue. From a cellular perspective, available techniques are monolayer cell construct onto temperature-sensitive polymer, where their detachment is driven by behavior of the mechanical properties of the synthetic support without the need of any enzymatic digestion such as trypsin.
An orphan drug is a pharmaceutical agent that is developed to treat certain rare medical conditions. An orphan drug would not be profitable to produce without government assistance, due to the small population of patients affected by the conditions. The conditions that orphan drugs are used to treat are referred to as orphan diseases. The assignment of orphan status to a disease and to drugs developed to treat it is a matter of public policy that depends on the legislation (if there is any) of the country. Designation of a drug as an orphan drug has yielded medical breakthroughs that might not otherwise have been achieved, due to the economics of drug research and development. For example, in the U.S. and the EU, it is easier to gain marketing approval for an orphan drug. There may be other financial incentives, such as an extended period of exclusivity, during which the producer has sole rights to market the drug. All are intended to encourage development of drugs which would otherwise lack sufficient profit motive to attract corporate research budgets and personnel.
===== S-GlcNAc ===== Mass spectrometry identified S-GlcNAc as a post-translational modification found on cysteine residues. In vitro experiments demonstrated that OGT could catalyze the formation of S-GlcNAc and that OGA is incapable of hydrolyzing S-GlcNAc. Though a previous report suggested that OGA is capable of hydrolyzing thioglycosides, this was only demonstrated on the aryl thioglycoside para-nitrophenol-S-GlcNAc; para-nitrothiophenol is a more activated leaving group than a cysteine residue. Recent studies have supported the use of S-GlcNAc as an enzymatically stable structural model of O-GlcNAc that can be incorporated through solid-phase peptide synthesis or site-directed mutagenesis.
== History == Oxymorphone was first developed in Germany in 1914, and patented in the US by Endo Pharmaceuticals in 1955. It was introduced in the United States in January 1959 and other countries around the same time.
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A coronary occlusion, or coronary artery disease, is the partial or complete obstruction of blood flow in a coronary artery. This condition was first discussed in 1910 by Sir William Osler. This condition slows or blocks the supply of oxygen-rich blood to the heart. This condition can lead to myocardial ischemia and if untreated, may cause a heart attack and heart failure. It is the most common form of cardiovascular disease, and is the leading cause of death in the United States, affecting 18 million adults or about 5% of the population.
It is typical to record spectrum of both the sample and a "reference". This step controls for a number of variables, e.g. infrared detector, which may affect the spectrum. The reference measurement makes it possible to eliminate the instrument influence. The appropriate "reference" depends on the measurement and its goal. The simplest reference measurement is to simply remove the sample (replacing it by air). However, sometimes a different reference is more useful. For example, if the sample is a dilute solute dissolved in water in a beaker, then a good reference measurement might be to measure pure water in the same beaker. Then the reference measurement would cancel out not only all the instrumental properties (like what light source is used), but also the light-absorbing and light-reflecting properties of the water and beaker, and the final result would just show the properties of the solute (at least approximately). A common way to compare to a reference is sequentially: first measure the reference, then replace the reference by the sample and measure the sample. This technique is not perfectly reliable; if the infrared lamp is a bit brighter during the reference measurement, then a bit dimmer during the sample measurement, the measurement will be distorted. More elaborate methods, such as a "two-beam" setup (see figure), can correct for these types of effects to give very accurate results. The Standard addition method can be used to statistically cancel these errors.
The world's longest hot dog had been 60 meters (197 ft) long and rested within a 60.3-meter (198 ft) bun. The hot dog was prepared by Shizuoka Meat Producers for the All-Japan Bread Association, which baked the bun and coordinated the event, including official measurement for the world record. The hot dog and bun were the center of a media event in celebration of the Association's 50th anniversary on August 4, 2006, at the Akasaka Prince Hotel in Tokyo. On May 31, 2012, Guinness World Records certified the world record for the most expensive hot dog at US$145.49. The "California Capitol City Dawg", served at Capitol Dawg in Sacramento, California, features a grilled 460 mm (18 in) all-beef, natural-casing frank from Chicago, served on a fresh-baked herb-and-oil focaccia roll, spread with white truffle butter, then grilled. It is topped with whole-grain mustard from France, garlic and herb mayonnaise, sauteed chopped shallots, organic mixed baby greens, maple syrup-marinated and fruitwood-smoked uncured bacon from New Hampshire, chopped tomato, moose cheese from Sweden, sweetened dried cranberries, basil olive oil and pear-cranberry-coconut balsamic vinaigrette, and ground peppercorn. Proceeds from the sale of each 1.4 kg (3 lb) super dog were donated to the Shriners Hospitals for Children. Hot dogs are a popular food for eating competitions. The record for hot dogs eaten in 10 minutes is 83 by Joey Chestnut at the "Chestnut vs. Kobayashi: Unfinished Beef" event on September 2, 2024. The last person to hold the record before Chestnut was Takeru Kobayashi.
== Applications == Cysteine, mainly the l-enantiomer, is a precursor in the food, pharmaceutical, and personal-care industries. One of the largest applications is the production of flavors. For example, the reaction of cysteine with sugars in a Maillard reaction yields meat flavors. l-Cysteine is also used as a processing aid for baking. In the field of personal care, cysteine is used for permanent-wave applications, predominantly in Asia. Again, the cysteine is used for breaking up the disulfide bonds in the hair's keratin. Cysteine is a very popular target for site-directed labeling experiments to investigate biomolecular structure and dynamics. Maleimides selectively attach to cysteine using a covalent Michael addition. Site-directed spin labeling for EPR or paramagnetic relaxation-enhanced NMR also uses cysteine extensively.
== History == The 5-HT2c receptor agonist Fenfluramine (market names Pondimin, Ponderax and Adifax) was discovered in 1972 as a result of research performed to identify anorectic compounds lacking the effects of psycho-stimulants and sympathomimetic agents (such as amphetamines). Prior to the discovery of fenfluramine, amphetamines were the primary form of anorectic drugs available, however the side effects made them difficult to use. Fenfluramine's anorectic effect is achieved through an increase in serotonin levels, imparting a sensation of fullness, which leads to a lower intake of food. Fenfluramine was sold as a racemic mixture of two enantiomers, dexfenfluramine and levofenfluramine. In 1994, sales of the combination drug Fen-phen (fenfluramine and phentermine) increased dramatically, as this combination produced substantial and apparent synergistic effect in promoting weight loss. Subsequently, reports of severe side effects associated with heart valve abnormalities and an increased risk of pulmonary hypertension resulted in a decision to remove products containing fenfluramine from the U.S. market, and then from other markets around the world. Dexfenfluramine inhibits serotonin reuptake, stimulating the release of serotonin. In 1996, dexfenfluramine became the first long-term treatment anti-obesity medication approved in the US; adverse effects observed during clinical trials included dry mouth, diarrhea and drowsiness. In the mid-1990s the US FDA approved dexfenfluramine as a weight loss drug.
Sources: en.wikipedia.org
=== Mitral stenosis === Chest x-ray in mitral stenosis will typically show an enlarged left atrium, and may show dilation of the pulmonary veins. ECG can show left atrial enlargement, due to increased pressures in the left atrium. Echocardiography is helpful in determining the severity of the disease by estimating the pulmonary artery systolic pressure. This test can also show leaflet calcification and the pressure gradient over the mitral valve. Severe mitral stenosis is defined as a mitral valve area <1.5 cm2. Progressive mitral stenosis has a normal valve area but will have increased flow velocity across the mitral valve.
Pending the resolution of litigation, the Cherokee Freedman had all rights as full Cherokee Nation citizens, including voting rights and access to tribal services. In early 2011, the tribal district court ruled that the special election in 2007 on the constitutional amendment was unconstitutional, as it excluded Freedmen from voting. The Nation appealed. On August 22, 2011, the Cherokee Supreme Court upheld the results of the 2007 special election. Chuck Trimble, a former executive director of the National Congress of American Indians, characterized the decision as the "Cherokee Dred Scott Decision", for depriving a group of citizenship. At the same time, the Cherokee Supreme Court ordered a special run-off election to be held September 24, 2011 to settle the office of Principal Chief. Earlier voting in this year's election had been so close that the incumbent Chad Smith and challenger Bill John Baker, longtime Cherokee National Council member, had each twice been declared the winner. On September 11, the nation sent letters to Freedmen, notifying them of their loss of citizenship and voting rights. The US Department of Housing and Urban Development froze $33 million in funds to the Cherokee Nation while studying the case, pursuant to a stipulation in the 2008 congressional renewal of Self-Determination Act.
=== Seed dispersion and deterrents against granivorous mammals === Granivorous mammals pose a risk to the propagation of chilies because their molars grind the seeds of chilies, rendering them unable to grow into new chili plants. As a result, modern chilies evolved defense mechanisms to mitigate the risk of granivorous mammals. While capsaicin is present at some level in every part of the pepper, the chemical has its highest concentration in the tissue near the seeds within chilies. Birds are able to eat chilies, then disperse the seeds in their excrement, enabling propagation.
=== Holter monitor === A Holter monitor records a continuous EKG rhythm pattern (rarely a full EKG) for 24 hours or more. These monitors are used for suspected frequent rhythm abnormalities, especially ones the wearer may not recognize by symptoms. They are more expensive than event monitors.
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.