This is a working overview of TB-500, written for readers who want more than a one-paragraph summary but less than a textbook.
Reviewed 2026-08-01. Anything still debated is marked as such rather than presented as settled.
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.
Thymosin beta-4 itself is a natural peptide of 43 residues found in many cell types and body fluids. Its best-characterised function is binding and sequestering actin monomers, which influences cytoskeletal dynamics. The sequence most often associated with TB-500, LKKTETQ, corresponds to part of that actin-binding region. A different fragment, Ac-SDKP, is also derived from the same parent peptide and is studied in its own right, which is one reason discussions of thymosin fragments can become confusing. The two are structurally distinct and are not interchangeable.
Thymosin beta-4 was isolated from calf thymus in the early 1980s and later characterised as an abundant intracellular actin-sequestering protein. Interest in short synthetic fragments grew once the actin-binding motif had been mapped to the middle of the sequence. TB-500 came out of that line of work as a truncated analogue rather than a natural isolate, and it is now sold mainly to laboratories. Published studies on the fragment have been largely in vitro or in animal models, and controlled human trials remain sparse, so claims about effects in people rest on extrapolation.
Literature and online discussion often conflate TB-500 with full-length thymosin beta-4, even though the two differ in size and are not interchangeable in analytical terms. The fragment is produced by solid-phase peptide synthesis, and the product is a defined seven-residue chain rather than a biological extract. Because the term is a trade-style label, two vendors may supply materials of the same nominal sequence but different counter-ion content, purity, or water content. Comparisons across studies are therefore difficult unless the exact sequence and purity are reported.
TB-500 is a research peptide whose sequence matches residues 17 to 23 of thymosin beta-4, a 43-residue protein present in most mammalian cells. The chain is seven amino acids long, written as LKKTETQ, and is normally supplied with an acetyl group on the N-terminus. Suppliers list it as a lyophilised powder under the code name TB-500, and the same sequence appears elsewhere in catalogues as the thymosin beta-4 actin-binding fragment. The label is commercial rather than systematic, so no single authority fixes exactly what TB-500 denotes.
| Property | Value | Notes |
|---|---|---|
| Name type | Commercial trade name | Not a systematic chemical identifier |
| Parent peptide | Thymosin beta-4 | 43-residue natural peptide |
| Common fragment sequence | LKKTETQ | Maps to part of the actin-binding region |
| Molecular size class | Roughly 0.8-1.0 kDa | Depends on exact fragment and terminal modification |
| Regulatory status | Prohibited in sport | Grouped with peptide hormones in many frameworks |
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.
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.
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.
Published research on the intact protein is substantial, covering actin regulation, cell migration, and wound models. Research using the heptapeptide fragment specifically is far smaller, and much of the circulating material originates in supplier documentation rather than peer-reviewed reports. Where fragment studies do exist, they often employ different sequences, chain lengths, or terminal modifications, which complicates direct comparison across papers. Readers encountering claims about TB-500 should therefore separate evidence about thymosin beta-4 from evidence about the fragment itself.
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.
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.
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.
In combined mass spectra obtained by summing a large number of individual ion detection events, each peak is a histogram obtained by adding up counts in each individual bin. Because the recording of the individual ion arrival with TDC yields only a single time point, the TDC eliminates the fraction of peak width determined by a limited response time of both the MCP detector and preamplifier. This propagates into better mass resolution. Modern ultra-fast 10 GSample/sec analog-to-digital converters digitize the pulsed ion current from the MCP detector at discrete time intervals (100 picoseconds). Modern 8-bit or 10-bit 10 GHz ADC has much higher dynamic range than the TDC, which allows its usage in MALDI-TOF instruments with its high peak currents. To record fast analog signals from MCP detectors one is required to carefully match the impedance of the detector anode with the input circuitry of the ADC (preamplifier) to minimize the "ringing" effect. Mass resolution in mass spectra recorded with ultra-fast ADC can be improved by using small-pore (2-5 micron) MCP detectors with shorter response times.
=== Analogues === A notable analogue of SDMA is 4T-MMDA-2 (2-methoxy-4T-MDA), which was described by Alexander Shulgin in his book PiHKAL (Phenethylamines I Have Known and Loved). Other analogues of SDMA include SDA, MDMA, 5-MAPB, and 6-MAPBT, among others.
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Though these events served as inspiration for the field, the actual breakthrough in practical approaches to synthesize artificial molecular machines (AMMs) took place in 1991 with the invention of a "molecular shuttle" by Sir Fraser Stoddart. Building upon the assembly of mechanically linked molecules such as catenanes and rotaxanes as developed by Jean-Pierre Sauvage in the early 1980s, this shuttle features a rotaxane with a ring that can move across an "axle" between two ends or possible binding sites (hydroquinone units). This design realized the well-defined motion of a molecular unit across the length of the molecule for the first time. In 1994, an improved design allowed control over the motion of the ring by pH variation or electrochemical methods, making it the first example of an AMM. Here the two binding sites are a benzidine and a biphenol unit; the cationic ring typically prefers staying over the benzidine ring, but moves over to the biphenol group when the benzidine gets protonated at low pH or if it gets electrochemically oxidized. In 1998, a study could capture the rotary motion of a decacyclene molecule on a copper-base metallic surface using a scanning tunneling microscope. Over the following decade, a broad variety of AMMs responding to various stimuli were invented for different applications. In 2016, the Nobel Prize in Chemistry was awarded to Sauvage, Stoddart, and Bernard L. Feringa for the design and synthesis of molecular machines.
Sources: en.wikipedia.org
== Biological role == Dipicolinic acid composes 5% to 15% of the dry weight of Bacillus subtilis spores. It has been implicated as responsible for the heat resistance of the endospore, although mutants resistant to heat but lacking dipicolinic acid have been isolated, suggesting other mechanisms contributing to heat resistance are at work. Two genera of bacterial pathogens are known to produce endospores: the aerobic Bacillus and anaerobic Clostridium. Dipicolinic acid forms a complex with calcium ions within the endospore core. This complex binds free water molecules, causing dehydration of the spore. As a result, the heat resistance of macromolecules within the core increases. The calcium-dipicolinic acid complex also functions to protect DNA from heat denaturation by inserting itself between the nucleobases, thereby increasing the stability of DNA.
== Structure == Most RTKs are single subunit receptors but some exist as multimeric complexes, e.g., the insulin receptor that forms disulfide linked dimers in the presence of hormone (insulin); moreover, ligand binding to the extracellular domain induces formation of receptor dimers. Each monomer has a single hydrophobic transmembrane-spanning domain composed of 25 to 38 amino acids, an extracellular N terminal region, and an intracellular C terminal region. The extracellular N terminal region exhibits a variety of conserved elements including immunoglobulin (Ig)-like or epidermal growth factor (EGF)-like domains, fibronectin type III repeats, or cysteine-rich regions that are characteristic for each subfamily of RTKs; these domains contain primarily a ligand-binding site, which binds extracellular ligands, e.g., a particular growth factor or hormone. The intracellular C terminal region displays the highest level of conservation and comprises catalytic domains responsible for the kinase activity of these receptors, which catalyses receptor autophosphorylation and tyrosine phosphorylation of RTK substrates.
==== MeSH D13.695.827 – ribonucleotides ==== MeSH D13.695.827.068 – adenine nucleotides MeSH D13.695.827.068.124 – adenosine diphosphate MeSH D13.695.827.068.124.070 – adenosine diphosphate sugars MeSH D13.695.827.068.124.070.075 – adenosine diphosphate glucose MeSH D13.695.827.068.124.070.125 – adenosine diphosphate ribose MeSH D13.695.827.068.124.070.125.040 – o-acetyl-adp-ribose MeSH D13.695.827.068.124.070.125.195 – cyclic adp-ribose MeSH D13.695.827.068.180 – adenosine monophosphate MeSH D13.695.827.068.180.080 – adenosine phosphosulfate MeSH D13.695.827.068.236 – adenosine triphosphate MeSH D13.695.827.068.236.050 – adenylyl imidodiphosphate MeSH D13.695.827.068.236.250 – ethenoadenosine triphosphate MeSH D13.695.827.068.309 – clofarabine MeSH D13.695.827.068.382 – coenzyme a MeSH D13.695.827.068.382.300 – acyl coenzyme a MeSH D13.695.827.068.382.300.020 – acetyl coenzyme a MeSH D13.695.827.068.382.300.500 – malonyl coenzyme a MeSH D13.695.827.068.382.300.700 – palmitoyl coenzyme a MeSH D13.695.827.068.395 – cyclic amp MeSH D13.695.827.068.395.225 – 8-bromo cyclic adenosine monophosphate MeSH D13.695.827.068.395.250 – bucladesine MeSH D13.695.827.068.506 – flavin-adenine dinucleotide MeSH D13.695.827.068.694 – nad MeSH D13.695.827.068.749 – nadp MeSH D13.695.827.068.850 – phosphoadenosine phosphosulfate MeSH D13.695.827.232 – cytosine nucleotides MeSH D13.695.827.232.115 – cyclic cmp MeSH D13.695.827.232.150 – cytidine diphosphate MeSH D13.695.827.232.150.180 – cytidine diphosphate choline MeSH D13.695.827.232.150.210 – cytidine diphosphate diglycerides MeSH D13.695.827.232.370 – cytidine monophosphate MeSH D13.695.827.232.370.250 – cytidine monophosphate n-acetylneuraminic acid MeSH D13.695.827.232.400 – cytidine triphosphate MeSH D13.695.827.349 – flavin mononucleotide MeSH D13.695.827.426 – guanine nucleotides MeSH D13.695.827.426.160 – cyclic gmp MeSH D13.695.827.426.160.325 – dibutyryl cyclic gmp MeSH D13.695.827.426.340 – guanosine diphosphate MeSH D13.695.827.426.340.350 – guanosine diphosphate sugars MeSH D13.695.827.426.340.350.400 – guanosine diphosphate fucose MeSH D13.695.827.426.340.350.500 – guanosine diphosphate mannose MeSH D13.695.827.426.400 – guanosine monophosphate MeSH D13.695.827.426.440 – guanosine pentaphosphate MeSH D13.695.827.426.480 – guanosine tetraphosphate MeSH D13.695.827.426.504 – guanosine triphosphate MeSH D13.695.827.426.504.380 – guanosine 5'-o-(3-thiotriphosphate) MeSH D13.695.827.426.504.400 – guanylyl imidodiphosphate MeSH D13.695.827.426.700 – rna caps MeSH D13.695.827.426.700.710 – rna cap analogs MeSH D13.695.827.519 – inosine nucleotides MeSH D13.695.827.519.300 – cyclic imp MeSH D13.695.827.519.400 – inosine diphosphate MeSH D13.695.827.519.500 – inosine monophosphate MeSH D13.695.827.519.800 – inosine triphosphate MeSH D13.695.827.648 – nicotinamide mononucleotide MeSH D13.695.827.708 – nucleoside diphosphate sugars MeSH D13.695.827.708.070 – adenosine diphosphate sugars MeSH D13.695.827.708.070.075 – adenosine diphosphate glucose MeSH D13.695.827.708.070.125 – adenosine diphosphate ribose MeSH D13.695.827.708.070.125.040 – o-acetyl-adp-ribose MeSH D13.695.827.708.070.125.195 – cyclic adp-ribose MeSH D13.695.827.708.070.125.600 – poly adenosine diphosphate ribose MeSH D13.695.827.708.260 – cytidine diphosphate diglycerides MeSH D13.695.827.708.400 – guanosine diphosphate sugars MeSH D13.695.827.708.400.410 – guanosine diphosphate fucose MeSH D13.695.827.708.400.500 – guanosine diphosphate mannose MeSH D13.695.827.708.727 – uridine diphosphate sugars MeSH D13.695.827.708.727.100 – uridine diphosphate n-acetylgalactosamine MeSH D13.695.827.708.727.120 – uridine diphosphate n-acetylglucosamine MeSH D13.695.827.708.727.150 – uridine diphosphate n-acetylmuramic acid MeSH D13.695.827.708.727.300 – uridine diphosphate galactose MeSH D13.695.827.708.727.350 – uridine diphosphate glucose MeSH D13.695.827.708.727.375 – uridine diphosphate glucuronic acid MeSH D13.695.827.708.727.800 – uridine diphosphate xylose MeSH D13.695.827.919 – uracil nucleotides MeSH D13.695.827.919.600 – uridine diphosphate MeSH D13.695.827.919.600.677 – uridine diphosphate sugars MeSH D13.695.827.919.600.677.100 – uridine diphosphate n-acetylgalactosamine MeSH D13.695.827.919.600.677.120 – uridine diphosphate n-acetylglucosamine MeSH D13.695.827.919.600.677.150 – uridine diphosphate n-acetylmuramic acid MeSH D13.695.827.919.600.677.300 – uridine diphosphate galactose MeSH D13.695.827.919.600.677.350 – uridine diphosphate glucose MeSH D13.695.827.919.600.677.375 – uridine diphosphate glucuronic acid MeSH D13.695.827.919.600.677.800 – uridine diphosphate xylose MeSH D13.695.827.919.877 – uridine monophosphate MeSH D13.695.827.919.877.500 – sofosbuvir MeSH D13.695.827.919.950 – uridine triphosphate
From 1935–1972, the authorising body governing radiation in Australia was the Commonwealth X-Ray and Radium Laboratory. This was replaced by the Commonwealth Radiation Laboratory (1972–1973), and then the Australian Radiation Laboratory (1973–1999). In 1999, the Australian Radiation Laboratory then merged with the Nuclear Safety Bureau to create one agency that governed radiation and nuclear safety, ARPANSA. Since its establishment, ARPANSA has offices in both Sydney, NSW, and Melbourne, Victoria.
Electrolysis then gave calcium–mercury and magnesium–mercury amalgams, and distilling off the mercury gave the metal. However, pure calcium cannot be prepared in bulk by this method and a workable commercial process for its production was not found until over a century later.
Sources: en.wikipedia.org
Troglitazone was developed by Daiichi Sankyo (Japan). In the United States, it was introduced and manufactured by Parke-Davis in the late 1990s but turned out to be associated with an idiosyncratic reaction leading to drug-induced hepatitis. The Food and Drug Administration (FDA) medical officer assigned to evaluate troglitazone, John Gueriguian, did not recommend its approval due to potentially high liver toxicity; Parke-Davis complained to the FDA, and Gueriguian was subsequently removed from his post. A panel of experts approved it in January 1997. Once the prevalence of adverse liver effects became known, troglitazone was withdrawn from the British market in December 1997, from the United States market in 2000, and from the Japanese market soon afterwards. It did not get approval in the rest of Europe. Troglitazone was developed as the first anti-diabetic drug having a mechanism of action involving a decrease in insulin resistance. At the time, it was widely believed that such drugs, by addressing the primary metabolic defect associated with Type 2 diabetes, would have numerous benefits including avoiding the risk of hypoglycemia associated with insulin and earlier oral antidiabetic drugs. It was further believed that reducing insulin resistance would potentially reduce the very high rate of cardiovascular disease that is associated with diabetes. Parke-Davis/Warner Lambert submitted the diabetes drug Rezulin for FDA review on July 31, 1996. The medical officer assigned to the review, Dr. John L.
==== Cationic head groups ==== Cationic surfactants are extensively described in this review. pH-dependent primary, secondary, or tertiary amines; primary and secondary amines become positively charged at pH < 10: octenidine dihydrochloride. Permanently charged quaternary ammonium salts: cetrimonium bromide (CTAB), cetylpyridinium chloride (CPC), benzalkonium chloride (BAC), benzethonium chloride (BZT), dimethyldioctadecylammonium chloride, and dioctadecyldimethylammonium bromide (DODAB).
For small strains, the measure of stress that is used is the Cauchy stress while the measure of strain that is used is the infinitesimal strain tensor; the resulting (predicted) material behavior is termed linear elasticity, which (for isotropic media) is called the generalized Hooke's law. Cauchy elastic materials and hypoelastic materials are models that extend Hooke's law to allow for the possibility of large rotations, large distortions, and intrinsic or induced anisotropy. For more general situations, any of a number of stress measures can be used, and it is generally desired (but not required) that the elastic stress–strain relation be phrased in terms of a finite strain measure that is work conjugate to the selected stress measure, i.e., the time integral of the inner product of the stress measure with the rate of the strain measure should be equal to the change in internal energy for any adiabatic process that remains below the elastic limit.
=== Permian reptiles === With the close of the Carboniferous, the amniotes became the dominant tetrapod fauna. While primitive, terrestrial reptiliomorphs still existed, the synapsid amniotes evolved the first truly terrestrial megafauna (giant animals) in the form of pelycosaurs, such as Edaphosaurus and the carnivorous Dimetrodon. In the mid-Permian period, the climate became drier, resulting in a change of fauna: The pelycosaurs were replaced by the therapsids. Many stem reptile groups continued to flourish throughout the Permian. The herbivorous pareiasaurs were the first lineage of reptiles to reach a large body size, with the largest representatives of the group having a body mass estimated to exceed 1,000 kilograms (2,200 lb). One of the best known early stem-reptiles is Mesosaurus, a genus from the Early Permian of Southern Africa and South America that had returned to water and gained webbed feet, feeding on crustaceans in marine or lagoonal environments. The earliest true diapsids (Neodiapsida), such as Youngina, appeared during the Middle-Late Permian. The Weigeltisauridae, a group of diapsids from the Late Permian, are the oldest known tetrapods to have engaged in flight, using novel rod-like bones extending from the trunk which formed wings to glide between trees.
Sources: en.wikipedia.org
No. Thymosin beta-4 is a 43-residue natural peptide, while TB-500 is a commercial label applied to a short synthetic fragment of it. The two differ in length, sequence coverage and how they are handled in the laboratory.
Published work usually examines actin binding, cell migration and tissue repair endpoints in cell and animal models. Findings are generally described as preliminary, and controlled human data remain limited.
Because TB-500 is a trade name rather than a chemical identifier, different vendors and papers may attach it to different fragment lengths. Checking the stated sequence is the practical way to resolve the ambiguity.
No. Thymosin beta-4 is a 43-residue protein, while TB-500 matches only residues 17 to 23 of that chain. The two are related but differ in size, and a method that identifies one does not automatically identify the other.