TB-500 is one of those subjects where the details matter more than the headlines. This page pulls together the background, the mechanisms, and the practical points readers ask about most.
Last reviewed on 2025-09-02. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
Dry powder is commonly held at minus twenty degrees Celsius, with some suppliers recommending lower temperatures for long-term archival storage. Once dissolved, solutions are typically kept cold and protected from light, since aqueous peptide solutions can lose integrity through hydrolysis or oxidation over time. Stability data specific to this fragment are limited in the public literature, and much of the guidance comes from general peptide handling practice rather than from controlled degradation studies. Users therefore treat stated shelf lives as approximate rather than fixed.
Identity and purity are normally assessed with reversed-phase high-performance liquid chromatography, paired with mass spectrometry to confirm molecular mass. A certificate of analysis reports a purity percentage, usually derived from chromatographic peak area, but that figure does not by itself prove a correct sequence or the absence of counterions. Independent verification may include amino acid analysis or peptide mapping. Batch-to-batch variation is a documented concern in the research chemical market, and the gap between a quoted purity value and actual peptide content can be substantial when the material is a salt or retains residual water.
Lyophilized peptide arrives as a dry cake that should stay sealed until use. Reconstitution is generally performed with sterile water or a buffered solution, and the resulting liquid should be handled gently to limit mechanical stress. Repeated freeze-thaw cycles are widely described as harmful to short peptides, so dividing a reconstituted batch into single-use portions is a common practice. Laboratories also record the solvent, concentration, and date of preparation on the vial label to keep later measurements traceable.
| 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 |
TB-500 is a synthetic seven-amino-acid peptide with the sequence LKKTETQ, corresponding to residues 17 through 23 of the protein thymosin beta-4. The N-terminus is typically acetylated in the described form, giving a monoisotopic mass near 888.5 Da and an average mass of about 889 Da. The designation TB-500 is a catalogue label rather than a formal chemical name, and the same sequence appears in the literature under several alternative abbreviations. It is handled as a research reagent rather than a pharmaceutical product.
Thymosin beta-4 is a 43-residue actin-binding protein found in most mammalian cell types, where it participates in cytoskeletal regulation and cell migration. TB-500 represents only a short fragment of that protein and does not include the remaining residues. Whether the isolated fragment reproduces the full range of activities reported for the intact protein remains an open question. Researchers commonly treat the two as related but distinct entities when comparing results.
Published work involving this sequence spans actin-binding assays, cell-migration studies, wound-healing models, and cardiovascular or musculoskeletal experiments. Much of the biological rationale derives from in vitro systems and animal models, and the number of controlled human studies is small. Reported outcomes vary across preparations, doses, and routes, which complicates comparison between studies. Reviews generally describe the evidence base as preliminary rather than settled. Mechanistic explanations are often proposed by analogy to the parent protein rather than demonstrated directly.
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.
Research interest in thymosin beta-4 fragments centres on actin sequestration, cell migration and tissue repair models. Most published work uses cultured cells or animal wound and cardiac preparations, and findings are generally described as preliminary. No fragment of this protein has been approved as a therapeutic product by major regulators. Reviews of the field note inconsistent dosing, delivery routes and outcome measures across studies, which complicates direct comparison. The material is best understood as a laboratory reagent with an active but unresolved research literature.
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.
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.
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.
linker DNA 1. A short, synthetic DNA duplex containing the recognition sequence for a particular restriction enzyme. In molecular cloning, linkers are often deliberately included in recombinant molecules in order to make them easily modifiable by permitting cleavage and insertion of foreign sequences at precise locations. A segment of an engineered plasmid containing many such restriction sites is sometimes called a polylinker. 2. A section of chromosomal DNA connecting adjacent nucleosomes by binding to histone H1.
Also, because the acid is denser than water, it sinks to the bottom. Heat is generated at the interface between acid and water, which is at the bottom of the vessel. Acid will not boil, because of its higher boiling point. Warm water near the interface rises due to convection, which cools the interface, and prevents boiling of either acid or water. In contrast, addition of water to concentrated sulfuric acid results in a thin layer of water on top of the acid. Heat generated in this thin layer of water can boil, leading to the dispersal of a sulfuric acid aerosol, or worse, an explosion. Preparation of solutions greater than 6 M (35%) in concentration is dangerous, unless the acid is added slowly enough to allow the mixture sufficient time to cool. Otherwise, the heat produced may be sufficient to boil the mixture. Efficient mechanical stirring and external cooling (such as an ice bath) are essential. Reaction rates double for about every 10-degree Celsius increase in temperature. Therefore, the reaction will become more violent as dilution proceeds, unless the mixture is given time to cool. Adding acid to warm water will cause a violent reaction. On a laboratory scale, sulfuric acid can be diluted by pouring concentrated acid onto crushed ice made from de-ionized water. The ice melts in an endothermic process while diluting the acid. The amount of heat needed to melt the ice in this process is greater than the amount of heat evolved by diluting the acid so the solution remains cold. After all the ice has melted, further dilution can take place using water.
Cytokinins are a class of plant hormones named for their control of cell division (especially cytokinesis). The natural cytokinin zeatin was discovered in corn, Zea mays, and is a derivative of the purine adenine. Zeatin is produced in roots and transported to shoots in the xylem where it promotes cell division, bud development, and the greening of chloroplasts. The gibberelins, such as gibberelic acid are diterpenes synthesised from acetyl CoA via the mevalonate pathway. They are involved in the promotion of germination and dormancy-breaking in seeds, in regulation of plant height by controlling stem elongation and the control of flowering. Abscisic acid (ABA) occurs in all land plants except liverworts, and is synthesised from carotenoids in the chloroplasts and other plastids. It inhibits cell division, promotes seed maturation, and dormancy, and promotes stomatal closure. It was so named because it was originally thought to control abscission. Ethylene is a gaseous hormone that is produced in all higher plant tissues from methionine. It is now known to be the hormone that stimulates or regulates fruit ripening and abscission, and it, or the synthetic growth regulator ethephon which is rapidly metabolised to produce ethylene, are used on industrial scale to promote ripening of cotton, pineapples and other climacteric crops.
== Structure == Human chorionic gonadotropin is a glycoprotein composed of 237 amino acids with a molecular mass of 36.7 kDa, approximately 14.5kDa αhCG and 22.2kDa βhCG. It is heterodimeric, with an α (alpha) subunit identical to that of luteinizing hormone (LH), follicle-stimulating hormone (FSH), thyroid-stimulating hormone (TSH), and a β (beta) subunit that is unique to hCG.
Sources: en.wikipedia.org
Icaridin (Insect repellent) SSRIs (selective serotonin reuptake inhibitors) Paroxetine Stimulants and nootropics: Methylphenidate Ethylphenidate Pipradrol Desoxypipradrol Histamine 1 (H1) receptor antagonists/inverse agonists: Loratadine Histamine 3 (H3) receptor antagonists/inverse agonists: Pitolisant SERM (selective estrogen receptor modulators) Raloxifene Vasodilators Minoxidil Antipsychotic medications: Droperidol Haloperidol Melperone Mesoridazine Risperidone Thioridazine Opioids: Dipipanone Fentanyl and analogs Loperamide Pethidine (meperidine) Prodine Arylcyclohexylamines: PCP and analogs anticholinergic chemical weapons Ditran N-Methyl-3-piperidyl benzilate (JB-336, BZ) Piperidine is also commonly used in chemical degradation reactions, such as the sequencing of DNA in the cleavage of particular modified nucleotides. Piperidine is also commonly used as a base for the deprotection of Fmoc-amino acids used in solid-phase peptide synthesis. Piperidine is listed as a Table II precursor under the United Nations Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances due to its use (peaking in the 1970s) in the clandestine manufacture of phencyclidine.
Secondary ion mass spectrometry (SIMS) is used to analyze the composition of solid surfaces and thin films by sputtering the surface of the specimen with a focused primary ion beam and collecting and analyzing ejected secondary ions. The mass/charge ratios of these secondary ions are measured with a mass spectrometer to determine the elemental, isotopic, or molecular composition of the surface to a depth of 1 to 2 nm. In a liquid metal ion source (LMIS), a metal (typically gallium) is heated to the liquid state and provided at the end of a capillary or a needle. Then a Taylor cone is formed under the application of a strong electric field. As the cone's tip get sharper, the electric field becomes stronger, until ions are produced by field evaporation. These ion sources are particularly used in ion implantation or in focused ion beam instruments.
October 5–10, 1908 - The rapidly growing, global industry and scientific quest for absolute zero led to the 1st International Congress of Refrigeration held in Paris, France, at the Paris-Sorbonne University, which welcomed over 5,000 participants. January 25, 1909 - From this first Congress, the International Association of Refrigeration was born, formed by delegates from 35 countries. June 21, 1920 - The association was reorganised and officially titled as the International Institute of Refrigeration – IIR (Institut International du Froid – IIF, in French). IIR's status as an international organisation was defined by an International Agreement signed on December 1, 1954, and General Regulations for the Application of the International Agreements signed on November 20, 1956. Since then, the IIR has been operating at its headquarters based in Paris and is now an international organisation for expertise on refrigeration. The institute has continued to run the International Congress of Refrigeration every four years since its inauguration and has now expanded its event portfolio to ten conference series covering a wide variety of refrigeration topics. Working alongside governments, today the IIR remains committed to promoting knowledge on refrigeration for sustainable development, and continues to provide key services to disseminate information on associated technologies to all stakeholders (companies, universities, professionals, etc.).
Sources: en.wikipedia.org
=== Oxygen carriers === Hemoglobin, which is the principal oxygen-carrier in humans, has four subunits in which the iron(II) ion is coordinated by the planar macrocyclic ligand protoporphyrin IX (PIX) and the imidazole nitrogen atom of a histidine residue. The sixth coordination site contains a water molecule or a dioxygen molecule. By contrast the protein myoglobin, found in muscle cells, has only one such unit. The active site is located in a hydrophobic pocket. This is important as without it the iron(II) would be irreversibly oxidized to iron(III). The equilibrium constant for the formation of HbO2 is such that oxygen is taken up or released depending on the partial pressure of oxygen in the lungs or in muscle. In hemoglobin the four subunits show a cooperativity effect that allows for easy oxygen transfer from hemoglobin to myoglobin. In both hemoglobin and myoglobin it is sometimes incorrectly stated that the oxygenated species contains iron(III). It is now known that the diamagnetic nature of these species is because the iron(II) atom is in the low-spin state. In oxyhemoglobin the iron atom is located in the plane of the porphyrin ring, but in the paramagnetic deoxyhemoglobin the iron atom lies above the plane of the ring. This change in spin state is a cooperative effect due to the higher crystal field splitting and smaller ionic radius of Fe2+ in the oxyhemoglobin moiety. Hemerythrin is another iron-containing oxygen carrier. The oxygen binding site is a binuclear iron center.
In order to stop white emigration, the Smith government brought in a law in 1975 forbidding Rhodesian citizens from holding foreign currency, but the law was widely flouted. In order to encourage white emigration, the guerrillas of ZANU and ZAPU followed a strategy of attacking anything and everything that was of economic value across the country in order to force the state to call up more men, and of killing white civilians. Killing Rhodesian white citizens tended to have an "echo effect" as the ZANU and ZAPU had each estimated that for one white citizen killed, it caused about 20 to leave Rhodesia.
==== MeSH D12.776.422.220.453 – cytochrome p-450 enzyme system ==== MeSH D12.776.422.220.453.040 – aryl hydrocarbon hydroxylases MeSH D12.776.422.220.453.040.050 – aniline hydroxylase MeSH D12.776.422.220.453.040.110 – benzopyrene hydroxylase MeSH D12.776.422.220.453.040.332 – cytochrome p-450 cyp1a1 MeSH D12.776.422.220.453.040.555 – cytochrome p-450 cyp1a2 MeSH D12.776.422.220.453.040.777 – cytochrome p-450 cyp2b1 MeSH D12.776.422.220.453.040.888 – cytochrome p-450 cyp2d6 MeSH D12.776.422.220.453.040.944 – cytochrome p-450 cyp2e1 MeSH D12.776.422.220.453.040.972 – cytochrome p-450 cyp3a MeSH D12.776.422.220.453.085 – camphor 5-monooxygenase MeSH D12.776.422.220.453.915 – steroid hydroxylases MeSH D12.776.422.220.453.915.050 – aldosterone synthase MeSH D12.776.422.220.453.915.099 – aromatase MeSH D12.776.422.220.453.915.200 – cholesterol 7 alpha-hydroxylase MeSH D12.776.422.220.453.915.212 – cholesterol side-chain cleavage enzyme MeSH D12.776.422.220.453.915.400 – 25-hydroxyvitamin d3 1-alpha-hydroxylase MeSH D12.776.422.220.453.915.720 – steroid 11-beta-hydroxylase MeSH D12.776.422.220.453.915.730 – steroid 12-alpha-hydroxylase MeSH D12.776.422.220.453.915.737 – steroid 16-alpha-hydroxylase MeSH D12.776.422.220.453.915.748 – steroid 17-alpha-hydroxylase MeSH D12.776.422.220.453.915.760 – steroid 21-hydroxylase
=== Economics === In the United States, the 800 mcg tablet was 6.75 times more expensive as of 2020 than the lozenge. As of 2023, the average cost for an injectable fentanyl solution (50 mcg/mL) is around US$17 for a supply of 20 milliliters, depending on the pharmacy. In a 2020 report by the Australian Institute of Criminology, a 100-microgram transdermal patch was valued from between AU$75 and AU$450 on illicit markets. Furthermore, in another 2020 study, the average price per gram of non-pharmaceutical fentanyl on various cryptomarkets was US$1,470.40 for offerings of less than five grams; the average for offers over five grams was US$139.50. In addition, on DreamMarket furanfentanyl (Fu-F), the most common analog on said market, the average price per gram was US$243.10 for retail listings and US$26.50 per gram for wholesale listings.
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.
Dry lyophilized powder is usually kept frozen, desiccated, and out of direct light. Sealed vials are not opened until needed, because moisture uptake can degrade short peptides. Longer archival storage is often done at lower temperatures than routine working stock.