The short version of Ac-LKKTETQ fits in a sentence. The long version — which is the one that helps — is below.
This page was last updated on 2025-08-17 and is reviewed periodically as new material appears.
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.
Thymosin beta-4 contains 43 amino acids and has a reported molecular mass near 4963 Da. The short fragment most often associated with the TB-500 label, an acetylated chain beginning LKKTETQ, has a reported mass near 889 Da, so the two are easily separated in analytical work. Mass spectrometry and amino acid analysis can confirm which material is present in a given sample. Statements treating TB-500 and thymosin beta-4 as interchangeable are therefore imprecise, even though the two appear together in much of the same literature.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Physical form | Lyophilised powder | Sealed vial; reconstituted before laboratory use |
| Appearance | White to off-white solid | Visual descriptor used on certificates of analysis |
| Solubility class | Water-soluble | Dissolves in water and aqueous buffers |
| Reported mass, fragment | Near 889 Da | Value depends on the stated sequence |
| Reported mass, parent protein | Near 4963 Da | 43-residue thymosin beta-4 |
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.
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.
Identity and purity are usually assessed by reversed-phase high-performance liquid chromatography together with mass spectrometry. The chromatogram provides a purity estimate as a percentage of total peak area, while the mass spectrum confirms that the observed mass matches the expected value. Amino acid analysis or tandem mass spectrometry sequencing can provide additional confirmation. Reported purity figures depend on the column, gradient, and detection wavelength, so values from different laboratories are not directly comparable without method details.
Lyophilised peptide is normally reconstituted with sterile water or a neutral buffer shortly before use. Because repeated freeze-thaw cycles can degrade the material, dividing a reconstituted solution into single-use aliquots is a common practice. Working solutions are usually kept cold and protected from light. The exact shelf life depends on concentration, buffer composition, and handling, so it is often determined empirically rather than assumed.
Peptide bonds are susceptible to hydrolysis under extreme pH and to enzymatic cleavage if proteases are present. Heat, oxidising agents, and prolonged exposure to light also contribute to loss of material. Aggregation can occur at high concentrations or in certain buffer systems, and it may not be visible to the eye. Storage at -20 C or below is typical for both powder and aliquoted solutions, and desiccation of the powder is preferred.
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.
The designation TB-500 circulates in laboratory and catalog contexts without a single agreed definition. Most product listings apply it to an N-terminally acetylated seven-residue fragment of thymosin beta-4, while other listings attach the same label to the full 43-residue protein. Because the term is commercial rather than systematic, two entries bearing identical names may describe different molecules. Any documentation should therefore state which sequence a given sample is claimed to contain.
The fragment most often associated with the name carries the sequence Ac-LKKTETQ, matching residues 17 through 23 of thymosin beta-4. That region holds the actin-binding motif responsible for much of the parent protein's biochemical activity. Apart from N-terminal acetylation the peptide is unmodified and contains no disulfide bonds, so it shows little ordered secondary structure in solution. Full-length thymosin beta-4 is instead a 43-residue polypeptide of roughly 4.9 kDa found widely across mammalian cell types.
=== Loss of solubility === When proteins are folded, they fold so as to keep their hydrophobic parts on the inside (away from water) and their hydrophilic parts on the outside (contacting the water). This makes them soluble enough not to precipitate. However, when denatured the surface of the protein is partly hydrophobic and partly hydrophilic (as it no longer has an "inside" in which to hide the hydrophobic parts), causing it to become insoluble in water. The hydrophobic parts of the denatured proteins stick together, forming a network (gel): this is called coagulation. The coagulation of denatured proteins is the reason eggs solidify when cooked. When acid is added to milk, the protein casein denatures and coagulates (with fat and water inclusions from the milk) into curds, the first step in making cheese; although milk can also be made to curdle (i.e. casein to coagulate) by other methods, for example the addition of enzymes like chymosin.
== Development == The vitreous fluid is not present at birth (the eye being filled with only the gel-like vitreous body), but found after age 4–5, and increases in size thereafter. Produced by cells in the non-pigmented portion of the ciliary body, the vitreous humour is derived from embryonic mesenchyme cells, which degenerate after birth. The nature and composition of the vitreous humour changes over the course of life. In adolescence, the vitreous cortex becomes more dense and vitreous tracts develop; and in adulthood, the tracts become better defined and sinuous. Central vitreous liquefies, fibrillar degeneration occurs, and the tracts break up (syneresis). Coarse strands develop with ageing. The gel volume decreases with age, and the liquid volume increases. The cortex may disappear at sites, allowing liquid vitreous to extrude adjacently into the potential space between vitreous cortex and retina (vitreous detachment).
=== 21st century === Rates of scurvy in the developed world are low due to the greater access to vitamin C-rich foods. Those most commonly affected are malnourished people in the developing world and homeless people. There have been outbreaks of the condition in refugee camps. Case reports in the developing world of those with poorly healing wounds have occurred. In 2020, the overall incidence of scurvy in the US was about one in 4,000 people, up significantly from even a few years before. About two-thirds of all scurvy is found in autistic people. Children and young people with autism are at risk of developing scurvy because some of them only eat a small number of foods (e.g., only rice and pasta). For some of them, the restricted diet takes the form of avoidant/restrictive food intake disorder (ARFID).
Sources: en.wikipedia.org
Chlorpropamide and other sulfonylureas encourage weight gain, so they are generally not favored for use in very obese patients. Metformin (Glucophage) is considered a better drug for these patients. Sulfonylureas should be used with caution or generally avoided in patients with hepatic and renal impairment, patients with porphyria, patients who are breastfeeding, patients with ketoacidosis, and elderly patients.
ATP + NH3 + CO2 ⇌ ADP + H2N−C(=O)−O−PO2−3 An important example of an enzyme with this activity is carbamoyl phosphate synthetase, e.g. carbamoyl phosphate synthetase I carrying out the first step of the urea cycle in order to dispose of waste ammonia. One hemoglobin molecule can carry four molecules of carbon dioxide to the lungs as carbamate groups formed by reaction of CO2 with four terminal amine groups of the deoxy form. The resulting compound is called carbaminohaemoglobin.
In the nonoverlapping triangles APB, BPC, CPD, DPA formed by the diagonals in a convex quadrilateral ABCD, where the diagonals intersect at P, there are the following characterizations of tangential quadrilaterals. Let r1, r2, r3, and r4 denote the radii of the incircles in the four triangles APB, BPC, CPD, and DPA respectively. Chao and Simeonov proved that the quadrilateral is tangential if and only if
CR665 (H-D-Phe-D-Phe-D-Nle-D-Arg-NH-4-Picolyl), also known by the previous developmental code names FE-200665 and JNJ-38488502, is an all D-amino acid peptide that acts as a peripherally restricted κ-opioid receptor agonist. The selectivity for FE 200665 is 1/16,900/84,600 for the human κ, μ, and δ opioid receptors, respectively. The dose of FE 200665 required to produce motor impairment (measure of CNS penetration) was 548 times higher than the dose required for antinociceptive activity. It is being developed for use by Cara Therapeutics under the code name CR665. A small, blinded study was done in healthy humans to determine the analgesic effects. CR665 was dosed at 0.36 mg/kg I.V., and was compared to 15 mg oxycodone orally. CR665 had analgesic effects on visceral pain, but produced a hyperalgesic response in a skin pinch test.
Sources: en.wikipedia.org
== Evolution == Based on parsimony-based phylogenetic analysis, the most recent common ancestor of all eukaryotes most likely already possessed an early RNAi pathway; the absence of the pathway in certain eukaryotes is thought to be a derived characteristic. This ancestral RNAi system probably contained at least one Dicer-like protein, one Argonaute, one PIWI protein, and an RNA-dependent RNA polymerase that may also have played other cellular roles. A large-scale comparative genomics study likewise indicates that the eukaryotic crown group already possessed these components, which may then have had closer functional associations with generalized RNA degradation systems such as the exosome. This study also suggests that the RNA-binding Argonaute protein family, which is shared among eukaryotes, most archaea, and at least some bacteria (such as Aquifex aeolicus), is homologous to and originally evolved from components of the translation initiation system.
Reprocessing allows the recycling of the uranium and plutonium into fresh fuel (RepU and MOX) and a strong reduction of volume, decay heat and radiotoxicity of the HLW. A measure of the HLW hazard is provided by radiotoxicity coming from the different nature of radionuclides. The SNF radiotoxicity is usually evaluated as a function of time and compared to the natural uranium ore. The spent nuclear fuel without reprocessing has a long-term toxicity that is mainly dominated by transuranic elements. Mainly due to plutonium, SNF without reprocessing reaches the reference radiotoxicity level after about 300,000 years. After uranium and plutonium removal, HLW is less radioactive and it decays to the reference level within 10,000 years. Since minor actinides (MAs) also contribute to the long-term decay heat and radiotoxicity of the spent fuel, an advanced reprocessing could further reduce the radiotoxic inventory with a decay to the reference level of about 300 years.
Prior to Mendel, Imre Festetics, a Hungarian noble, who lived in Kőszeg before Mendel, was the first who used the word "genetic" in hereditarian context, and is considered the first geneticist. He described several rules of biological inheritance in his work The genetic laws of nature (Die genetischen Gesetze der Natur, 1819). His second law is the same as that which Mendel published. In his third law, he developed the basic principles of mutation (he can be considered a forerunner of Hugo de Vries). Festetics argued that changes observed in the generation of farm animals, plants, and humans are the result of scientific laws. Festetics empirically deduced that organisms inherit their characteristics, not acquire them. He recognized recessive traits and inherent variation by postulating that traits of past generations could reappear later, and organisms could produce progeny with different attributes. These observations represent an important prelude to Mendel's theory of particulate inheritance insofar as it features a transition of heredity from its status as myth to that of a scientific discipline, by providing a fundamental theoretical basis for genetics in the twentieth century.
Established uitlanders, including the mining magnates, wanted political, social, and economic control over their lives. These rights included a stable constitution, a fair franchise law, an independent judiciary and a better educational system. The Boers recognised that the more concessions they made to the uitlanders the greater the likelihood—with approximately 30,000 white male Boer voters and potentially 60,000 white male uitlanders—that their independent control of the Transvaal would be lost, and the territory absorbed into the British Empire. The uitlanders resented the taxes levied by the Transvaal government, particularly when this was not spent on Johannesburg or uitlander interests but diverted to projects elsewhere in the Transvaal. For example, as the gold-bearing ore sloped away from the outcrop underground to the south, more and more blasting was necessary to extract it, and mines consumed vast quantities of explosives. A box of dynamite costing five pounds included five shillings tax. Not only was this tax perceived as exorbitant, but British interests were offended when President Paul Kruger gave monopoly rights for the manufacture of the explosive to a non-British branch of the Nobel company, which infuriated Britain. The so-called "dynamite monopoly" became a casus belli. British imperial interests were alarmed when in 1894–95 Kruger proposed building a railway through Portuguese East Africa to Delagoa Bay, bypassing British-controlled ports in Natal and Cape Town and avoiding British tariffs.
Similar to plant cells, the cell wall of some microorganisms such as algae and yeast contains indigestible components, such as cellulose. The cells of some kind of SCP should be broken up in order to liberate the cell interior and allow complete digestion. Some kind of SCP exhibits unpleasant color and flavors. Depending on the kind of SCP and the cultivation conditions, care must be taken to prevent and control contamination by other microorganisms because contaminants may produce toxins such as mycotoxins or cyanotoxins. An interesting approach to address this problem was proposed with the fungus Scytalidium acidophilum which grows at a pH as low as 1, outside the tolerance of most microorganisms. This allows it to grow on acid-hydrolysed paper waste at low-cost. Some yeast and fungal proteins are deficient in methionine.
Sources: en.wikipedia.org
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.
Naming for research peptides is not standardised, and suppliers sometimes apply the same label to different chain lengths. Certificates of analysis and mass data are the practical way to determine what a given lot contains.
The fragment commonly cited under this label is reported near 889 Da, and the parent protein near 4963 Da. Reported values shift with the exact sequence and with residual counter-ions or water in the sample.
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.