This is a working overview of actin-binding motif, written for readers who want more than a one-paragraph summary but less than a textbook.
Reviewed 2026-07-01. Anything still debated is marked as such rather than presented as settled.
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.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Molecular formula | C38H68N10O14 | Acetylated heptapeptide form |
| Monoisotopic mass | 888.5 Da | Average mass about 889 Da |
| Appearance | White to off-white solid | Usually supplied as lyophilised powder |
| Solubility class | Highly water soluble | Also dissolves in aqueous buffers |
| Common synonyms | Tbeta4 fragment, thymosin beta-4 (17-23) | Refer to the same sequence |
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.
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.
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.
Lyophilised peptide powders are hygroscopic, and the fragment absorbs atmospheric moisture when a vial is opened at room temperature. Weighing and aliquoting are normally done quickly in a dry environment, and stock solutions are divided into single-use portions before freezing. Repeated freeze-thaw cycles are avoided because they promote aggregation and can shift the measured content of a vial. These practices are general to synthetic peptides rather than unique to this sequence, but they matter more for short chains kept for long periods.
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.
The compound circulates in the literature as a research reagent rather than an approved therapeutic. Regulatory agencies in several countries have not authorized it for medical use, and sporting bodies list related thymosin beta-4 peptides among prohibited substances. Suppliers typically market it with a purity figure and a certificate of analysis, while peer-reviewed clinical reports remain sparse. Discussions therefore often separate laboratory findings from anecdotal reports, and reviewers tend to note the small size and methodological limits of the available studies.
TB-500 refers to a synthetic peptide fragment derived from the actin-binding region of thymosin beta-4, a protein present in most mammalian cells. The full protein contains forty-three amino acids, while the commonly sold fragment is a much shorter acetylated sequence, often cited as LKKTETQ. The fragment retains part of the actin-binding motif but lacks the remainder of the parent protein. Material sold under this name is usually lyophilized powder intended for laboratory research, and it is not a finished pharmaceutical product.
Polish refugees were housed at dedicated settlements set up at Marandellas and Rusape, two towns about 40 km (25 mi) apart to the south-east of Salisbury, from 1943. There were similar camps in Kenya, Nyasaland, Tanganyika, Northern Rhodesia and South Africa. The Polish settlements in Southern Rhodesia were run jointly by local authorities and the Polish consulate in Salisbury; the Polish government-in-exile in London provided funding. Transport back to Europe picked up sharply as the war came to a close, and by October 1945 less than 2,000 Polish refugees remained. Colonial officials were reluctant to let the Poles stay indefinitely, asserting that they were not culturally British enough and might have communist connections or sympathies, but most of those who remained showed little inclination to leave. Southern Rhodesia ultimately allowed around 726 Polish refugees to settle permanently after the war.
==== Units ==== Due to the variety of natural and synthetic compounds with vitamin E activity, there has historically been many different units that attempt to produce a measure of "vitamin E activity" using a weighted sum. The international unit measurement was used by the United States in 1968–2016. 1 IU is the biological equivalent of about 0.667 mg d (RRR)-alpha-tocopherol (2/3 mg exactly), or of 0.90 mg of dl-alpha-tocopherol (or of 1.0 mg of dl-alpha-tocopherol acetate), corresponding to the then-measured relative potency of stereoisomers. In May 2016, the measurements were revised, such that 1 mg "as alpha-tocopherol" of Vitamin E is 1 mg of d-alpha-tocopherol or 2 mg of dl-alpha-tocopherol. The change was originally started in 2000, when forms of vitamin E other than alpha-tocopherol were dropped from dietary calculations by the IOM. The UL amount disregards any conversion. The EFSA has never used an IU unit, and their measurement only considers RRR-alpha-tocopherol.
=== Microscopy and imaging === An infrared microscope allows samples to be observed and spectra measured from regions as small as 5 microns across. Images can be generated by combining a microscope with linear or 2-D array detectors. The spatial resolution can approach 5 microns with tens of thousands of pixels. The images contain a spectrum for each pixel and can be viewed as maps showing the intensity at any wavelength or combination of wavelengths. This allows the distribution of different chemical species within the sample to be seen. This technique has been applied in various biological applications including the analysis of tissue sections as an alternative to conventional histopathology, examining the homogeneity of pharmaceutical tablets, and for differentiating morphologically-similar pollen grains.
Sources: en.wikipedia.org
=== Cancer === In response to a report of precancerous changes in the pancreases of rats and organ donors treated with the DPP-4 inhibitor sitagliptin, the US FDA and the European Medicines Agency each undertook independent reviews of all clinical and preclinical data related to the possible association of DPP-4 inhibitors with pancreatic cancer. In a joint letter to the New England Journal of Medicine, the agencies stated that they had not yet reached a final conclusion regarding a possible causative relationship. A 2014 meta-analysis found no evidence for increased pancreatic cancer risk in people treated with DPP-4 inhibitors, but owing to the modest amount of data available, the authors were unable to completely exclude possibly increased risk.
== Production == Produced mainly in parts of the world where pineapples are grown, such as Thailand or Malaysia, bromelain is extracted from the peel, stem, leaves or waste of the pineapple plant after processing the fruit for juice or other purposes. The starting material is blended and pressed through a filter to obtain a supernatant liquid containing the soluble bromelain enzyme. Further processing includes purification and concentration of the enzyme.
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== Work == The new São Paulo Institute was built in a section of the city named Butantan, at the time a far-away place, near the Pinheiros river, a swampy, sparsely inhabited area. Under Vital Brazil, it soon became an energetic and exemplary research center in vaccines and sera of all kinds, which were produced locally for the prophylaxis and treatment of tetanus, diphtheria, yellow fever, smallpox and several zoonoses (diseases transmitted to humans by animals), such as the dreaded hydrophobia. The Institute came to be well known by his original name, the Butantan Institute, and is still active today. Vital Brazil was convinced since his early work at Butantan that envenomations (poisoning by accidents with venomous animals, such as snakes, scorpions, spiders and batrachia, then the cause of thousands of deaths in Brazil) could be fought with antisera, i.e., antibodies specifically produced for venoms which were proteins or long-chain peptides. A French immunologist, Albert Calmette (1863–1933) had demonstrated this for the first time in 1892, by developing a monovalent serum to treat bites by the Indian cobra (Naja tripudians).
Sources: en.wikipedia.org
No. TB-500 is a short synthetic peptide matching residues 17 to 23 of thymosin beta-4, while the parent protein contains 43 residues. The fragment lacks the rest of the protein sequence, so the two are related but not identical.
It consists of leucine, lysine, lysine, threonine, glutamic acid, threonine, and glutamine in that order. The N-terminal leucine is usually acetylated in the forms described in catalogues.
Controlled human data is limited, and most published findings come from cell culture or animal work. This makes it difficult to state clinical effects with confidence.
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.