Everything below concerns actin-binding fragment. We keep the language plain, cite what the science says, and separate well-supported claims from open questions.
Last reviewed on 2026-05-17. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
TB-500 is a shorthand label used in supplier catalogs and online discussion for a short synthetic peptide described as a fragment of thymosin beta-4. Most product listings present it as the N-terminally acetylated heptapeptide Ac-LKKTETQ, a sequence corresponding to the actin-binding region of the parent protein. The name is not a formal chemical designation and does not appear in standard nomenclature systems. Because labeling practices vary between vendors, two products sold under the same name may not contain the same molecule, and the stated sequence should be treated as a claim rather than a fixed definition.
Identity and purity are checked with chromatographic and mass spectrometric methods. Reverse-phase high-performance liquid chromatography separates the peptide from related impurities, while mass spectrometry confirms the expected molecular mass. A certificate of analysis may report a purity percentage, but the laboratory should still verify the material independently. Common quality concerns include truncated sequences, deamidation, oxidation, and residual solvents from synthesis. Because TB-500 is short, some impurities can differ from the target by only a few mass units.
Reconstitution practices affect downstream measurements. The dry powder is typically dissolved in sterile water or a suitable aqueous buffer, then mixed gently rather than vortexed at high speed. Visible particles or cloudiness suggest incomplete dissolution or contamination and should be investigated. For long-term storage, aliquots should be labeled with concentration, solvent, and date. Open questions include how different buffers alter peptide conformation and whether specific container materials adsorb the peptide. Those variables can change apparent concentration in assays even when the chemical identity is correct.
Lyophilized TB-500 is hygroscopic and should be kept dry before use. The usual storage recommendation for the solid is -20 °C, protected from light and moisture. Once dissolved, the peptide is less stable, and repeated freeze-thaw cycles can promote aggregation or degradation. Laboratories often divide a reconstituted solution into single-use aliquots and store them at -80 °C. Exact stability limits depend on buffer, pH, and concentration, so published data do not define a single universal condition.
| Property | Value | Notes |
|---|---|---|
| Reported sequence | Ac-LKKTETQ | Described in most listings as the actin-binding region of thymosin beta-4 |
| Reported molecular weight | Approximately 889 Da | Value shifts with the stated sequence; compare against the certificate of analysis |
| Parent protein length | 43 amino acids | Thymosin beta-4; the fragment covers only a small part of it |
| Common synonyms | TB4 fragment; thymosin beta-4 fragment | Trade-style names rather than formal nomenclature |
| Formal monographs | Not established | Labeling conventions differ by supplier and region |
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.
TB-500 is a synthetic peptide preparation marketed under a name derived from thymosin beta-4, a 43-residue actin-binding protein first isolated from thymus tissue. The full-length protein has a reported molecular mass near 4963 Da, while material sold as TB-500 is often described as a fragment containing the actin-binding motif LKKTETQ. Because suppliers use the name inconsistently, published sources sometimes refer to the same label as a fragment, a synthetic copy, or a related analog. This naming ambiguity complicates direct comparison of reports across studies.
Laboratory work on thymosin beta-4 describes binding to monomeric actin and effects on cell migration, angiogenesis, and inflammatory signaling in cultured cells. Animal models have examined skin, corneal, and cardiac repair after injury, with outcomes reported mainly in preclinical literature. Most of that evidence concerns the parent protein rather than preparations labelled TB-500, so extrapolation from animal findings to a specific commercial product remains uncertain. Whether the two behave identically in living systems has not been established in controlled human studies.
No major regulatory agency has approved TB-500 for therapeutic use, and it holds no pharmacopoeial monograph. The name appears on the World Anti-Doping Agency prohibited list within the class covering peptide hormones, growth factors, and related substances. Detection in doping control relies on mass spectrometric methods applied to urine, often after preparation steps that concentrate the analyte. Discussion of TB-500 therefore clusters in biochemistry, sports medicine, and anti-doping literature rather than in registered clinical trials.
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.
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.
Interest in the compound comes largely from studies of the parent protein, which participates in actin sequestration, cell migration and tissue repair processes. Whether a short fragment reproduces those activities is a separate question that remains open in the published record. Many summaries describe mechanisms by analogy to thymosin beta-4 rather than from direct measurements on the fragment. Claims about activity should be treated as provisional unless a cited study specifies the exact peptide, its purity and the assay used.
== Symbols == A few symbols are in current use in botany. A number of others are obsolete; for example, Linnaeus used planetary symbols ⟨♂⟩ (Mars) for biennial plants, ⟨♃⟩ (Jupiter) for herbaceous perennials and ⟨♄⟩ (Saturn) for woody perennials, based on the planets' orbital periods of 2, 12 and 30 years; and Willd used ⟨♄⟩ (Saturn) for neuter in addition to ⟨☿⟩ (Mercury) for hermaphroditic. The following symbols are still used:
== Medical uses == Cortisone itself is inactive. It must be converted to cortisol by the action of 11β-hydroxysteroid dehydrogenase type 1. This primarily happens in the liver, the main site at which cortisone becomes cortisol after oral or systemic injection, and can thus have a pharmacological effect. After application to the skin or injection into a joint, local cells that express 11β-hydroxysteroid dehydrogenase type 1 instead convert it to active cortisol. A cortisone injection may provide short-term pain relief and may reduce the swelling from inflammation of a joint, tendon, or bursa in, for example, the joints of the knee, elbow and shoulder and into a broken coccyx. Cortisone is used by dermatologists to treat keloids, relieve the symptoms of eczema and atopic dermatitis, and stop the development of sarcoidosis.
Circumcision is one of the oldest surgical procedures in human history, and remains a highly emotional and controversial issue. Many societies hold a wide-ranging perspectives and different cultural, ethical, or social views on circumcision. In some cultures, males are generally required to be circumcised shortly after birth, during childhood or around puberty as part of a rite of passage.
The enzyme converts the trans double bond of a thioester attached to an acyl carrier protein to the corresponding saturated compound using nicotinamide adenine dinucleotide phosphate (NADPH) and a proton as reducing agent. This enzyme belongs to the family of oxidoreductases, to be specific, those acting on the CH-CH group of donor with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is acyl-[acyl-carrier-protein]:NADP+ oxidoreductase (B-specific). Other names in common use include acyl-ACP dehydrogenase, reductase, enoyl-[acyl carrier protein] (reduced nicotinamide, adenine dinucleotide phosphate), NADPH 2-enoyl Co A reductase, enoyl acyl-carrier-protein reductase, enoyl-ACP reductase, and enoyl-[acyl-carrier-protein] reductase (NADPH, B-specific). This enzyme participates in fatty acid biosynthesis.
Sources: en.wikipedia.org
== Integrated Top-Down Proteomics (iTDP) == Further developed, refined, and optimized since the original report of a routine multi-dimensional separation of protein species (most often using isoelectric focusing and then SDS-PAGE), and subsequently coupled with western blotting and MS, this approach was the first to identify the range of protein species/proteoforms in a variety of samples. Currently, the iTDP analytical approach offers the highest proteoform resolution and a routine approach to full proteome analysis (e.g., across the full breadth of species in native proteomes). In the case of 2D-PAGE, spots and/or regions of interest can be excised from the gel, proteolytically digested using well-established methods, and the resulting peptides then assessed using LC/MS/MS to identify canonical amino acid sequences and their inherent PTM (i.e. an 'integration' with BUP). Integration of this sequence information with the isoelectric point (pI) and molecular weight (MW) information from 2DE thus enables definitive identification of proteoforms based on several key defining physico-chemical characteristics. In addition to highly sensitive and quantitative total proteoform detection using fluorescent stains[20]. and notably Coomassie Brilliant Blue as a near-IR dye, gel staining protocols also enable the identification of broad proteoform groups containing the same PTM (e.g. phospho- and glyco-proteoforms). Thus, iTDP utilizes integration of the best available approaches to enable truly comprehensive, deep proteome analyses at the critically necessary level of proteoforms.
UN experts described Trump's actions as constituting an "international crime of aggression", adding that these actions "represent a grave, manifest and deliberate violation of the most fundamental principles of international law, set a dangerous precedent, and risk destabilizing the entire region and the world". The International Commission of Jurists (ICJ) stated that US attacks against Venezuela and the abduction of President Nicolás Maduro violate international law and the UN Charter, and warned against interference in Venezuela's political future.
vary as decreasing monotonic functions of temperature, and the enrichment of multiply D-substituted > multiply 13C-D-substituted > multiply 13C-substituted isotopologues for a same number of substitutions (as shown in this figure).
Sources: en.wikipedia.org
Most listings describe it as a short acetylated peptide with the sequence Ac-LKKTETQ, presented as a region of thymosin beta-4. The label is a trade-style name rather than a standardized chemical name, so the exact content of a given vial depends on the supplier.
No. Thymosin beta-4 is a protein of 43 amino acids, while TB-500 is described as a short fragment of it. The two differ in size, structure, and the range of interactions each can support.
Naming for research peptides is not centrally coordinated, so vendors set their own labels and specifications. Differences in stated sequence, molecular weight, or purity documentation usually trace back to those independent labeling choices.
The dry powder is normally kept at -20 °C, protected from light and moisture. Reconstituted solutions are often divided into aliquots and stored at -80 °C to reduce freeze-thaw damage.