Ac-LKKTETQ 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.
Updated 2025-08-14. Numbers and descriptions here follow the published literature rather than marketing material.
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.
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.
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 |
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.
Detection in biological matrices generally relies on liquid chromatography coupled with tandem mass spectrometry, because the peptide lacks a convenient ultraviolet chromophore beyond the amide backbone. Immunoassays have been described, but antibodies raised against the fragment can cross-react with the full-length protein or with unrelated peptides, so findings usually require confirmation by a second technique. Sample preparation typically involves protein precipitation followed by solid-phase extraction. Reported detection windows depend on dose, route, matrix, and instrument sensitivity.
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.
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.
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.
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.
Hypercalcemia and/or hypercalciuria reflect the known pharmacodynamic actions of parathyroid hormone in the gastrointestinal tract, the kidney and the skeleton, and is therefore an expected undesirable effect. Nausea is another commonly reported adverse reaction to the use of parathyroid hormone.
Devices that integrate multiple laboratory functions on a single chip of only a few square millimeters or centimeters in size and that are capable of handling extremely small fluid volumes down to less than picoliters.
If a Druze individual, whether male or female, marries a non-Druze, they may face ostracism and marginalization from their community. Since a non-Druze partner cannot convert to the Druze faith, the couple cannot have Druze children, as the Druze faith can only be inherited from two Druze parents at birth. Marrying a non-Druze, whether male or female, is viewed as apostasy from the Druze religion. The Druze community holds a negative perception of apostates who marry outside the religion. Consequently, those who leave the Druze religion due to interfaith marriage are forced to leave their village and are exiled to distant, non-Druze areas. This religious and social pressure leads to their isolation and classification as outcasts within their Druze community.
A vault is a large ribonuclear protein particle, a membrane-less organelle, three times the size of a ribosome but with only three proteins in contrast to the near hundred in the ribosome. Most human cells have around 10,000 vaults, and in some types of immune cell there may be up to 100,000. Macrophages have the greatest number of vaults of any human cell. Vaults are largely overlooked because their functions are purely speculative. They may play a role in transport from the nucleus to the cytoplasm, and may serve as scaffolds for signal transduction proteins. They are present in normal tissues, and more so in secretory and excretory epithelial cells.
Sources: en.wikipedia.org
== Structure == SUMO proteins are small; most are around 100 amino acids in length and 12 kDa in mass. The exact length and mass varies between SUMO family members and depends on which organism the protein comes from. Although SUMO has very little sequence identity with ubiquitin (less than 20%) at the amino acid level, it has a nearly identical structural fold. SUMO protein has a unique N-terminal extension of 10-25 amino acids which other ubiquitin-like proteins do not have. This N-terminal is found related to the formation of SUMO chains. The structure of human SUMO1 is depicted on the right. It shows SUMO1 as a globular protein with both ends of the amino acid chain (shown in red and blue) sticking out of the protein's centre. The spherical core consists of an alpha helix and a beta sheet. The diagrams shown are based on an NMR analysis of the protein in solution.
=== brGDGT === The building blocks of brGDGT, specifically the long alkyl groups (iso-diabolic acid), are detected in acidobacteria subdivisions 1, 3, 4, and 6. Small amounts of brGDGT-I was detected in Acidobacteriaceae strain A2-4c by full mass spectrum and tentatively in Acidobacteriaceae strain 307 by single-ion monitoring MS; none has been detected in the 44 other strains tested as of 2018. More complex brGDGTs known from nature have not yet been detected in any cell culture.
== External links == The MEROPS online database for peptidases and their inhibitors: Cysteine Peptidases Archived 2017-04-04 at the Wayback Machine Cysteine+endopeptidases at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
is the observed value. An error of a measurement is an inverse measure of accurate measurement (i.e., smaller the error greater the accuracy of the measurement). Errors can be expressed relatively. Given the relative error (
However, witnesses stated that efforts to organize a proper defense quickly derailed as most officers and soldiers refused to continue resistance or outright fled. There were contradictory orders to soldiers and policemen, with commanders initially ordering them to stay at their positions or to retreat or vice versa. Only Alawite officers reportedly expressed any willingness to defend the capital. Iran began withdrawing its personnel from Syria in the early hours of 6 December 2024, pulling out top commanders of the IRGC's Quds Force and ordering evacuations at the Iranian Embassy in Damascus and at IRGC bases across Syria. Evacuating Iranians headed towards Lebanon and Iraq. China also actively assisted its citizens in leaving the country. On the same day, rebels south of Damascus announced the "Southern Operations Room" (SOR), exploiting the widespread retreat and collapse of loyalist troops in the region. SOR swiftly started to take control of southern towns and rural areas in cooperation with other opposition forces. By the beginning of 7 December 2024, rebels had captured most of Daraa Governorate and Suwayda Governorate and granted safe passage to some pro-government forces towards Damascus. Maher al-Assad, Bashar's brother and head of the 4th Armoured Division, was tasked with defending the capital. Despite the chaos among the Syrian Armed Forces, he actually intended to do so; Maher had reportedly been told that the military's withdrawal from other regions was intended to gather all forces for a last stand at Damascus.
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.