Ac-SDKP comes up often in conversation and rarely with the context attached. Here we lay out the basics in order, then work through the practical considerations.
Updated 2026-07-09. Numbers and descriptions here follow the published literature rather than marketing material.
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.
Literature and online discussion often conflate TB-500 with full-length thymosin beta-4, even though the two differ in size and are not interchangeable in analytical terms. The fragment is produced by solid-phase peptide synthesis, and the product is a defined seven-residue chain rather than a biological extract. Because the term is a trade-style label, two vendors may supply materials of the same nominal sequence but different counter-ion content, purity, or water content. Comparisons across studies are therefore difficult unless the exact sequence and purity are reported.
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.
Material sold under this label typically arrives as a freeze-dried powder in a sealed vial with a certificate of analysis. Such certificates usually report reversed-phase chromatography purity plus a mass confirmation, and stated purities commonly sit between 95 and 99 percent. Counter-ion identity, residual trifluoroacetate, water content, and peptide net weight are separate specifications that a certificate may or may not include. A purity figure alone does not establish sequence identity, so independent mass verification remains the practical check.
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.
| Property | Value | Notes |
|---|---|---|
| Appearance | White to off-white powder | Supplied as a lyophilised cake in sealed vials |
| Solubility class | Freely soluble in water | Polar and charged side chains dominate the sequence |
| Typical storage temperature | -20 °C or below | Dry and dark; a desiccant is often recommended |
| Identity confirmation | Mass spectrometry | Observed mass compared with the theoretical value |
| Common synonyms | Thymosin beta-4 fragment | Also written as T beta 4 fragment 17-23 |
Interest in the fragment grew during the 1990s and 2000s, when it moved from laboratory work into sports and supplement markets. Anti-doping bodies added thymosin beta-4 fragments to prohibited lists, and a small number of adverse analytical findings have been reported in competition testing. Published controlled human trials remain scarce. Most mechanistic evidence comes from cell culture and animal models, and those studies examine endpoints such as cell migration, wound closure and inflammation markers. That evidence supports research interest but does not establish clinical benefit, and broad regenerative claims should be read as unverified.
TB-500 is a short synthetic peptide sold under a trade name rather than a systematic chemical name. Suppliers usually describe it as a fragment of thymosin beta-4 and ship it as a lyophilised powder intended for laboratory use. Because the label is commercial, the exact sequence attributed to it is not fully consistent across catalogues, and some listings present a seven-residue peptide while others describe related fragments of similar length. It is not an approved medicine in any major jurisdiction, and it is handled as a research chemical.
Thymosin beta-4 itself is a natural peptide of 43 residues found in many cell types and body fluids. Its best-characterised function is binding and sequestering actin monomers, which influences cytoskeletal dynamics. The sequence most often associated with TB-500, LKKTETQ, corresponds to part of that actin-binding region. A different fragment, Ac-SDKP, is also derived from the same parent peptide and is studied in its own right, which is one reason discussions of thymosin fragments can become confusing. The two are structurally distinct and are not interchangeable.
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.
Cryoneurolysis, also referred to as cryoanalgesia, is a medical procedure that temporarily blocks nerve conduction along peripheral nerve pathways. The procedure, which inserts a small probe to freeze the target nerve, can facilitate complete regeneration of the structure and function of the affected nerve. Cryoneurolysis has been used to treat a variety of painful conditions.
A similar stele fragment (ES 1027), 57 centimeters high by 42 centimeters wide by 20 deep, depicting Naram-Sin was found a few miles north-east of Diarbekr, at Pir Hüseyin in a well, though this was not its original context. It is said to have been first found in Miyafarkin, a village about 75 kilometers northeast of Diarbekr. Fragments of an alabaster stele representing captives being led by Akkadian soldiers is sometimes attributed to Narim-Sin (or Rimush or Manishtushu) on stylistic grounds. In particular, it is considered as more sophisticated graphically than the steles of Sargon of Akkad or those of Rimush or Manishtushu. Two fragments (IM 55639 and IM 59205) are in the National Museum of Iraq, and one (MFA 66.89) is the Boston Museum. The stele is quite fragmentary, but attempts at reconstitution have been made. Depending on sources, the fragments were excavated in Wasit, al-Hay district, Wasit Governorate, or in Nasiriyah, both locations in Iraq. It is thought that the stele represents the result of the campaigns of Naram-Sin to Cilicia or Anatolia. This is suggested by the characteristics of the booty carried by the soldiers in the stele, especially the metal vessel carried by the main soldier, the design of which is unknown in Mesopotamia, but on the contrary well known in contemporary Anatolia.
Hemoglobin has a quaternary structure characteristic of many multi-subunit globular proteins. Most of the amino acids in hemoglobin form alpha helices, and these helices are connected by short non-helical segments. Hydrogen bonds stabilize the helical sections inside this protein, causing attractions within the molecule, which then causes each polypeptide chain to fold into a specific shape. Hemoglobin's quaternary structure comes from its four subunits in roughly a tetrahedral arrangement. In most vertebrates, the hemoglobin molecule is an assembly of four globular protein subunits. Each subunit is composed of a protein chain tightly associated with a non-protein prosthetic heme group. Each protein chain arranges into a set of alpha-helix structural segments connected together in a globin fold arrangement. Such a name is given because this arrangement is the same folding motif used in other heme/globin proteins such as myoglobin. This folding pattern contains a pocket that strongly binds the heme group. A heme group consists of an iron (Fe) ion held in a heterocyclic ring, known as a porphyrin. This porphyrin ring consists of four pyrrole molecules cyclically linked together (by methine bridges) with the iron ion bound in the center. The iron ion, which is the site of oxygen binding, coordinates with the four nitrogen atoms in the center of the ring, which all lie in one plane. The heme is bound strongly (covalently) to the globular protein via the N atoms of the imidazole ring of F8 histidine residue (also known as the proximal histidine) below the porphyrin ring.
=== Non-pharmacological treatments === A multi-disciplinary care team is often used in the treatment of JIA. One of the ways occupational or physical therapists help young children with JIA is by developing a home therapy program based around play. Exercises are prescribed by both physical therapists and occupational therapists to increase the range a child can move a joint, to strengthen the muscles around a joint, to decrease pain and stiffness and to prevent further limitations in their joint movements. OTs and PTs can provide children with age-appropriate games and activities to allow the children to practice their exercises while playing and socializing with friends. Examples are crafts, swimming, and sports. Surgery is only used to treat the most severe cases of JIA and is now rarely required.
Sources: en.wikipedia.org
=== Age of onset === Feline hypersomatotropism is usually diagnosed in elderly cats. The average age of diagnosis is between 10 and 11 years with a range of 4–17 years. The age range of dogs reported with growth hormone secreting tumours is between 7 and 10 years. The age range of bitches with progestone induced hypersomatotropism is 4–11 years, for bitches with hypersomatotropism resulting from the estrous cycle the age range is between 6 and 13 years.
== Antidepressant research == Two meta-analyses of preliminary clinical trials evaluating the efficacy of St. John's wort for treating mild-to-moderate depression indicated a response similar to selective serotonin reuptake inhibitors and with better tolerance, although the long-term generalization of study results was limited by the short duration (4–12 weeks) of reviewed studies.
== Awards and honors == 1983 - HVA Briscoe Prize 1987 - Du Pont Young Faculty Fellow 1991 - Meldola Medal and Prize by Royal Society of Chemistry 1992 to 1994 - Alcoa Directors Fellowship 1995 - Corday Morgan Medal and Prize 1995 - Fellow, Royal Society of Chemistry 1997 - Hümboldt Senior Scientist Research Award 2002 - Welch Foundation Norman Hackerman Award in Chemical Research 2009 - Prince of Wales Visiting Innovator 2011 - Lifetime Achievement Award in Nanotechnology 2011 - World Technology Award (Materials) 2013 - Applied Inorganic Chemistry Award (Royal Society of Chemistry) 2016 - Erasmus+ Vilnius University 2019 - Star of Asia Award 2020 - Adjunct Professor University of Technology Brunei
Carbon-14 (also called radiocarbon) occurs in trace amounts and has a half-life of 5730 years. The primary source of 14C on Earth is the reaction of 14N with thermal neutrons from cosmic radiation spallation reactions in the upper atmosphere; this mixes throughout the atmosphere, and biological processes such as photosynthesis incorporate the 14C into living organisms. Since organisms stop absorbing 14C upon dying, measurement of the amount of 14C in a sample may be used to estimate its age. This technique, called radiocarbon dating, is one of the principal methods of radiometric dating in archaeology.
1 June – Caltech reports the first successful beaming of solar energy from space down to a receiver on the ground, via the MAPLE instrument on its SSPD-1 spacecraft, launched into orbit in January. 2 June – Physicist Lucas Lombriser proposes a controversial alternative way of interpreting the available scientific data which suggests that the notion of an expanding universe may be more a "mirage" than otherwise. 5 June Scientists report potential evidence that Homo naledi, an extinct species of small-brained archaic human discovered in 2013 in South Africa, and living as long as 500,000 years ago, buried their dead, created art in their caves and used fire. A 'chef' robot developed is trained to watch and learn from cooking videos, and recreate dishes itself. A first global estimate suggests that an equivalent of ~36% of current annual CO2 emissions from fossil fuels is stored by soil mycelium of mycorrhizal fungi yearly. 6 June – A study finds that the first complete disappearance of Arctic sea ice could occur during the 2030s, a decade earlier than previously forecast. 7 June – Scientists report a new mechanism of central nervous system viral diseases including COVID-19 – fusion of brain cells. 8 June US scientists confirm that the next El Niño has begun, likely resulting in higher global temperatures in late 2023 and into 2024. Various statistics show the year is unusual and climate change is already having significant impacts such as an Antarctic sea ice extent anomaly and record-high ocean surface temperatures.
Sources: en.wikipedia.org
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.
It corresponds to the actin-binding region of thymosin beta-4. Commercial synthesis reproduces that seven-residue stretch, usually with an acetyl group on the N-terminus.
It is not authorised as a medicine in the United States or the European Union and is distributed as a research chemical. Labels consequently carry research-use-only statements rather than clinical indications.
Usually not, though usage overlaps. The label most often refers to a short acetylated fragment of the parent protein, while thymosin beta-4 itself is the full 43-residue molecule. Because suppliers vary, a sequence statement is needed to settle the question for any particular lot.