Ac-SDKP 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.
Last reviewed on 2026-03-31. 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.
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.
| 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 |
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.
Discussion of TB-500 appears in several distinct literatures that rarely cite one another. Peer-reviewed studies usually describe in vitro assays or small animal experiments and are cautious about extrapolation. Veterinary and sports communities circulate anecdotal reports with limited methodological detail. Commercial listings add a third layer, often using the name interchangeably with thymosin beta-4 even though the two molecules differ in size and sequence. Regulatory status varies by country, and the compound is not a licensed medicine in most jurisdictions, so readers comparing sources should check which molecule and which purity each source actually describes.
TB-500 is a synthetic seven-residue peptide whose sequence, LKKTETQ, matches the N-terminal actin-binding region of thymosin beta-4. It is usually supplied in an N-terminally acetylated form, a modification that blocks the free amino terminus and can influence behavior in solution. In the research literature the same sequence appears under several names, including thymosin beta-4 fragment and shortened thymosin beta-4. Because it is a short peptide rather than the full 43-residue parent protein, its measured properties differ from those reported for thymosin beta-4 as a whole, and the two are not interchangeable in experimental design.
Thymosin beta-4 itself is a small, widely expressed protein that sequesters monomeric actin and participates in cell migration, angiogenesis, and tissue repair. Researchers have examined the shortened fragment as a possible mimic of some of these activities, reasoning that the actin-binding motif lies within the first few residues. Binding to monomeric actin has been observed in cell-free systems. Whether the fragment reproduces the broader effects of the full protein in living tissue remains an open question, and findings from animal models are frequently cited without a clear bridge to human physiology.
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.
One important property of carbon is that it readily forms chains, or networks, that are linked by carbon-carbon (carbon-to-carbon) bonds. The linking process is called polymerization, while the chains, or networks, are called polymers. The source compound is called a monomer. Two main groups of polymers exist: synthetic polymers and biopolymers. Synthetic polymers are artificially manufactured, and are commonly referred to as industrial polymers. Biopolymers occur within a respectfully natural environment, or without human intervention.
== History == In the early 18th century, Jakob Le Mort (1650–1718), a professor of chemistry at Leiden University, prepared an elixir for asthma and called it "paregoric". The word "paregoric" comes from the Greek word "paregoricon" which was originally applied to oratory – to speak, but, more accurately, talk over, soothe, and finally came to have the same meaning as "anodyne". Le Mort's elixir, consisting of "honey, licorice, flowers of Benjamin, and opium, camphor, oil of aniseed, salt of tartar and spirit of wine", appears as "Elixir Asthmaticum" in the London Pharmacopoeia of 1721. Its ingredients were assembled according to the humoral theory of the time. Paregoric was used in various formulations for hundreds of years. Paregoric was a household remedy in the 18th and 19th centuries when it was widely used to control diarrhea in adults and children, as an expectorant and cough medicine, to calm fretful children, and to rub on the gums to counteract the pain from teething. In a memoir of life in Mississippi after the American Civil War, one woman recalled, "I wonder how any of us grew up, the drinking water of the village was so contaminated...All the family was subject to violent attacks of stomach and intestinal trouble. These were called cramp colic, cholera, morbus flux, etc., and no one ever dreamed of connecting them with the drinking supply. My father had a medicine chest filled with paregoric, Jamaica ginger and cholera mixture, which he dispersed freely." A formula for paregoric from Dr. Chase's Recipes (1865):
A House of Lords inquiry finds that former speaker Baroness Frances D'Souza broke rules on "personal honour" by writing to Metropolitan Police Commissioner Sir Mark Rowley on Lords headed notepaper to query multiple breaches of the 20 mph speed limit adding up to £400 in fines. 16 October – Liberal Democrat councillors win six council seats at county and borough level in Surrey following a series of by-elections. 17 October – Rupert Lowe, MP for Great Yarmouth and former Reform UK member, is given a seat on the Public Accounts Committee following support from Conservative MPs. 18 October – Conservative MP George Freeman says he has reported a deepfake video depicting him announcing his defection to Reform UK to the police. 19 October – Reform UK's Linden Kemkaran, the leader of Kent County Council, threatens to expose the "cowards" who leaked a video appearing to show her swearing and telling councillors from her party to "suck it up". V-levels are announced by the Department for Education as a new qualification for 16-year-olds. 20 October – Four Reform UK councillors on Kent County Council – Paul Thomas, Oliver Bradshaw, Bill Barret and Maxine Fothergrill – are suspended from the party following leaked video footage of a heated online meeting. Junior minister Claire Hughes reveals she has been diagnosed with breast cancer, and says she will step back from her role while undergoing treatment. Fiona Goddard and Ellie-Ann Reynolds resign from the grooming gang inquiry panel.
Sources: en.wikipedia.org
Intraocular, into the eye, e.g., some medications for glaucoma or eye neoplasms. Intraosseous infusion (into the bone marrow) is, in effect, an indirect intravenous access because the bone marrow drains directly into the venous system. This route is occasionally used for drugs and fluids in emergency medicine and pediatrics when intravenous access is difficult. Intraperitoneal, (infusion or injection into the peritoneum) e.g. peritoneal dialysis. Intrathecal (into the spinal canal) is most commonly used for spinal anesthesia and chemotherapy. Intrauterine. Intravaginal administration, in the vagina. Intravenous (into a vein), e.g. many drugs, total parenteral nutrition. Intravesical infusion is into the urinary bladder. Intravitreal, through the eye. Subcutaneous (under the skin). This generally takes the form of subcutaneous injection, e.g. with insulin. Skin popping is a slang term that includes subcutaneous injection, and is usually used in association with recreational drugs. In addition to injection, it is also possible to slowly infuse fluids subcutaneously in the form of hypodermoclysis. Transdermal (diffusion through the intact skin for systemic rather than topical distribution), e.g. transdermal patches such as fentanyl in pain therapy, nicotine patches for treatment of addiction and nitroglycerine for treatment of angina pectoris. Perivascular administration (perivascular medical devices and perivascular drug delivery systems are conceived for local application around a blood vessel during open vascular surgery).
== List of people with the surname == Andy Merrifield (born 1960), British Marxist urban theorist Charles T. Merrifield (c. 1924–1957), American uranium miner and murder victim Charles Watkins Merrifield (1827–1884), British mathematician Dave Merrifield (born 1941), Canadian ice hockey player Donald Merrifield (1928–2010), American Jesuit Eric Mowbray Merrifield, South African engineer, inventor of the dolos Flora Merrifield (1859–1943), British suffragist Frankie Merrifield (born 1994), English footballer Frederick Merrifield (1831–1924), English lepidopterist John H. Merrifield (1847–1906), American politician Lane Merrifield, Canadian entrepreneur, co-creator of Club Penguin Leonard Stanford Merrifield (1880–1943), British sculptor Lester Levern Merrifield (1921–2000), American orthodontist Louisa May Merrifield (1906–1953), British poisoner Mary Philadelphia Merrifield (1804–1889), British algologist and writer Michael Merrifield (born 1946/47), American politician Michael Merrifield, English astronomer and professor Ralph Merrifield (1913–1995), English museum curator and archaeologist Renee Merrifield, Canadian politician Rob Merrifield (born 1953), Canadian politician and diplomat Robert Bruce Merrifield (1921–2006), American biochemist, inventor of solid phase peptide synthesis Samuel Merrifield (1904–1982), Australian politician Webster Merrifield (1852–1916), American educator and academic Whit Merrifield (born 1989), American baseball player William Merrifield (1890–1943), Canadian Victoria Cross recipient
Gillnets may be used in fish maw fishing. However, gillnets can have high rates of bycatch. In the Gulf of California, gillnets set by poachers to catch totoaba also inadvertently catch vaquita, a critically endangered porpoise. The population of vaquita dropped 92% from 1997 to 2015, in large part from totoaba poaching. The 2019 documentary Sea of Shadows documented and condemned totoaba poaching and its negative effect on the vaquita population. In the Kikori River Delta of Papua New Guinea, gillnet fishermen trying to target the scaly croaker Nibea squamosa regularly trap elasmobranchs and dolphins as bycatch: targeted fish make up less than a quarter of the total catch.
In anatomy, fibrous joints are joints connected by fibrous tissue, consisting mainly of collagen. These are fixed joints where bones are united by a layer of white fibrous tissue of varying thickness. In the skull, the joints between the bones are called sutures. Such immovable joints are also referred to as synarthroses.
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.
No. Thymosin beta-4 is a 43-residue natural peptide, while TB-500 is a commercial label applied to a short synthetic fragment of it. The two differ in length, sequence coverage and how they are handled in the laboratory.