A practical reference on freeze-dried powder: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
This page was last updated on 2026-01-06 and is reviewed periodically as new material appears.
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.
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 synthetic heptapeptide with the sequence Ac-LKKTETQ. It corresponds to a short N-terminal region of thymosin beta-4, a 43-amino-acid protein found in many cell types. The fragment contains an actin-binding motif, which is one reason it appears in laboratory studies of cell migration and cytoskeletal dynamics. TB-500 is not the full-length protein and is produced as a research chemical rather than an approved therapeutic agent. Its molecular weight is approximately 889 Da.
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.
| Property | Value | Notes |
|---|---|---|
| Name type | Commercial trade name | Not a systematic chemical identifier |
| Parent peptide | Thymosin beta-4 | 43-residue natural peptide |
| Common fragment sequence | LKKTETQ | Maps to part of the actin-binding region |
| Molecular size class | Roughly 0.8-1.0 kDa | Depends on exact fragment and terminal modification |
| Regulatory status | Prohibited in sport | Grouped with peptide hormones in many frameworks |
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 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.
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.
Proposed activity centers on actin sequestration and on the movement of cells during repair processes. In cell culture and animal models, the fragment has been associated with migration, tube formation, and tissue remodeling. These observations are frequently described as preliminary, because most published work uses rodent or in vitro systems rather than controlled human trials. Whether the short fragment reproduces the effects of the full protein remains an open question, and the relationship between dose, route, and measured outcome is not well characterized.
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.
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.
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.
== Function == The rectus abdominis is an important postural muscle. It is responsible for flexing the lumbar spine, as when doing a crunch. The rib cage is brought up to where the pelvis is when the pelvis is fixed, or the pelvis can be brought towards the rib cage (posterior pelvic tilt) when the rib cage is fixed, such as in a leg-hip raise. The two can also be brought together simultaneously when neither is fixed in space. The rectus abdominis assists with breathing and plays an important role in respiration when forcefully exhaling, as seen after exercise as well as in conditions where exhalation is difficult such as emphysema. It also helps in keeping the internal organs intact and in creating intra-abdominal pressure, such as when exercising or lifting heavy weights, during forceful defecation or parturition (childbirth).
== Pharmacokinetics == Most of the research on creatine so far has focused on its pharmacological properties. There has been less research into the pharmacokinetics of creatine. Studies have not established pharmacokinetic parameters for clinical usage of creatine such as volume of distribution, clearance, bioavailability, mean residence time, absorption rate, and half life. A clear pharmacokinetic profile would need to be established prior to determine optimal clinical dosing.
== Clinical effects == Kynurenine protects the eye by absorbing UV light, especially in the UVA region (315–400 nm). Kynurenine is present in the lens and retina as one of multiple tryptophan derivatives produced in the eye, including 3-hydroxykynurenine, that together provide UV protection and aid in enhancing visual acuity. The use of kynurenine as a UV filter is consistent with its photostability and low photosensitization, owing to its efficient relaxation from the UV-induced excited state. The concentration of this UV filter decreases with age, and this loss of free kynurenine and the concomitant formation of relatively more photosensitizing kynurenine derivatives and kynurenine-protein conjugates may contribute to the formation of cataracts. Evidence suggests that increased kynurenine production may precipitate depressive symptoms associated with interferon treatment for hepatitis C. Cognitive deficits in schizophrenia are associated with imbalances in the enzymes that break down kynurenine. Blood levels of kynurenine are reduced in people with bipolar disorder. Kynurenine production is increased in Alzheimer's disease and cardiovascular disease where its metabolites are associated with cognitive deficits and depressive symptoms. Kynurenine is also associated with tics. Myokines regulate its metabolism. Kynurenine has also been identified as one of two compounds that makes up the pigment that gives the goldenrod crab spider its yellow color.
Sources: en.wikipedia.org
=== Michael McDonald years === Under contract to release another album in 1976, the Doobies were at a crossroads. Their primary songwriter and singer remained unavailable, so they turned to McDonald and Porter for material to supplement that of Simmons. The resulting LP, Takin' It to the Streets, debuted a radical change in their sound. Their electric guitar-based rock and roll gave way to a more soft rock and blue-eyed soul sound, emphasizing keyboards and horns and subtler, more syncopated rhythms. Baxter contributed jazz-inflected guitar stylings reminiscent of Steely Dan, along with unusual, complex harmony and longer, more developed melody. Above all, McDonald's voice became the band's new signature sound. Takin' It to the Streets featured McDonald's title track and "It Keeps You Runnin'", both hits. (A second version of "It Keeps You Runnin'", performed by Carly Simon, appeared on her album Another Passenger, with the Doobies backing her.) Bassist Porter wrote and sang "For Someone Special" as a tribute to the absent Johnston. A greatest hits compilation, Best of the Doobies, followed before year's end. (In 1996, the Recording Industry Association of America certified Best of the Doobies "Diamond" for sales in excess of 10 million units.) Their new sound was further refined, and McDonald's dominant role cemented with 1977's Livin' on the Fault Line. It featured a recording of the Motown classic "Little Darling (I Need You)" and "Echoes of Love", which had been written by Willie Mitchell for, but not recorded by, Al Green.
=== Metalloproteins and inorganic cofactors === Metalloproteins—in which the active site is a transition metal ion (or metal-sulfide cluster) often coordinated by sulfur atoms of cysteine residues—are essential components of enzymes involved in electron transfer processes. Examples include plastocyanin (Cu2+) and nitrous oxide reductase (Cu–S). The function of these enzymes is dependent on the fact that the transition metal ion can undergo redox reactions. Other examples include many zinc proteins, as well as iron–sulfur clusters. Most pervasive are the ferrodoxins, which serve as electron shuttles in cells. In bacteria, the important nitrogenase enzymes contain an Fe–Mo–S cluster and is a catalyst that performs the important function of nitrogen fixation, converting atmospheric nitrogen to ammonia that can be used by microorganisms and plants to make proteins, DNA, RNA, alkaloids, and the other organic nitrogen compounds necessary for life. Sulfur is also present in molybdenum cofactor.
A β-helix is formed from repeating structural units consisting of two or three short β-strands linked by short loops. These units "stack" atop one another in a helical fashion so that successive repetitions of the same strand hydrogen-bond with each other in a parallel orientation. See the β-helix article for further information. In lefthanded β-helices, the strands themselves are quite straight and untwisted; the resulting helical surfaces are nearly flat, forming a regular triangular prism shape, as shown for the 1QRE archaeal carbonic anhydrase at right. Other examples are the lipid A synthesis enzyme LpxA and insect antifreeze proteins with a regular array of Thr sidechains on one face that mimic the structure of ice.
Antithrombin is a serpin (serine protease inhibitor) and is thus similar in structure to most other plasma protease inhibitors, such as alpha 1-antichymotrypsin, alpha 2-antiplasmin and Heparin cofactor II. The physiological target proteases of antithrombin are those of the contact activation pathway (formerly known as the intrinsic pathway), namely the activated forms of Factor X (Xa), Factor IX (IXa), Factor XI (XIa), Factor XII (XIIa) and, to a greater extent, Factor II (thrombin) (IIa), and also the activated form of Factor VII (VIIa) from the tissue factor pathway (formerly known as the extrinsic pathway). The inhibitor also inactivates kallikrein and plasmin , also involved in blood coagulation. However it inactivates certain other serine proteases that are not involved in coagulation such as trypsin and the C1s subunit of the enzyme C1 involved in the classical complement pathway. Protease inactivation results as a consequence of trapping the protease in an equimolar complex with antithrombin in which the active site of the protease enzyme is inaccessible to its usual substrate. The formation of an antithrombin-protease complex involves an interaction between the protease and a specific reactive peptide bond within antithrombin. In human antithrombin this bond is between arginine (arg) 393 and serine (ser) 394 (see Figure 2 and Figure 3). It is thought that protease enzymes become trapped in inactive antithrombin-protease complexes as a consequence of their attack on the reactive bond.
Sources: en.wikipedia.org
In 1992, Hooters sponsored NASCAR driver Alan Kulwicki as he won the Winston Cup Championship, beating Bill Elliott by ten points, the closest margin in NASCAR prior to The Chase era. On April 1, 1993, Kulwicki, along with several others including Hooters Chairman Bob Brooks's son Mark, were killed in a plane crash near Bristol, Tennessee. They were flying back to the track for Sunday's race after making a sponsor appearance at a Hooters in Knoxville, Tennessee. Hooters remained in the sport, sponsoring drivers like Loy Allen Jr., Rick Mast and Brett Bodine before ending their involvement in 2003. The restaurant returned to NASCAR in 2007 to sponsor a Craftsman Truck Series team led by Jason White, Derrike Cope and Brad Keselowski. Six years later, Hooters sponsored Nationwide Series driver Nelson Piquet Jr.'s car. For the 2016 Bojangles' Southern 500 at Darlington Raceway, Hooters made a comeback in the Cup Series with a one-off paint scheme for Greg Biffle. Hooters most recently sponsored the No. 9 of Chase Elliott from 2017 to 2024. Hooters has sponsored the Major League Eating-sanctioned "Hooters Worldwide Wing Eating Championship" since 2012. Hooters has also licensed its name for the Hooters Road Trip PlayStation racing game. Furthermore, Hooters licensed the Hooters Calendar for Hooters Calendar Girl, a mobile wallpaper application, and Hooters Calendar Girl Tubin', a mobile game, both by Oasys Mobile. It was also one of several real world brands that appeared in the 2011 video game Homefront.
=== Available forms === Mephedrone can come in capsules, tablets, or white powder, which users may swallow, insufflate, inject, smoke, or use rectally. When taken orally, users reported they could feel the effects within 15–45 minutes; when snorted, the effects were felt within minutes and peaked within half an hour. The effects last for between two and three hours when taken orally or nasally, but only half an hour if taken intravenously. It is sometimes sold mixed with methylone in a product called bubbles in the UK and also mixed with other cathinones, including ethcathinone, butylone, fluoromethcathinone and methedrone.
Two more atoms followed on November 12 and 17. (Yet another was originally reported to have been found on November 11, but it turned out to be based on data fabricated by Victor Ninov, and was later retracted.) In the same series of experiments, the same team also carried out the reaction using heavier nickel-64 ions. During two runs, 9 atoms of 271Ds were convincingly detected by correlation with known daughter decay properties:
Sources: en.wikipedia.org
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.
Published work usually examines actin binding, cell migration and tissue repair endpoints in cell and animal models. Findings are generally described as preliminary, and controlled human data remain limited.
Because TB-500 is a trade name rather than a chemical identifier, different vendors and papers may attach it to different fragment lengths. Checking the stated sequence is the practical way to resolve the ambiguity.
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.