heptapeptide raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
This page was last updated on 2025-08-17 and is reviewed periodically as new material appears.
TB-500 is a catalogue name applied to a synthetic peptide related to thymosin beta-4, an actin-binding protein found in most mammalian cells. Suppliers do not use the label consistently: some describe it as the full 43-residue protein, others as a short fragment from the actin-binding region, and others as a related tetrapeptide. Because the name is commercial rather than chemical, two products sold under it may not contain the same molecule. This naming ambiguity is the first point to check in any description of the material.
The most frequently cited identity is a seven-residue fragment with the sequence LKKTETQ, taken from the actin-binding domain of the parent protein. A separate molecule, N-acetyl-seryl-aspartyl-lysyl-proline, often shortened to Ac-SDKP, derives from the same protein's N-terminal region and appears in overlapping literature. Reported molecular masses therefore differ between sources, and a mass value on its own does not establish which fragment is present. Confirmation requires a defined sequence rather than a single number.
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.
| Property | Value | Notes |
|---|---|---|
| Appearance | White to off-white lyophilized powder | Typical form for short synthetic peptides |
| Solubility class | Freely soluble in water and aqueous buffer | Dissolution aided by gentle mixing, not vigorous shaking |
| Typical storage temperature | −20 °C, desiccated | −80 °C used for long-term holding |
| Common analytical method | Reverse-phase HPLC with UV detection near 214 nm | Identity confirmed separately by mass spectrometry |
| Common synonyms | Thymosin beta-4 fragment; TB4 fragment | Naming varies between suppliers and publications |
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.
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.
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.
Similarly, modifications to the tRNA-linked bases that differ from the host system may reduce the translation of proteins quantitatively and qualitatively. For example, translating a foreign gene in another host system that did not contain the required tRNA resulted in early termination at the codon where the tRNA was missing. Collectively, with heterologous expression, when the host translation systems are different from the native system that the genes are being introduced from, coding errors, frameshifts, or premature or improper sequence termination are frequent. Consequently, this leads to a lower yield of functional proteins or unintended overexpression of the protein. These errors are especially prominent with the significant and unnatural increase in demand for host system biological machinery. Often, this causes the reallocation of cellular resources from normal processes to the production of the heterologous protein. Specifically, this strains tRNA and amino acid supply, quality control systems and secretion systems, as well as NADPH required for anabolic processes. Moreover, unnatural heterologous protein buildup also leads to adverse host effects. Overall the implications are not only evident in low product yields but also host stress responses and decreased host viability. There are many areas of active research addressing these limitations of utilizing heterologous expression, especially in a commercial setting.
=== Elimination === Severe cases require hemodialysis, which is the most rapid method of removing potassium from the body. These are typically used if the underlying cause cannot be corrected swiftly while temporising measures are instituted or there is no response to these measures. Loop diuretics (furosemide, bumetanide, torasemide) and thiazide diuretics (e.g., chlortalidone, hydrochlorothiazide, or chlorothiazide) can increase kidney potassium excretion in people with intact kidney function. Potassium can bind to a number of agents in the gastrointestinal tract. Sodium polystyrene sulfonate (Kayexalate) was approved for this use decades ago, and can be given by mouth or rectally. Sodium polystyrene sulfonate given with sorbitol was uncommonly but convincingly associated with colonic necrosis; this combination is no longer used. Patiromer is taken by mouth and works by binding free potassium ions in the gastrointestinal tract and releasing calcium ions for exchange, thus lowering the amount of potassium available for absorption into the bloodstream and increasing the amount lost via the feces. The net effect is a reduction of potassium levels in the blood serum. Sodium zirconium cyclosilicate is a medication that binds potassium in the gastrointestinal tract in exchange for sodium and hydrogen ions. Onset of effects occurs in one to six hours. It is taken by mouth.
=== Prochirality and three-point attachment === The concept of prochirality is necessary for understanding some aspects of enzyme stereospecificity. Ogston pointed out that when a symmetrical molecule is placed in an asymmetric environment, such as the surface of an enzyme, supposedly identically placed groups become distinguishable. In this way he showed that earlier exclusion of non-chiral citrate as a possible intermediate in the tricarboxylate cycle was mistaken. A coffee mug with one handle is an everyday example of a prochiral object. If it is placed in an achiral corrosive liquid, such as a concentrated acid, then the left and right-hand sides will be corroded equally because there is nothing to distinguish them. However, if the mug is held in a person's right hand it is easy to drink out of the left-hand side but difficult to drink out of the right-hand side. In other words, an achiral environment such as an acid cannot distinguish between the two sides of a prochiral, but a chiral object like a person can. Thus a chiral enzyme such as aconitase can act differently on two apparently equivalent groups on a prochiral molecule, so citrate can be an intermediate in the tricarboxylate cycle.
The overall pulp cavity may become smaller by the addition of secondary or tertiary dentin and cause pulp recession. The lack of sensitivity associated with older teeth is due to receded pulp horns, pulp fibrosis, the addition of dentin, or all these changes. Restorative treatment can be performed without local anaesthesia on older dentitions.
Sources: en.wikipedia.org
lipolysis The metabolic pathway by which triglycerides are broken down via hydrolysis into a glycerol molecule and free fatty acid chains. This primarily takes place in adipocytes to mobilize stored energy when demand is high or supply is low.
=== Spring 1973 strategic situation === In February 1973, as the Khmer Rouge continued to win victories against the Lon Nol regime, American bombing of Cambodia was increased. On 15 March 1973, Nixon had implied during a speech that the United States might go back into Vietnam should the Communists violate the ceasefire, and, as a result, Congress began debating a bill to limit American funding for military operations in Southeast Asia. On 29 March 1973, the withdrawal of the Americans from Vietnam was complete, and on 1 April 1973, the last American POWs were freed. The peace agreement put into effect the "leopard's spot" ceasefire, with the Viet Cong being allowed to rule whatever parts of South Vietnam they held at the time of the ceasefire and all of the North Vietnamese troops in South Vietnam being allowed to stay, putting the Communists in a strong position to eventually take over South Vietnam. Public opinion polls in 1973 showed that 52% of Americans were opposed to military aid to South Vietnam if North Vietnam should violate the Paris peace accords and 71% were against the return of American troops to Vietnam. In April 1973, the CIA estimated the total number of PAVN troops in South Vietnam at 150,000 (about the same as in 1972), whereas Kissinger accused North Vietnam of moving more troops down the Ho Chi Minh Trail. That month, Kissinger met with Tho in Paris to reaffirm their commitment to the Paris peace agreement and to pressure him to stop the Khmer Rouge from overrunning Cambodia.
A low RDW has no clinical significance, but an elevated RDW represents increased variation in red blood cell size, a condition known as anisocytosis. Anisocytosis is common in nutritional anemias such as iron deficiency anemia and anemia due to vitamin B12 or folate deficiency, while people with thalassemia may have a normal RDW. Based on the CBC results, further steps can be taken to investigate anemia, such as a ferritin test to confirm the presence of iron deficiency, or hemoglobin electrophoresis to diagnose a hemoglobinopathy such as thalassemia or sickle cell disease.
Sources: en.wikipedia.org
TB-500 is a trade-style label for a synthetic peptide connected to thymosin beta-4. It is sold mainly through research-chemical channels and is not a single chemically defined product across suppliers.
Not necessarily. Some vendors use the name for the full 43-residue protein, while others apply it to a short actin-binding fragment or to a related tetrapeptide. The sequence should be confirmed from documentation rather than assumed from the label.
No thymosin beta-4 fragment holds marketing approval as a medicine in major jurisdictions. Material offered for sale is typically labelled for laboratory research only.
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.