Everything below concerns thymosin beta-4 fragment. We keep the language plain, cite what the science says, and separate well-supported claims from open questions.
Last reviewed on 2025-12-01. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
Identity and purity are assessed with a small set of standard techniques. Reverse-phase high-performance liquid chromatography gives a purity estimate from peak area, usually recorded at 214 or 220 nanometers, where the peptide bond absorbs. Mass spectrometry confirms the expected molecular mass and can reveal truncated or oxidized species. Amino acid analysis or tandem mass spectrometry sequencing can verify the sequence itself. Additional quality attributes include water content, residual trifluoroacetic acid carried over from purification, and endotoxin where the material is intended for biological work.
The compound is most often distributed as a lyophilized powder, appearing white to off-white and forming a loose cake or fluffy solid. It is hygroscopic to some degree, so brief exposure to humid air can add water weight and complicate weighing. The peptide dissolves readily in water and in neutral aqueous buffers, and aqueous solubility is generally described as high, well above the concentrations used in typical assays. Some polar organic solvents are also usable, which matters when a concentrated stock is prepared before dilution into buffer.
| Property | Value | Notes |
|---|---|---|
| Molecular formula | C38H68N10O14 | Acetylated heptapeptide form |
| Monoisotopic mass | 888.5 Da | Average mass about 889 Da |
| Appearance | White to off-white solid | Usually supplied as lyophilised powder |
| Solubility class | Highly water soluble | Also dissolves in aqueous buffers |
| Common synonyms | Tbeta4 fragment, thymosin beta-4 (17-23) | Refer to the same sequence |
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.
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 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.
Biological interest in this peptide centers on its relationship to actin dynamics. Thymosin beta-4 binds monomeric actin through an LKKTET motif, and a short sequence carrying that motif can compete with other actin-binding proteins in cell-free preparations. Investigators propose that such competition shifts the balance between filament assembly and disassembly, which in turn affects how readily a cell extends protrusions and migrates. Most of the supporting observations come from cultured cells and purified protein systems rather than from intact organisms.
Animal work has examined the peptide in models of cardiac injury, skin wounding, and corneal repair, with reported outcomes covering cell migration, inflammatory cell influx, and tissue remodeling. Several of those experiments used the full-length protein or longer fragments instead of the seven-residue sequence, which makes direct comparison between reports difficult. Results are generally described as tissue-dependent, and effect sizes vary considerably across laboratories. Independent replication is uneven, so the overall picture is incomplete rather than settled.
Controlled human trials of the short fragment are scarce. Much of what appears in review articles is extrapolated from animal models or from studies of the parent protein, and literature searches return a larger body of cardiac and ophthalmic work on thymosin beta-4 than on the abbreviated peptide. Regulatory treatment differs by jurisdiction, and in several countries the material is handled as a research chemical rather than an approved therapeutic. Statements about human benefit should be read as provisional.
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.
== Constantly evolving == Since its initial implementation in the early 2000s, the freely available METLIN website has collected comments and suggestions for improvements from users in the biotechnology, pharmaceutical and academic communities ultimately resulting in functionally useful technology for metabolomics as well as hundreds of thousands of other molecular entities. The METLIN interface allows researchers to readily search the database and characterize metabolites and other compounds through features such as accurate mass, single and multiple fragment searching, neutral loss and full spectrum search capabilities. The similarity searching feature introduced in 2008 was designed to expedite the identification process of unknown molecules. Also, METLIN has been used to create a novel multiple reaction monitoring (MRM) library of precursor to fragment ion transitions. The METLIN-MRM transition repository for small-molecule quantitative tandem mass spectrometry was designed to facilitate data sharing across different instruments and laboratories. A new version of generating MRM transitions was introduced in 2026 as uMRM [1], and takes advantage of the original METLIN-MRM concepts. uMRM however is designed to remove isotopes and in-source fragments (ISF) prior to generating MRMs using a spline-fitting method using multiple collision energies. The METLIN database is implemented in the cloud to enable users throughout the world.
In 1957, Polish foreign minister Adam Rapacki proposed the Rapacki Plan for a nuclear free zone in central Europe. Public opinion tended to be favourable in the West, but it was rejected by leaders of West Germany, Britain, France and the United States. They feared it would leave the powerful conventional armies of the Warsaw Pact dominant over the weaker NATO armies. During November 1958, Khrushchev made an unsuccessful attempt to turn all of Berlin into an independent, demilitarized "free city". He gave the United States, Great Britain and France a six-month ultimatum to withdraw their troops from the sectors of West Berlin, or he would transfer control of Western access rights to the East Germans. Khrushchev earlier explained to Mao Zedong that "Berlin is the testicles of the West. Every time I want to make the West scream, I squeeze on Berlin." NATO formally rejected the ultimatum in mid-December and Khrushchev withdrew it in return for a Geneva conference on the German question.
This lowers the temperature of the liquid nitrogen below its boiling point, so that when the specimen is plunged into it, it envelops the specimen closely for a brief period of time and extracts heat from it more efficiently. Even faster cooling can be obtained by plunging specimens into liquid propane or ethane (ethane has been found to be more efficient) cooled very close to their melting points using liquid nitrogen or by slamming the specimen against highly polished liquid nitrogen-cooled metal surfaces made of copper or silver. Secondly, two properties of water itself prevent rapid cryofixation in large specimens. The thermal conductivity of ice is very low compared with that of metals, and water releases of latent heat of fusion as it freezes, defeating rapid cooldown in specimens more than a few micrometres thick.
"Novel Liquid Crystalline Compounds and Polymers,"J.S. Bradshaw, M.L. Lee, K.E. Markides, and B.A. Jones. US Patent Number 4,864,033. Filed: November 27, 1985. Issued: February 1989. "Multi-Element Selective Radio Frequency Plasma Detector for Capillary Gas Chromatography, F. Yang, P. Farnsworth, R. Skelton, K.E. Markides, and M.L. Lee. U.S. Patent Application Serial No. 24,095. Filed: March 12, 1987. Issued: January 25, 1989. "Oligoethylene Oxide Substituted Siloxane Compounds and Polymers," J.S. Bradshaw, M.L. Lee, K.E. Markides, Filed: December, 1987. "Chiral Polysiloxane Compounds and Polymers," J.S. Bradshaw, M.L. Lee, K.E. Markides, Filed: January, 1988. Issued: June 1990. "Chromatographic Arylcarboxamide Polysiloxanes," J.S. Bradshaw, M.L. Lee, K.E. Markides, Filed: June, 1988. Issued: March 1990. "Novel Chiral Copolymers with Oligosiloxane Spacers," J.S. Bradshaw, B.E. Rossiter, B.J. Tarbet, D.F. Johnson, M.L. Lee, K.E. Markides, File No. 9393 CIP. Filed: March 1992. “Encapsulated Nanoparticles for Drug Delivery”, G. Jacobson, R.N. Zare, K.E. Markides, R.R. Shinde and C.H. Contag, File No. 11/748,408, Filed: May 14, 2007.
=== Direct methods === Water content can be directly measured using a drying oven. The oven-dry method requires drying a sample (of soil, wood, etc.) in a special oven or kiln and checking the sample weight at regular time intervals. When the drying process is complete, the sample's weight is compared to its weight before drying, and the difference is used to calculate the sample's original moisture content. Gravimetric water content, u, is calculated via the mass of water
Sources: en.wikipedia.org
=== Regulation === In some jurisdictions, the sale or possession of hypodermic syringes may be controlled or prohibited without a prescription, due to its potential use with illegal intravenous drugs.
These helpers take part in cleaning and fanning eggs and larvae, cleaning the breeding hole and protecting the territory. They have reduced growth rate but gain protection from predators. Brood parasitism also exists among teleosts; minnows may spawn in sunfish nests as well as nests of other minnow species. The cuckoo catfish is known for laying eggs on the substrate as mouthbrooding cichclids collect theirs and the young catfish will eat the cichlid larvae. Filial cannibalism occurs in some teleost families and may have evolved to combat starvation.
Frequent and excessive urination Frequent and excessive thirst Frequent and excessive hunger High blood glucose levels (often over 600 mg/dL or 33 mmol/L) Weakness Fatigue Large amounts of glucose in the urine (glycosuria) Inability to concentrate Electrolyte disturbance Severe ketonuria, and, in DKA, severe ketonemia Low sodium levels
Azoospermia factor (AZF) is one of several proteins or their genes, which are coded from the AZF region on the human male Y chromosome. Deletions in this region are associated with inability to produce sperm. Subregions within the AZF region are AZFa (sometimes AZF1), AZFb and AZFc (together referred to as AZF2). AZF microdeletions are one of the major causes of male infertility for azoospermia (complete absence of sperm in the ejaculate) and severe oligozoospermia (less than 5 million spermatozoa in the ejaculate) males. AZF is the term used by the HUGO Gene Nomenclature Committee. Of the 15% of couples who are affected by infertility, 50% of those cases are due to the male partner. 15-30% of male factor infertility cases can be correlated with genetic abnormalities. One of the most commonly identified genetic abnormalities in male factor infertility are microdeletions on the long arm of the Y chromosome (Yq), specifically at a region known as the azoospermic factor (AZF) region. In certain circumstances, men with AZF mutations can turn to assisted reproductive technologies (ART), such as intracytoplasmic sperm injection (ICSI), to help them overcome their suboptimal sperm quality. However, it may be more important for clinicians to screen for Yq microdeletions, due to a growing body of evidence that AZF microdeletions have the capability to be vertically transmitted to male offspring. Minor et al. demonstrated that an AZFc mutation was vertically transmitted over three generations via fathers receiving reproductive assistance through ICSI.
Sources: en.wikipedia.org
=== Errors in translation === Even though the ribosomes are usually considered accurate and processive machines, the translation process is subject to errors that can lead either to the synthesis of erroneous proteins or to the premature abandonment of translation, either because a TRNA couples to a wrong codon or because a TRNA is coupled to the wrong amino acid. The rate of error in synthesizing proteins has been estimated to be between 1 in 105 and 1 in 103 misincorporated amino acids, depending on the experimental conditions. The rate of premature translation abandonment, instead, has been estimated to be of the order of magnitude of 10−4 events per translated codon.
=== Exposure in pregnancy === Antidepressant exposure (including citalopram) during pregnancy is associated with shorter duration of gestation (by three days), increased risk of preterm delivery (by 55%), lower birth weight (by 75 g), and lower Apgar scores (by <0.4 points). Antidepressant exposure is not associated with an increased risk of spontaneous abortion. It is uncertain whether there is an increased prevalence of septal heart defects among children whose mothers were prescribed an SSRI in early pregnancy.
Peukert argued for an integrated view of Nazi Germany with the social policies to encourage "healthy Aryan" families to have more children, the "social racism" that saw the bodies of "healthy Aryan" women as belonging to the volksgemeinschaft, the effort to sterilize "anti-social families" and the extermination of Jews and Romany as part and parcel of the same project. Likewise, Peukert argued that Nazi Germany was not some freakish "aberration" from the norms of Western civilization, as he noted that the ideas about eugenics and racial superiority that the National Socialists drew upon were widely embraced throughout the Western world. In the same way, Peukert noted in Inside Nazi Germany as part of his argument against the "freakish aberration" view of the Nazi era that homosexual sex had been made illegal in Germany with Paragraph 175 in 1871 and all the Nazis did with the 1935 version of Paragraph 175 was to make it tougher, as the 1935 version of Paragraph 175 made being homosexual in and of itself a criminal offense, whereas the 1871 version of Paragraph 175 had only made homosexual sex a criminal offense. Peukert also noted against the "freakish aberration" view of Nazi Germany that the 1935 version of Paragraph 175 stayed on the statute books in West Germany until 1969 as it was considered to be a "healthy law", leading to German homosexuals who survived the concentration camps continuing to be convicted all through the 1950s and 1960s under exactly the same law that sent them to the concentration camps under the Third Reich.
Sources: en.wikipedia.org
No. TB-500 is a short synthetic peptide matching residues 17 to 23 of thymosin beta-4, while the parent protein contains 43 residues. The fragment lacks the rest of the protein sequence, so the two are related but not identical.
It consists of leucine, lysine, lysine, threonine, glutamic acid, threonine, and glutamine in that order. The N-terminal leucine is usually acetylated in the forms described in catalogues.
Controlled human data is limited, and most published findings come from cell culture or animal work. This makes it difficult to state clinical effects with confidence.
Short transit at ambient temperature is generally tolerated, but long-term storage at room temperature is not recommended. Heat, moisture, and light all accelerate degradation. Cold, dry, dark storage is the conventional choice.