This is a working overview of research chemical, written for readers who want more than a one-paragraph summary but less than a textbook.
This page was last updated on 2025-12-21 and is reviewed periodically as new material appears.
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.
Once dissolved, the peptide is far less stable than the dry powder. Aqueous solutions are subject to hydrolysis, oxidation at susceptible residues and gradual loss of material through adsorption onto glass and plastic surfaces. Terminal glutamine can cyclise under some conditions, producing a related species that complicates purity assessment. Dilute solutions tend to lose a larger fraction of material to surfaces than concentrated ones. Buffers, pH and ionic strength all influence the rate of change, so stability figures are only meaningful when those parameters are stated alongside the storage interval.
Detection in biological samples relies on mass spectrometry, typically liquid chromatography coupled to tandem mass spectrometry after peptide extraction and enrichment. Intact peptides can also be confirmed by high-resolution mass measurement together with fragmentation data. Detection windows in urine are short because the peptide is degraded by proteases and cleared quickly, and concentrations are low. Many jurisdictions treat the compound as a prohibited substance in sport, grouped with peptide hormones and related factors, while it is not an approved therapeutic product. Identity and purity statements therefore rest on certificates of analysis, ideally issued by an independent laboratory.
| Property | Value | Notes |
|---|---|---|
| Common synonyms | Thymosin beta-4 fragment; TB4 fragment | Naming is inconsistent across suppliers and publications |
| Reported sequence | Ac-LKKTETQ | Corresponds to residues 17-23 of the parent protein |
| Frequently cited registry number | 77591-33-4 | Associated with full-length thymosin beta-4 rather than the fragment |
| Common supplied form | Freeze-dried solid | Often presented as an acetate or trifluoroacetate salt |
| Regulatory treatment | Varies by country | Frequently handled as a research chemical; not broadly approved as a therapeutic |
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 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.
Lithium is a teratogen, which can cause birth defects in a small number of newborns. Case reports and several retrospective studies have demonstrated possible increases in the rate of a congenital heart defects (CHDs) including Ebstein's anomaly if taken during the first trimester of pregnancy. The risk is dose-dependent: in the 2017 AMX registry study, the relative risk of "any malformations" is 1.11 in those taking no more than 600 mg of lithium carbonate daily, 1.60 in those taking 601–900 mg daily, and 3.22 in those taking more than 900 mg daily. The first two numbers do not indicate a statistically significant association. In a 2018 meta-analysis, there was a statistically significant 62% increase (95% CI: 12%–133%) in congenital malformations in general, but not for cardiac malformations specifically. Exposure during any part of the pregnancy is associated with a slight but statistically significant increase in the risks of preterm birth and of a larger-than-usual baby at birth. Lithium is effective for preventing relapse during and after pregnancy. As the risks of stopping Lithium can be significant, patients are sometimes recommended to stay on this medicine while pregnant. Careful weighing of the risks and benefits should be made in consultation with a psychiatric physician. The relatively low teratogenic risk of lithium allows such a choice. The decision should be made before the start of pregnancy, as there is no reason for stopping lithium once the pregnancy has started.
HT-2157 (former development code SNAP-37889) is a drug which acts as a selective non-peptide antagonist for the receptor GAL-3, which is usually activated by the neuropeptide galanin. Blocking this receptor with HT-2157 produced increased serotonin release, as well as producing antidepressant and anxiolytic effects in animal studies, and it was also being researched for treatment of cognitive dysfunction. All human clinical trials were terminated due to safety concerns however, and new GAL-3 antagonists are now being sought instead.
=== Muscle Media 2000 ("MM2K") === In 1992, Phillips moved out of his mother's home and changed the publication's format and name to Muscle Media 2000 (usually referred to as "MM2K"). The magazine published frank discussion of the underground aspects of bodybuilding such as the use of and how to smuggle steroids, and columns by writers such as The Steroid Guru Dan Duchaine, Editor-in-Chief TC Luoma, Charles Poliquin, Mike Mooney, Nutritionist Keith Klein CN CCN, and Michael Dullnig M.D. aka "Dr. X." Muscle Media 2000 debuted in March 1992 and featured bodybuilder Lee Labrada on the cover.
While some EU member states have privatised all, and some part, of their telecomms infrastructure, publicly or community-owned internet providers (such as in Denmark or Romania) tend to have the fastest web speeds.
Sources: en.wikipedia.org
=== Aquatic environments === Most PAHs are insoluble in water, which limits their mobility in the environment, although PAHs sorb to fine-grained organic-rich sediments. Aqueous solubility of PAHs decreases approximately logarithmically as molecular mass increases. Two-ringed PAHs, and to a lesser extent three-ringed PAHs, dissolve in water, making them more available for biological uptake and degradation. Further, two- to four-ringed PAHs volatilize sufficiently to appear in the atmosphere predominantly in gaseous form, although the physical state of four-ring PAHs can depend on temperature. In contrast, compounds with five or more rings have low solubility in water and low volatility; they are therefore predominantly in solid state, bound to particulate air pollution, soils, or sediments. In solid state, these compounds are less accessible for biological uptake or degradation, increasing their persistence in the environment.
== Epidemiology == Weissenbacher-Zweymüller syndrome affects males and females in the same numbers. About 30 cases have been reported in medical literature. The disorder can be underdiagnosed causing no true frequency in the population.
He was suspicious of the Soviet Union's motives in supporting African liberation movements, relating that "Russia is as imperialistic as America", although he acknowledged that "in the eyes of the Third World they have a cleaner slate". He also acknowledged that the material assistance provided by the Soviets was "more valuable" to the anti-apartheid cause than the "speeches and wrist-slapping" provided by Western governments. He was cautious of the possibility of a post-apartheid South Africa getting caught up in the imperialist Cold War rivalries of the United States and the Soviet Union.
Sources: en.wikipedia.org
The leading proposal involves sequestration of monomeric actin, which would alter cytoskeletal turnover and cell movement. The actin-binding motif shared with the parent protein is central to that idea. Direct confirmation in whole organisms remains limited.
Very few controlled human studies focus on the seven-residue sequence itself. Most clinical data concern the full-length protein in cardiac or ophthalmic settings. Conclusions drawn for one form should not be assumed to transfer to the other.
Detection normally relies on reversed-phase liquid chromatography paired with mass spectrometry. Chromatographic retention time establishes the expected elution window, and the mass spectrum confirms the molecular ion. Immunoassays exist but can cross-react with related peptides.
Sealed, dry and protected from light at reduced temperature is the usual laboratory convention. Allowing a cold vial to reach room temperature before opening limits condensation. Repeated opening exposes the powder to moisture and should be minimised.