TB-500 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.
Updated 2026-07-10. Numbers and descriptions here follow the published literature rather than marketing material.
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.
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.
Material is normally supplied as a lyophilised powder in a sealed vial. The powder is hygroscopic, so exposure to humid air leads to water uptake, caking and gradual loss of the fluffy texture that indicates a good freeze-dry. Vials are best kept sealed with desiccant, protected from light and stored cold. Letting a cold vial warm to room temperature before opening reduces condensation on the contents. Purity is normally reported from a chromatographic run, and that figure applies to the batch as tested rather than to the vial after repeated opening.
| Property | Value | Notes |
|---|---|---|
| Appearance | White to off-white powder | Supplied as a lyophilised cake in sealed vials |
| Solubility class | Freely soluble in water | Polar and charged side chains dominate the sequence |
| Typical storage temperature | -20 °C or below | Dry and dark; a desiccant is often recommended |
| Identity confirmation | Mass spectrometry | Observed mass compared with the theoretical value |
| Common synonyms | Thymosin beta-4 fragment | Also written as T beta 4 fragment 17-23 |
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.
Lyophilised peptide powders are hygroscopic, and the fragment absorbs atmospheric moisture when a vial is opened at room temperature. Weighing and aliquoting are normally done quickly in a dry environment, and stock solutions are divided into single-use portions before freezing. Repeated freeze-thaw cycles are avoided because they promote aggregation and can shift the measured content of a vial. These practices are general to synthetic peptides rather than unique to this sequence, but they matter more for short chains kept for long periods.
The seven-residue chain carries several polar and charged side chains, so it dissolves readily in water and in aqueous buffers near neutral pH. No cysteine is present, so disulphide formation is not a concern and reducing agents are unnecessary. Dilute ammonium hydroxide or acetonitrile-water mixtures are sometimes used for stock solutions when initial dissolution is slow. Strongly alkaline conditions and prolonged contact with oxidising agents are avoided because they can modify lysine-containing stretches, and haze in solution usually signals incomplete dissolution or aggregated material.
Identity and purity are checked with reversed-phase high-performance liquid chromatography, which separates the target sequence from truncated or deletion analogues, and with mass spectrometry, which confirms the expected molecular mass. Amino acid analysis and peptide mapping give orthogonal confirmation but are used less often outside specialist laboratories. Counter-ion content varies: material purified on trifluoroacetic acid gradients retains trifluoroacetate, and ion exchange can convert the salt form. Residual water and solvent are measured by Karl Fischer titration or thermogravimetric analysis, and any purity figure should be read together with the method used to obtain it.
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.
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.
In the season fourteen episode "Keep Going", Jimmy confesses to a victim's son that he is now a qualified doctor, having passed his Medical Examiner test (on the third time; he had failed it twice before), but doesn't want the rest of the team to know. However, everyone finds out because he was speaking in front of a mic, and Ducky congratulates him. In season 15, Jimmy takes over as NCIS' Acting Chief Medical Examiner after Ducky takes a sabbatical from NCIS to teach at a New York City medical school, which is extended for Ducky to write a book about his cases and further in season 16 to go on a book tour. In "Bears and Cubs", Ducky announces his official retirement from his full-time NCIS position and permanently promotes Jimmy to Chief Medical Examiner. In season 17, work is starting to consume Jimmy and devour his time. In episode 13, "Sound Off", he is clearly overwhelmed, complaining of only getting 14 minutes of sleep on an autopsy table and in episode 15, "Lonely Hearts", is forced to cancel his plans for Valentine's Day as he has to work overtime to help Gibbs and the team solve a complicated murder case. In episode 19, titled "Blarney", as Jimmy and Kasie eat breakfast together, their morning is interrupted by three armed robbers who decide to hold them hostage after a burglary goes bad. The season 18 episode "The First Day" reveals that Breena died from COVID-19 in December 2020, and that Jimmy was unable to see her before she died because of COVID lockdowns. He was also forced to grieve alone and was unable to give her a real memorial.
The cytoskeleton is found underlying the cell membrane in the cytoplasm and provides a scaffolding for membrane proteins to anchor to, as well as forming organelles that extend from the cell. Indeed, cytoskeletal elements interact extensively and intimately with the cell membrane. Anchoring proteins restricts them to a particular cell surface—for example, the apical surface of epithelial cells that line the vertebrate gut—and limits how far they may diffuse within the bilayer. The cytoskeleton is able to form appendage-like organelles, such as cilia, which are microtubule-based extensions covered by the cell membrane, and filopodia, which are actin-based extensions. These extensions are ensheathed in membrane and project from the surface of the cell in order to sense the external environment and/or make contact with the substrate or other cells. The apical surfaces of epithelial cells are dense with actin-based finger-like projections known as microvilli, which increase cell surface area and thereby increase the absorption rate of nutrients. Localized decoupling of the cytoskeleton and cell membrane results in formation of a bleb.
Because of its central role in controlling eukaryotic gene expression, P-TEFb is subject to stringent regulation at the level of transcription of the genes encoding the subunits, translation of the subunit mRNAs, turnover of the subunits, and also by an unusual mechanism involving the 7SK snRNP. As shown in Figure 3 P-TEFb is held in the 7SK snRNP by the double stranded RNA binding protein HEXIM (HEXIM1 or HEXIM2 in humans). HEXIM bound to 7SK RNA or any double stranded RNA binds to P-TEFb and inhibits the kinase activity. Two other proteins are always found associated with 7SK RNA. The methyl phosphase capping enzyme MEPCE puts a methyl group on the gamma phosphate of the first nucleotide of the 7SK RNA and the La related protein LARP7 binds to the 3' end of 7SK. When P-TEFb is extracted from the 7SK snRNP, 7SK RNA undergoes a conformation change, HEXIM is ejected and hnRNPs take the place of the factors removed. The re-sequestration of P-TEFb requires another rearrangement of the RNA, binding of HEXIM and then P-TEFb. In rapidly growing cells the 7SK snRNP is the predominant form of P-TEFb. For review.
AHCC is widely used in the world and many people use it for general health maintenance and treatment of various diseases. It is often used as a complementary and alternative medicine (CAM) for immune support, as reports in animal and clinical settings have indicated that AHCC is associated with an enhanced response to infection and increased survival. AHCC is in some cases also used by those undergoing conventional cancer therapy (e.g. chemotherapy) for its reported immunomodulatory functions. In Japan, AHCC is the 2nd most popular complementary and alternative medicine used by cancer patients. Agaricus blazei supplements are the most popular, outpacing AHCC use by a factor of 7:1.
Sources: en.wikipedia.org
== Interactions == Substances that act as inhibitors of the CYP3A4 enzyme such as ketoconazole, erythromycin, cimetidine, and furanocoumarin derivatives (found in grapefruit) lead to increased plasma levels of loratadine — that is, more of the drug was present in the bloodstream than typical for a dose. This did not have clinically significant effects in controlled trials of 10 mg loratadine treatment (as opposed to the same studies with Terfenadine (Seldane)). That is, while the drug levels increased, it did not prolong the QTc interval which can lead to the potentially fatal dysrhythmia known as Torsades de Point. Antihistamines should be discontinued 48 hours before skin allergy tests, since these drugs may prevent or diminish otherwise positive reactions to dermal activity indicators.
12 July – NASA releases the first suite of images from the now fully operational James Webb Space Telescope, a day after releasing the Webb's First Deep Field, the image of early universe with the highest resolution. On 14 July, NASA presents images of Jupiter and related areas captured, for the first time, and including infrared views, by the telescope. On 19 July, scientists report what could be the earliest and most distant galaxy ever discovered, GLASS-z12. 13 July The discovery of fast radio burst FRB 20191221A with an unusually long duration of three seconds is reported. A study affirms (see 7 March) that critical slowing down indicators suggest that tropical, arid and temperate forests are substantially losing resilience. On 4 July, Brazil's INPE reports that the country's regions of the Amazon rainforest have been deforested by a record amount in the first half of 2022. A study shows that blood cells' loss of the Y chromosome in a subset of cells, reportedly affecting at least 40% of 70 years-old men to some degree, contributes to fibrosis, heart risks, and mortality in a causal way. Researchers report the development of semitransparent solar cells that are as large as windows, after team members achieved record efficiency with high transparency in 2020. On 4 July, researchers report the fabrication of solar cells with a record average visible transparency of 79%, being nearly invisible.
In normal-phase TLC, the stationary phase is polar. Silica gel is very common in normal-phase TLC. More polar compounds in a sample mixture interact more strongly with the polar stationary phase. As a result, more-polar compounds move less (resulting in smaller RF) while less-polar compounds move higher up the plate (higher RF). A more-polar mobile phase dissolves polar compounds more. As such, all compounds on the TLC plate move higher up the plate in polar solvent mixtures. "Strong" solvents move compounds higher up the plate, whereas "weak" solvents move them less. If the stationary phase is non-polar, like C18-functionalized silica plates, it is called reverse-phase TLC. In this case, non-polar compounds move less and polar compounds move more. The solvent mixture will also be much more polar than in normal-phase TLC.
Sources: en.wikipedia.org
=== Center for Chemical Genomics === A high-throughput screening (HTS) facility is a central component of the Center for Chemical Genomics (CCG). This core facility is designed to assist academic researchers in carrying out high-throughput screens of chemical libraries and to identify new tools for biological research.
== Further reading == David L. Heiserman (1968). Light -Emitting Diodes (PDF). Electronics World. Shuji Nakamura; Gerhard Fasol; Stephen J Pearton (2000). The Blue Laser Diode: The Complete Story. Springer Verlag. ISBN 978-3-540-66505-2.
For services to School Governance and to Children and Young People with Special Educational Needs. Nigel Gavin Begg. Founder, Aspire Technology Solutions. For services to Digital and Technology Industry Growth in North East England. Lynda Janet Suzanne Bennett. For services to Hockey in Wales. Trudy Helen Berlet. Lately Lead Midwife for Bereavement Care, Worcestershire Acute Hospitals NHS Trust. For services to Midwifery. Professor Miriam Bernard. Professor Emerita, Social Gerontology, Keele University. For services to Ageing Research and to Older People. Jane Alison Betsworth. Headteacher, Millfields Community School, London Borough of Hackney. For services to Education. Dr. Sanjay Bhandari. Chair, Kick It Out. For services to Sport. Dr. Manav Bhavsar. Lately Clinical Lead, Critical Care. For services to Healthcare, particularly during Covid-19. Helen Binns. Manager, Families First Team, Leeds City Council. For services to Vulnerable People. Amanda Jayne Bird. Senior Supply Chain Coordinator, Leidos Europe Limited. For services to Defence Logistics. Zachary Birks. Team Leader, Ministry of Defence. For services to Defence. Professor Anthony John Bjourson. Emeritus Professor of Genomics and lately Director, Northern Ireland Centre for Stratified Medicine, Ulster University. For services to Higher Education and to Research. Anthony Grant Bloom. Chairman, Brighton and Hove Albion Football Club. For services to Association Football and to the community in Brighton. Anthony John Bloxham.
Sources: en.wikipedia.org
No. Thymosin beta-4 is a 43-residue protein, while TB-500 matches only residues 17 to 23 of that chain. The two are related but differ in size, and a method that identifies one does not automatically identify the other.
It corresponds to the actin-binding region of thymosin beta-4. Commercial synthesis reproduces that seven-residue stretch, usually with an acetyl group on the N-terminus.
It is not authorised as a medicine in the United States or the European Union and is distributed as a research chemical. Labels consequently carry research-use-only statements rather than clinical indications.
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.