Everything below concerns TB-500. We keep the language plain, cite what the science says, and separate well-supported claims from open questions.
Updated 2025-11-15. Numbers and descriptions here follow the published literature rather than marketing material.
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 shorthand label used in supplier catalogs and online discussion for a short synthetic peptide described as a fragment of thymosin beta-4. Most product listings present it as the N-terminally acetylated heptapeptide Ac-LKKTETQ, a sequence corresponding to the actin-binding region of the parent protein. The name is not a formal chemical designation and does not appear in standard nomenclature systems. Because labeling practices vary between vendors, two products sold under the same name may not contain the same molecule, and the stated sequence should be treated as a claim rather than a fixed definition.
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.
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 |
|---|---|---|
| Reported sequence | Ac-LKKTETQ | Described in most listings as the actin-binding region of thymosin beta-4 |
| Reported molecular weight | Approximately 889 Da | Value shifts with the stated sequence; compare against the certificate of analysis |
| Parent protein length | 43 amino acids | Thymosin beta-4; the fragment covers only a small part of it |
| Common synonyms | TB4 fragment; thymosin beta-4 fragment | Trade-style names rather than formal nomenclature |
| Formal monographs | Not established | Labeling conventions differ by supplier and region |
Dry powder is commonly held at minus twenty degrees Celsius, with some suppliers recommending lower temperatures for long-term archival storage. Once dissolved, solutions are typically kept cold and protected from light, since aqueous peptide solutions can lose integrity through hydrolysis or oxidation over time. Stability data specific to this fragment are limited in the public literature, and much of the guidance comes from general peptide handling practice rather than from controlled degradation studies. Users therefore treat stated shelf lives as approximate rather than fixed.
Identity and purity are normally assessed with reversed-phase high-performance liquid chromatography, paired with mass spectrometry to confirm molecular mass. A certificate of analysis reports a purity percentage, usually derived from chromatographic peak area, but that figure does not by itself prove a correct sequence or the absence of counterions. Independent verification may include amino acid analysis or peptide mapping. Batch-to-batch variation is a documented concern in the research chemical market, and the gap between a quoted purity value and actual peptide content can be substantial when the material is a salt or retains residual water.
Lyophilized peptide arrives as a dry cake that should stay sealed until use. Reconstitution is generally performed with sterile water or a buffered solution, and the resulting liquid should be handled gently to limit mechanical stress. Repeated freeze-thaw cycles are widely described as harmful to short peptides, so dividing a reconstituted batch into single-use portions is a common practice. Laboratories also record the solvent, concentration, and date of preparation on the vial label to keep later measurements traceable.
Purity is normally assessed by reversed-phase HPLC, with the main peak reported as a percentage of total peak area, while identity is confirmed by mass spectrometry. Electrospray and MALDI-TOF instruments are both used, and the observed mass is compared with the value calculated from the stated sequence. Ion-exchange or size-exclusion methods appear where aggregation or charge variants are of interest. Water content, counter-ion content and residual trifluoroacetate from purification are separate variables that can shift the measured mass and should be weighed when reading a certificate of analysis.
Research peptides are typically supplied as a white to off-white lyophilised powder in a sealed vial. The dry solid is more stable than a solution and is normally kept refrigerated or frozen until use. Dissolution is usually done in water, phosphate-buffered saline or a similar aqueous medium, depending on the assay. Because the material is hygroscopic and easily contaminated, opening vials in a low-humidity environment and recording the lot number before use are standard laboratory practices.
Once in solution, short peptides are generally less stable than the dry powder, and repeated freeze-thaw cycles are a common cause of loss. Laboratory guidance usually calls for aliquoting on first dissolution and storing aliquots at -20 °C or below, away from light. Adsorption to plastic and glass surfaces can lower measured concentration, particularly at low concentrations, so container material and buffer choice can affect results. Visible cloudiness, colour change or unexpected precipitate is a signal to re-check the material.
== Further reading == Markwell, John; Brooks, David W. (2002). "Broken Links: The Ephemeral Nature of Educational WWW Hyperlinks". Journal of Science Education and Technology. 11 (2): 105–108. Bibcode:2002JSEdT..11..105M. doi:10.1023/A:1014627511641. Gomes, Daniel; Silva, Mário J. (2006). "Modelling Information Persistence on the Web" (PDF). Proceedings of the 6th International Conference on Web Engineering. ICWE'06. Archived from the original (PDF) on 2011-07-16. Retrieved 14 September 2010. Dellavalle, Robert P.; Hester, Eric J.; Heilig, Lauren F.; Drake, Amanda L.; Kuntzman, Jeff W.; Graber, Marla; Schilling, Lisa M. (31 October 2003). "Going, Going, Gone: Lost Internet References". Science. 302 (5646): 787–788. doi:10.1126/science.1088234. PMID 14593153. Koehler, Wallace (1999). "An Analysis of Web Page and Web Site Constancy and Permanence". Journal of the American Society for Information Science. 50 (2): 162–180. doi:10.1002/(SICI)1097-4571(1999)50:2<162::AID-ASI7>3.0.CO;2-B. Sellitto, Carmine (2005). "The impact of impermanent Web-located citations: A study of 123 scholarly conference publications" (PDF). Journal of the American Society for Information Science and Technology. 56 (7): 695–703. doi:10.1002/asi.20159.
is the consumption rate of A, a reactant. This is equal to the rate expression A is involved in. The rate expression is often related to the fractional conversion both through the consumption of A and through any k changes through temperature changes that are dependent on conversion.
=== Apoptosis === During DNA damage or cellular stress PARPs are activated, leading to an increase in the amount of poly(ADP-ribose) and a decrease in the amount of NAD+. For over a decade it was thought that PARP1 was the only poly(ADP-ribose)polymerase in mammalian cells, therefore this enzyme has been the most studied. Caspases are a family of cysteine proteases that are known to play an essential role in programmed cell death. This protease cleaves PARP-1 into two fragments, leaving it completely inactive, to limit poly(ADP-ribose) production. One of its fragments migrates from the nucleus to the cytoplasm and is thought to become a target of autoimmunity. During caspase-independent apoptosis, also called parthanatos, poly(ADP-ribose) accumulation can occur due to activation of PARPs or inactivation of poly(ADP-ribose)glycohydrolase, an enzyme that hydrolyses poly(ADP-ribose) to produce free ADP-ribose. Studies have shown poly(ADP-ribose) drives the translocation of the apoptosis inducing factor protein to the nucleus where it will mediate DNA fragmentation. It has been suggested that if a failure of caspase activation under stress conditions were to occur, necroptosis would take place. Overactivation of PARPs has led to a necrotic cell death regulated by the tumor necrosis factor protein. Though the mechanism is not yet understood, PARP inhibitors have been shown to affect necroptosis.
Sources: en.wikipedia.org
NIP7: Knockdown reduced mTORC2 activity that is indicated by decreased phosphorylation of mTORC2 substrates. RICTOR: Overexpression leads to metastasis and knockdown inhibits growth factor-induced PKC-phosphorylation. Constitutive deletion of Rictor in mice leads to embryonic lethality, while tissue specific deletion leads to a variety of phenotypes; a common phenotype of Rictor deletion in liver, white adipose tissue, and pancreatic beta cells is systemic glucose intolerance and insulin resistance in one or more tissues. Decreased Rictor expression in mice decreases male, but not female, lifespan. mTOR: Inhibition of mTORC1 and mTORC2 by PP242 [2-(4-Amino-1-isopropyl-1H-pyrazolo[3,4-d]pyrimidin-3-yl)-1H-indol-5-ol] leads to autophagy or apoptosis; inhibition of mTORC2 alone by PP242 prevents phosphorylation of Ser-473 site on AKT and arrests the cells in G1 phase of the cell cycle. Genetic reduction of mTOR expression in mice significantly increases lifespan. PDK1: Knockout is lethal; hypomorphic allele results in smaller organ volume and organism size but normal AKT activation. AKT: Knockout mice experience spontaneous apoptosis (AKT1), severe diabetes (AKT2), small brains (AKT3), and growth deficiency (AKT1/AKT2). Mice heterozygous for AKT1 have increased lifespan. TOR1, the S. cerevisiae orthologue of mTORC1, is a regulator of both carbon and nitrogen metabolism; TOR1 KO strains regulate response to nitrogen as well as carbon availability, indicating that it is a key nutritional transducer in yeast.
== Drugs that bind to prohibitin == Aurilide Fluorizoline Rocaglamide A Prohibitinn in insect Prohibitin (PHB) is a highly conserved eukaryotic protein complex involved in multiple cellular processes. In insects, PHB has been identified as a potential target protein to insecticidal molecules acting as a receptor of PF2 insecticidal lectin in the midgut of Zabrotes subfasciatus larvae (bean pest) and Cry protein of Bacillus thuringiensis in Leptinotarsa decemlineata (Colorado potato beetle).
=== 2000–2011: Established actor and diversification === In 2000, Carrey reteamed with the Farrelly brothers, who had previously directed him in Dumb and Dumber, for the black comedy film Me, Myself & Irene, a film that received mixed reviews but enjoyed box office success. Carrey played the role of state trooper Charlie Baileygates, who has multiple personalities and romances a woman portrayed by Renée Zellweger. That same year, Carrey starred in the second highest-grossing Christmas film of all time, How the Grinch Stole Christmas, playing the title character, for which he received both praise and criticism from critics alongside a Golden Globe nomination. For his next feature film, Carrey starred opposite Jennifer Aniston and Morgan Freeman in Tom Shadyac's international hit comedy Bruce Almighty (2003). Carrey played a television newsman who unexpectedly receives God's omnipotent abilities when the deity decides to take a vacation. The film received mixed reviews upon release but still became a financial success, earning over $484 million worldwide, and going on to become the seventeenth highest-grossing live action comedy of all time. In 2004, Carrey starred in Eternal Sunshine of the Spotless Mind. The film received critical acclaim upon release. Critics highly praised Carrey's portrayal of Joel Barish, in addition to the performance of his co-star Kate Winslet, who was nominated for an Oscar.
==== Effect on bacteria ==== Silver nanoparticles are experimentally shown to inhibit autotrophic nitrifying bacterial growth (86±3%) more than Ag+ ions (42±7%) or AgCl colloids (46±4%). Silver nanoparticle-inhibited heterotrophic growth (55±8%) in Escherichia coli is best observed at lower concentrations, between 1.0 uM and 4.2 uM. This is less than Ag+ ions (~100%), but greater than AgCl colloids (66±6%). The actual cause of these results is undetermined as growth conditions and cell properties differ between nitrifying bacteria and heterotrophic E. coli. Studies conducted in natural lake environments show less response from bacterioplankton than in laboratory environments when exposed to similar concentrations of silver nanoparticles. This may be due to the binding of free Ag+ ions to dissolved organic matter in lake environments, rendering the Ag+ unavailable. Within toothpaste, Ag+ ions have been shown to have a stronger effect on gram-negative bacteria than on gram-positive bacteria. In comparison to other nanoparticles, such as gold, silver tends to have a broader antimicrobial effect, which is another reason why it is incorporated into so many products. Ag+ is less effective on gram-positive bacteria due to the thick layer of peptidoglycan around them that gram-negative species lack. Approximately half of the peptidoglycan wall is composed of teichoic acids linked by phosphodiester bonds, which results in an overall negative charge in the peptidoglycan layer.
Sources: en.wikipedia.org
The engine had a physics system permitting new features, such as monsters hurling corpses at the player or dying characters realistically crumbling into pieces, instead of requiring pre-built animations. Although Troika had ignored first-person engines due to technical limitations, such as a low polygon count and limited texture memory, as the technology improved, it thought it could create a real-time action game without sacrificing the immersion and story of a role-playing game. Describing the choice of developing a game based on the existing White Wolf property over creating their own, Boyarsky said that although an original property lacked the constraints of an existing one, the downside was that it had not been tested and could be rejected by its potential audience; an existing property was proven. Troika tried to stay as close as possible to the White Wolf rules while reducing the number of abilities and disciplines to those relevant to Bloodlines gameplay.
A meta-analysis released subsequently showed that pioglitazone reduced the risk of ischemic cardiac events rather than increased the risk, but increased CHF. A 2020 Cochrane systematic review assessed occurrence of adverse effects with use of pioglitazone, but was not able to reach any conclusions due to insufficient data on included studies.
Lignin is a pervasive natural macromolecule. It comprises about a third of the mass of trees. lignin arises by crosslinking. Related to lignin are polyphenols, which consist of a branched structure of multiple phenolic subunits. They can perform structural roles (e.g. lignin) as well as roles as secondary metabolites involved in signalling, pigmentation and defense.
The Bull's Head Tavern was noted for George Washington's having stopped there for refreshment before riding down to the waterfront to witness the departure of British troops in 1783. Leading to the Post Road, the main route to Boston, the Bowery rivaled Broadway as a thoroughfare; as late as 1869, when it had gained the "reputation of cheap trade, without being disreputable" it was still "the second principal street of the city".
== Spy&Go affinity purification == Mutation of the catalytic glutamic acid residue (E77) in SpyCatcher to alanine stops isopeptide bond formation but does not prevent the initial non-covalent SpyTag/SpyCatcher association. This non-covalent SpyTag/SpyCatcher interaction has been utilized in the affinity purification of SpyTag-fused recombinant proteins. In this purification strategy, termed Spy&Go, resin-immobilized SpyCatcher is used to harvest SpyTag-fused proteins from cell culture supernatants or cell lysates. Non-specifically bound proteins are removed by washing the resin with a neutral buffer and the target protein eluted at neutral pH using high imidazole concentration. The Spy&Go affinity resin is based on SpyCatcher2.1 E77A S49C variant termed SpyDock. SpyDock can be expressed in E. coli as soluble protein, purified using Ni-NTA and anion-exchange resins and immobilized to iodoacetyl-activated agarose through the unpaired cysteine introduced by the S49C substitution. In neutral buffers with physiological salt concentration SpyDock binds to SpyTag- and SpyTag002-fused proteins with affinity in the high nanomolar range (Kd = 750 ± 50 nM for SpyTag, Kd = 73 ± 13 nM for SpyTag002). Affinity to SpyTag003 has not been reported, but requires harsher conditions to ensure full dissociation suggesting it binds tighter. SpyDock-bound proteins are eluted by incubating the resin with 2.5 M imidazole in neutral buffer. The SpyDock resin can be regenerated several times using consecutive washes with 4 M imidazole, 6 M guanidinium hydrochloride and 0.1 M NaOH.
Sources: en.wikipedia.org
Most listings describe it as a short acetylated peptide with the sequence Ac-LKKTETQ, presented as a region of thymosin beta-4. The label is a trade-style name rather than a standardized chemical name, so the exact content of a given vial depends on the supplier.
No. Thymosin beta-4 is a protein of 43 amino acids, while TB-500 is described as a short fragment of it. The two differ in size, structure, and the range of interactions each can support.
Naming for research peptides is not centrally coordinated, so vendors set their own labels and specifications. Differences in stated sequence, molecular weight, or purity documentation usually trace back to those independent labeling choices.
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.