If you have been reading about prohibited list and want a single page that covers the useful parts, this is it: definitions, context, how it is studied, and the questions that come up repeatedly.
Updated 2026-08-01. Numbers and descriptions here follow the published literature rather than marketing material.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Water content | Low in freshly lyophilised material | Rises after repeated opening of the same vial |
| Solution stability | Lower than powder stability | Frozen aliquots are preferred over repeated thawing |
| Purity assessment | Reversed-phase HPLC with UV detection | Peak-area percentage excludes salts and water |
| Salt form | Often the trifluoroacetate salt | Retained from acidic purification gradients |
| Light sensitivity | Not strongly photoreactive | Dark storage still advised for long-term keeping |
Interest in the peptide grew during the 2000s and 2010s, when studies of tendon and ligament injuries in horses reported changes in lesion size after treatment. Those reports circulated widely outside the scientific literature and shaped much of the current online discussion. Subsequent reviews noted inconsistent study design, small groups, and a shortage of independent replication. Popular descriptions often blur the line between the fragment, the complete protein, and unrelated growth factors, which complicates comparisons across sources.
TB-500 is a synthetic peptide whose sequence corresponds to a short fragment near the N-terminus of thymosin beta-4, a small protein present in most mammalian cells. The fragment is commonly cited as containing the actin-binding region of the parent molecule, which is why it appears in laboratory work on cell migration and tissue repair. Suppliers distribute it as a lyophilised powder intended for research use. Its identity is defined by amino acid sequence and by the presence of an acetyl group on the N-terminal residue.
Full-length thymosin beta-4 consists of roughly forty-three amino acids and ranks among the more abundant small proteins in the cytoplasm. The fragment is much shorter, so it cannot reproduce every function attributed to the intact molecule. In cell culture, short actin-binding motifs can interfere with filament dynamics and cell movement, but such observations come from controlled experiments rather than from whole-animal work. Whether a truncated fragment produces the same effects as the parent protein remains an open question.
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.
== Activating reagent == NHS is commonly found in organic chemistry or biochemistry where it is used as an activating reagent for carboxylic acids. Activated acids (carboxylates) can react with amines to form amides for example, whereas a normal carboxylic acid would just form a salt with an amine.
Due to its sedative and tranquilizing properties, it was used to quiet the minds of those with psychosis, help with people who were considered insane, and also to help treat patients with insomnia. However, despite its medicinal values in these cases, it was noted that in cases of psychosis, it could cause anger or depression, and due to the drug's euphoric effects, it could cause depressed patients to become more depressed after the effects wore off because they would get used to being high. The standard medical use of opium persisted well into the 19th century. US president William Henry Harrison was treated with opium in 1841, and in the American Civil War, the Union Army used 175,000 lb (80,000 kg) of opium tincture and powder and about 500,000 opium pills. During this time of popularity, users called opium "God's Own Medicine". One reason for the increase in opiate consumption in the United States during the 19th century was the prescribing and dispensing of legal opiates by physicians and pharmacists to women with "female complaints" (mostly to relieve menstrual pain and hysteria). Because opiates were viewed as more humane than punishment or restraint, they were often used to treat the mentally ill. Between 150,000 and 200,000 opiate addicts lived in the United States in the late 19th century and between two-thirds and three-quarters of these addicts were women. Opium addiction in the later 19th century received a hereditary definition. Dr.
=== Examples === 1 IU of rhEGF is defined as the potency of 0.001 μg of a rhEGF in the "91/530" standard vial. One manufacturer reports that its rhEGF is 1.4 times as potent as the 91/530 standard. 12.5 IU of oxytocin is defined as the potency of 21 μg of pure peptide in the "76/575" standard vial. Before the purification of penicillin was perfected, the amounts were also described in "International Units" (and some non-international arbitrary "units" before them) to account for batch-to-batch variation. See Penicillin § Penicillin units.
Na = nitrogen absorbed in proteins on the test diet Nr = nitrogen incorporated into the body on the test diet However direct measurement of Nr is essentially impossible. It will typically be measured indirectly from nitrogen excretion in urine. Faecal excretion of nitrogen must also be taken into account - this part of the ingested protein is not absorbed by the body and so not included in the calculation of BV. An estimate is used of the amount of the urinary and faecal nitrogen excretion not coming from ingested nitrogen. This may be done by substituting a protein-free diet and observing nitrogen excretion in urine or faeces, but the accuracy of this method of estimation of the amount of nitrogen excretion not coming from ingested nitrogen on a protein-containing diet has been questioned.
Sources: en.wikipedia.org
== Cancer == DPEP1 has been found to be highly expressed in colon tumor cells compared to normal colon cells—one study even found a ≥2 fold over-expression of DPEP1. Increased levels of DPEP1 have also been detected in colorectal cancer patients, suggesting that DPEP1 is a viable marker for disseminated colon tumor cells.
=== Process control === NMR has now entered the arena of real-time process control and process optimization in oil refineries and petrochemical plants. Two different types of NMR analysis are utilized to provide real time analysis of feeds and products in order to control and optimize unit operations. Time-domain NMR (TD-NMR) spectrometers operating at low field (2–20 MHz for 1H) yield free induction decay data that can be used to determine absolute hydrogen content values, rheological information, and component composition. These spectrometers are used in mining, polymer production, cosmetics and food manufacturing as well as coal analysis. High-resolution FT–NMR spectrometers operating in the 60 MHz range with shielded permanent magnet systems yield high-resolution 1H NMR spectra of refinery and petrochemical streams. The variation observed in these spectra with changing physical and chemical properties is modeled using chemometrics to yield predictions on unknown samples. The prediction results are provided to control systems via analogue or digital outputs from the spectrometer.
Steroids are named after the sterol cholesterol which was first described in gall stones from Ancient Greek chole- 'bile' and stereos 'solid'. Gonane, also known as steran or cyclopentanoperhydrophenanthrene, the nucleus of all steroids and sterols, is composed of seventeen carbon atoms in carbon-carbon bonds forming four fused rings in a three-dimensional shape. The three cyclohexane rings (A, B, and C in the first illustration) form the skeleton of a perhydro derivative of phenanthrene. The D ring has a cyclopentane structure. When the two methyl groups and eight carbon side chains (at C-17, as shown for cholesterol) are present, the steroid is said to have a cholestane framework. The two common 5α and 5β stereoisomeric forms of steroids exist because of differences in the side of the largely planar ring system where the hydrogen (H) atom at carbon-5 is attached, which results in a change in steroid A-ring conformation. Isomerisation at the C-21 side chain produces a parallel series of compounds, referred to as isosteroids. Examples of steroid structures are:
TC# 2.A.3 - Amino Acid-Polyamine-Organocation (APC) Superfamily TC# 2.A.18 - Amino Acid/Auxin Permease (AAAP) Family TC# 2.A.23 - Dicarboxylate/Amino Acid:Cation (Na+ or H+) Symporter (DAACS) Family TC# 2.A.26 - Branched Chain Amino Acid:Cation Symporter (LIVCS) Family TC# 2.A.42 - Hydroxy/Aromatic Amino Acid Permease (HAAAP) Family TC# 2.A.78 - Branched Chain Amino Acid Exporter (LIV-E) Family TC# 2.A.95 - 6TMS Neutral Amino Acid Transporter (NAAT) Family TC# 2.A.118 - Basic Amino Acid Antiporter (ArcD) Family TC# 2.A.120 - Putative Amino Acid Permease (PAAP) Family
Metrohm AG is an internationally active producer of precision instruments for chemical analysis, in particular ion analysis, based in Herisau, Switzerland. Metrohm is the leading manufacturer of titration devices and one of the two biggest manufacturers of ion chromatography systems. Besides, the product range includes systems for near-infrared and Raman spectroscopy, electrochemical measurements, and process analytics. These products are used in industries such as pharmaceuticals, food, chemicals, energy, and environmental analysis.
Sources: en.wikipedia.org
Divide it into single-use aliquots and hold them frozen at -20 °C or below, protected from light. Repeated thawing of one container is the main avoidable source of variability.
Mass spectrometry confirms identity, because the measured mass is compared with the value expected from the sequence. Chromatography mainly reports how much of the material elutes as the target peak.
It usually describes the share of the chromatographic peak area recorded at a set wavelength. Salts, residual water, and solvent are excluded from that number, so it is not the same as mass fraction.
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.