If you have been reading about mass spectrometry 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.
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.
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.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Molecular formula | C38H68N10O14 | Calculated for the acetylated heptapeptide |
| Molecular weight | ~889 Da | Monoisotopic mass approximately 889.0 Da |
| Amino acid sequence | Ac-LKKTETQ | N-terminal acetylated seven-residue peptide |
| Appearance | White to off-white powder | Typically supplied as a lyophilized solid |
| Solubility class | Water-soluble | Peptides of this size generally dissolve in aqueous media |
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.
TB-500 is a laboratory label applied to a short synthetic peptide that is widely described as a fragment of thymosin beta-4, an actin-binding protein present in most mammalian cells. Suppliers and review articles usually present TB-500 as the N-terminal region of that protein, but the exact sequence attached to the name is not consistent across sources. Some product descriptions list a seven-residue chain; others use the label loosely for the parent protein itself. Because of that variation, any technical discussion of TB-500 needs to state which sequence is meant.
Thymosin beta-4 contains 43 amino acids and has a reported molecular mass near 4963 Da. The short fragment most often associated with the TB-500 label, an acetylated chain beginning LKKTETQ, has a reported mass near 889 Da, so the two are easily separated in analytical work. Mass spectrometry and amino acid analysis can confirm which material is present in a given sample. Statements treating TB-500 and thymosin beta-4 as interchangeable are therefore imprecise, even though the two appear together in much of the same literature.
Interest in the compound comes largely from studies of the parent protein, which participates in actin sequestration, cell migration and tissue repair processes. Whether a short fragment reproduces those activities is a separate question that remains open in the published record. Many summaries describe mechanisms by analogy to thymosin beta-4 rather than from direct measurements on the fragment. Claims about activity should be treated as provisional unless a cited study specifies the exact peptide, its purity and the assay used.
Thymosin beta-4 itself is a natural peptide of 43 residues found in many cell types and body fluids. Its best-characterised function is binding and sequestering actin monomers, which influences cytoskeletal dynamics. The sequence most often associated with TB-500, LKKTETQ, corresponds to part of that actin-binding region. A different fragment, Ac-SDKP, is also derived from the same parent peptide and is studied in its own right, which is one reason discussions of thymosin fragments can become confusing. The two are structurally distinct and are not interchangeable.
Interest in the fragment grew during the 1990s and 2000s, when it moved from laboratory work into sports and supplement markets. Anti-doping bodies added thymosin beta-4 fragments to prohibited lists, and a small number of adverse analytical findings have been reported in competition testing. Published controlled human trials remain scarce. Most mechanistic evidence comes from cell culture and animal models, and those studies examine endpoints such as cell migration, wound closure and inflammation markers. That evidence supports research interest but does not establish clinical benefit, and broad regenerative claims should be read as unverified.
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.
Storage recommendations center on keeping the dry powder cold, dry, and dark. A freezer at -20 degrees Celsius or below is conventional, and desiccant is often included to limit moisture uptake. Once dissolved, the peptide is less stable, and solutions are typically kept frozen and thawed only once. Repeated freeze-thaw cycles are a common source of losses because they promote aggregation and adsorption to container surfaces. Working aliquots are therefore prepared in advance, and glass or low-binding plastic is usually preferred over ordinary laboratory plastic.
Glaxo Wellcome had licensed the drug from Sankyo Company of Japan and had sold it in Britain from October 1, 1997. On May 17, 1998, a 55-year-old patient named Audrey LaRue Jones died of acute liver failure after taking troglitazone. Importantly, she had been monitored closely by physicians at the National Institutes of Health (NIH) as a participant in the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) diabetes prevention study. This called into question the efficacy of the monitoring strategy. The NIH responded on June 4 by dropping troglitazone from the study. Dr. David J. Graham, an FDA epidemiologist charged with evaluating the drug, warned on March 26, 1999, of the dangers of using it and concluded that patient monitoring was not effective in protecting against liver failure. He estimated that the drug could be linked to over 430 liver failures and that patients incurred 1,200 times greater risk of liver failure when taking Rezulin. Dr. Janet B. McGill, an endocrinologist who had assisted in the Warner–Lambert's early clinical testing of Rezulin, wrote in a March 1, 2000, letter to Sen. Edward M. Kennedy (D-Mass.): "I believe that the company... deliberately omitted reports of liver toxicity and misrepresented serious adverse events experienced by patients in their clinical studies." On March 21, 2000, the FDA withdrew the drug from the market. Dr. Robert I. Misbin, an FDA medical officer, wrote in a March 3, 2000, letter to Senator John Ashcroft of strong evidence that Rezulin could not be used safely.
The second step in the formation of SCOBY is the introduction of different bacteria into the liquid culture to convert the ethanol product of fermentation into organic acids such as acetic acid, which is a type of ethanol metabolism (lactic acid bacteria may also be added, producing lactic acid from lactic acid fermentation on sugars). A possible byproduct of this reaction is cellulose, which serves as the foundation for the SCOBY biofilm. Like yeasts, the species of bacteria chosen as well as culture conditions directly affect both the characteristics of the liquid kombucha product as well as the composition and morphology of the SCOBY pellicle. While there are many species that have the mechanisms necessary to form cellulose such as Acetobacter and Komagataeibacter, Gluconaceobacter are one of the most populous used, residing in 86–99% of both liquid and biofilm cultures. The necessary culturing conditions of these bacteria are similar to that of yeasts, but require more oxygen due to their aerobic nature in oxidizing ethanol to form organic acids. Once the internal conditions of the co-culture are in place, the symbiotic mixture is left to ferment. Certain studies have claimed optimal fermentation time to be 10 days, but the duration can be modified to change the contents of the yield; greater fermentation times correlate with higher levels of organic acids and other amino acids, which can attribute to the sour undertones of some Kombucha.
== External links == The Miller–Urey experiment website, a simulation of the Miller–Urey Experiment along with a video interview with Stanley Miller] by Scott Ellis from CalSpace (UCSD) Origin-Of-Life Chemistry Revisited: Reanalysis of famous spark-discharge experiments reveals a richer collection of amino acids were formed. Miller–Urey experiment explained Miller experiment with Lego bricks "Stanley Miller's Experiment: Sparking the Building Blocks of Life" on PBS Cairns-Smith, A.G. (1966). "The origin of life and the nature of the primitive gene". Journal of Theoretical Biology. 10 (1): 53–88. Bibcode:1966JThBi..10...53C. doi:10.1016/0022-5193(66)90178-0. PMID 5964688. Details of 2008 re-analysis
Type I present in liver, kidney, thyroid, and (to a lesser extent) pituitary; it accounts for 80% of the deiodination of T4. Type II present in CNS, pituitary, brown adipose tissue, and heart vessel, which is predominantly intracellular. In the pituitary, it mediates negative feedback on thyroid-stimulating hormone. Type III present in placenta, CNS, and hemangioma. This deiodinase converts T4 into reverse T3, which, unlike T3, is inactive. T4 is synthesised in the thyroid follicular cell as follows.
Sources: en.wikipedia.org
Riboswitch sequences (in the mRNA leader transcript) bind molecules such as amino acids, nucleotides, sugars, vitamins, metal ions and other small ligands which cause a conformational change in the mRNA. Most of these attenuators are inhibitory and are employed by genes for biosynthetic enzymes or transporters whose expression is inversely related to the concentration of their corresponding metabolites. Example- Cobalamine biosynthesis, Cyclic AMP-GMP switch, lysin biosynthesis, glycine biosynthesis, fluroide switch etc.
=== Research Award (since 1986) === 2025 Tian (Autumn) Qiu 2024 Elizabeth K. Neumann 2023 Kelly Marie Hines and Stacy Malaker 2022 Gloria Sheynkman 2021 Xin Yan 2019 Eleanor Browne 2014 Kerri A. Pratt 2013 Yu Xia 2012 Ileana M. Cristea and Sharon J. Pitteri 2011 Judit Villen 2010 Sarah Trimpin 2007 Rebecca Jockusch 2006 Heather Desaire 2005 Kristina Hăkansson 2004 Lingjun Li 2003 Andrea Grottoli 2001 Deborah S. Gross 2000 Elaine Marzluff 1998 Mary T. Rodgers 1997 M. Judith Charles 1994 Kimberly A. Prather 1993 Susan Graul 1992 Vicki H. Wysocki 1991 Hilkka I. Kenttämaa 1990 Jennifer Brodbelt 1987 Susan Olesik
==== Section D: Storage and Transport ==== Section D ON Storage and Transport of the IIR is involved in the controlled-temperature logistics and distribution of temperature-sensitive products, from foodstuffs to health products (medicines, vaccines, blood products, organs, etc.), from artwork to chemicals. It addresses all issues of equipment and solutions for a durable cold chain from the production or manufacture to the consumption or use of these products. Section D thus covers the issues of storage, transportation by land, air or water, packaging, distribution and delivery of these products to the consumer, and the traceability of the cold chain. The Section is involved in warehouse and platform equipment, devices for temperature-controlled transport, coolants or cool packs, small coolers and refrigerated containers, chillers, refrigerated furnishings, refrigerated cabinets, climate chambers, refrigerators and freezers, but also in thermometers and temperature recorders. The cold chain involves many temperature ranges, both positive and negative, from -80°C to + 63°C.
Sources: en.wikipedia.org
TB-500 is a synthetic heptapeptide corresponding to a fragment of thymosin beta-4. It is used in laboratory research and is not an approved drug.
No. Thymosin beta-4 is a 43-amino-acid protein, while TB-500 represents only a short N-terminal segment. The two should not be treated as interchangeable in experimental design.
It is often called a thymosin beta-4 fragment, Tβ4 fragment, or Ac-LKKTETQ. The name TB-500 is mainly a commercial or catalog label rather than a formal chemical name.
Sealed, desiccated and protected from light, at -20 °C or lower for long-term storage. Short-term storage at refrigerator temperature is common in working laboratories.