A practical reference on mass confirmation: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
Reviewed 2025-09-19. Anything still debated is marked as such rather than presented as settled.
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.
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.
Identity and purity are usually assessed by reversed-phase high-performance liquid chromatography together with mass spectrometry. The chromatogram provides a purity estimate as a percentage of total peak area, while the mass spectrum confirms that the observed mass matches the expected value. Amino acid analysis or tandem mass spectrometry sequencing can provide additional confirmation. Reported purity figures depend on the column, gradient, and detection wavelength, so values from different laboratories are not directly comparable without method details.
Lyophilised peptide is normally reconstituted with sterile water or a neutral buffer shortly before use. Because repeated freeze-thaw cycles can degrade the material, dividing a reconstituted solution into single-use aliquots is a common practice. Working solutions are usually kept cold and protected from light. The exact shelf life depends on concentration, buffer composition, and handling, so it is often determined empirically rather than assumed.
| Property | Value | Notes |
|---|---|---|
| Molecular mass | ≈889 Da for the 7-residue fragment | Full-length thymosin beta-4 is ≈4.9 kDa; catalogs differ |
| Appearance | White to off-white powder | Hygroscopic; weight shifts with residual moisture |
| Solubility class | Freely soluble in water | Also dissolves in aqueous buffers; poorly soluble in nonpolar solvents |
| Typical storage temperature | −20 °C, desiccated, protected from light | Once rehydrated, short-term holding at 2-8 °C |
| Typical analytical method | Reversed-phase HPLC with mass spectrometry | Purity by UV absorbance; identity by ESI-MS or MALDI-TOF |
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.
The regulatory position is broadly consistent across major jurisdictions: no thymosin beta-4 fragment is an approved medicine, and laboratory material is commonly labelled as not intended for human consumption. Anti-doping rules in sport list thymosin beta-4 and its fragments among prohibited peptide hormones. Because these products travel through research-chemical channels rather than pharmaceutical supply chains, quality varies considerably between vendors. Independent testing of identity, purity and sterility is the only dependable check, and a certificate of analysis describes one batch rather than a supplier's whole catalogue.
Lyophilized peptide powder is normally held desiccated at −20 °C, with −80 °C used for longer storage periods. Allowing a sealed vial to reach room temperature before opening is standard practice, because condensation forming on cold powder introduces moisture. Once dissolved, solutions are typically kept cold and shielded from light. Repeated freeze-thaw cycles are avoided because they encourage aggregation and gradual loss of material. These conventions are general to synthetic peptides rather than unique to any one sequence.
Laboratory work on thymosin beta-4 describes binding to monomeric actin and effects on cell migration, angiogenesis, and inflammatory signaling in cultured cells. Animal models have examined skin, corneal, and cardiac repair after injury, with outcomes reported mainly in preclinical literature. Most of that evidence concerns the parent protein rather than preparations labelled TB-500, so extrapolation from animal findings to a specific commercial product remains uncertain. Whether the two behave identically in living systems has not been established in controlled human studies.
No major regulatory agency has approved TB-500 for therapeutic use, and it holds no pharmacopoeial monograph. The name appears on the World Anti-Doping Agency prohibited list within the class covering peptide hormones, growth factors, and related substances. Detection in doping control relies on mass spectrometric methods applied to urine, often after preparation steps that concentrate the analyte. Discussion of TB-500 therefore clusters in biochemistry, sports medicine, and anti-doping literature rather than in registered clinical trials.
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.
== Relationship to other major ethnic groups in Sri Lanka == A study looking at genetic variation of the FUT2 gene in the Sinhalese and Sri Lankan Tamil population, found similar genetic backgrounds for both ethnic groups, with little genetic flow from other neighbouring Asian population groups. Studies have also found no significant difference with regards to blood group, blood genetic markers (Saha, 1988) and single-nucleotide polymorphism between the Sinhalese and other ethnic groups in Sri Lanka. Another study has also found "no significant genetic variation among the major ethnic groups in Sri Lanka". This is further supported by a study which found very similar frequencies of alleles MTHFR 677T, F2 20210A & F5 1691A in Indian Tamil, Sinhalese, Sri Lankan Tamil, and Sri Lankan Moor populations.
In June 2023, ELEVIDYS (Delandistrogene moxeparvovec) was approved by the FDA for use in 4-5-year-old boys with mutations in the DMD gene. The FDA granted accelerated approval to ELEVIDYS, which requires that the product be further studied to verify its clinical benefit. In June 2024, the U.S. Food and Drug Administration expanded approval of delandistrogene moxeparvovec to include individuals with Duchenne muscular dystrophy with a confirmed mutation in the DMD gene who are at least 4 years of age. The FDA granted traditional approval for ambulatory patients and accelerated approval for non-ambulatory patients.
hypoxanthine (I) A naturally occurring, non-canonical purine nucleobase that is used in some RNA molecules and pairs with standard nucleobases in a phenomenon known as wobble base pairing. Its nucleoside form is known as inosine, which is the reason it is commonly abbreviated with the letter I in sequence reads.
Uptake into the postsynaptic compartment, Re-uptake into the presynaptic compartment, or Uptake into a third, nonneuronal compartment. Postsynaptic neurons remove little glutamate from the synapse. There is active reuptake into presynaptic neurons, but this mechanism appears to be less important than astrocytic transport. Astrocytes could dispose of transported glutamate in two ways. They could export it to blood capillaries, which abut the astrocyte foot processes. However, this strategy would result in a net loss of carbon and nitrogen from the system. An alternate approach would be to convert glutamate into another compound, preferably a non-neuroactive species. The advantage of this approach is that neuronal glutamate could be restored without the risk of trafficking the transmitter through extracellular fluid, where glutamate would cause neuronal depolarization. Astrocytes readily convert glutamate to glutamine via the glutamine synthetase pathway and released into the extracellular space. The glutamine is taken into the presynaptic terminals and metabolized into glutamate by the phosphate-activated glutaminase (a mitochondrial enzyme). The glutamate that is synthesized in the presynaptic terminal is packaged into synaptic vesicles by the glutamate transporter, VGLUT. Once the vesicle is released, glutamate is removed from the synaptic cleft by excitatory amino-acid transporters (EAATs).
Another significant peak is at m/z 257.1536, and corresponds to another fragmentation product with a single ring, and a formula of C17H21O2. Further significant peaks appear at m/z's of 217 and 243, corresponding to formulas of C13H15O2 and C15H19O2, respectively.
Sources: en.wikipedia.org
MR + CO2 → RCO2M where M = Li or MgBr and R = alkyl or aryl. In metal carbon dioxide complexes, CO2 serves as a ligand, which can facilitate the conversion of CO2 to other chemicals. The reduction of CO2 to CO is ordinarily a difficult and slow reaction:
21CFR50.3: Code of Federal Regulations, Title 21--Food and Drugs, Chapter I--Food and Drug Administration, Department of Health and Human Services, Part 50--Protection of Human Subjects, Subpart A--General Provisions, Sec. 50.3 Definitions 21CFR312.3: Code of Federal Regulations, Title 21--Food and Drugs, Chapter I--Food and Drug Administration, Department of Health and Human Services, Part 312--Investigational New Drug Application, Subpart A--General Provisions, Sec. 312.3 Definitions and Interpretations, archived from the original on June 26, 2003 ICH E6: Guidance for Industry - E6 Good Clinical Practice: Consolidated Guidance (PDF), U.S. Department of Health and Human Services, Food and Drug Administration, April 1996, archived from the original (PDF) on July 9, 2009 ICH E9: Guidance for Industry - E9 Statistical Principles for Clinical Trials (PDF), U.S. Department of Health and Human Services, Food and Drug Administration, September 1998, archived from the original (PDF) on July 10, 2009 NCI: Dictionary of Cancer Terms, National Cancer Institute, archived from the original on 2008-10-25, retrieved 2008-10-05 NLM: Glossary of Clinical Trials Terms, U.S. National Library of Medicine, archived from the original on 2011-09-02, retrieved 2008-10-05
==== Breast cancer ==== Although considerable research has examined the potential for soy consumption to lower the risk of breast cancer in women, as of 2016 there is insufficient evidence to reach a conclusion about a relationship between soy consumption and any effects on breast cancer. A 2011 meta-analysis stated: "Our study suggests soy isoflavones intake is associated with a significant reduced risk of breast cancer incidence in Asian populations, but not in Western populations."
chirality A property of asymmetry in which a molecule or ion is distinguishable from its mirror image such that it cannot be superposed upon it by any combination of geometric rotations, translations, or some conformational changes. Such a molecule or ion is said to be chiral, and exists in two forms, known as enantiomers, which are stereoisomers of each other; these forms are distinguished as either "right-handed" or "left-handed" by their absolute configuration or some other criterion. Several different types of asymmetry can give rise to chirality, most commonly when molecules possess stereogenic elements such as one or more stereocenters (central chirality), a stereogenic axis (axial chirality), or a stereogenic plane (planar chirality); additionally, the inherent curvature of a molecule can cause it to possess inherent chirality.
Sources: en.wikipedia.org
Usually not, though usage overlaps. The label most often refers to a short acetylated fragment of the parent protein, while thymosin beta-4 itself is the full 43-residue molecule. Because suppliers vary, a sequence statement is needed to settle the question for any particular lot.
The name is a commercial label rather than a systematic chemical designation, so different vendors and papers attach it to different sequences. Some treat it as a fragment and others as the whole protein. Comparing two reports therefore requires checking what each one actually analyzed.
Typically it reflects the relative area of the main peak in a reversed-phase chromatogram at a given wavelength. It does not confirm the amino acid sequence, the counter-ion, or the amount of peptide by mass. Identity is normally established by a separate mass measurement.
The lyophilised powder is typically held at -20 C or lower in a dry, dark place. Reconstituted solutions are aliquoted and frozen to avoid repeated freeze-thaw cycles.