LC-MS raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
This page was last updated on 2025-11-24 and is reviewed periodically as new material appears.
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.
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.
| 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 |
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.
Published research on the intact protein is substantial, covering actin regulation, cell migration, and wound models. Research using the heptapeptide fragment specifically is far smaller, and much of the circulating material originates in supplier documentation rather than peer-reviewed reports. Where fragment studies do exist, they often employ different sequences, chain lengths, or terminal modifications, which complicates direct comparison across papers. Readers encountering claims about TB-500 should therefore separate evidence about thymosin beta-4 from evidence about the fragment itself.
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.
Reconstitution practices affect downstream measurements. The dry powder is typically dissolved in sterile water or a suitable aqueous buffer, then mixed gently rather than vortexed at high speed. Visible particles or cloudiness suggest incomplete dissolution or contamination and should be investigated. For long-term storage, aliquots should be labeled with concentration, solvent, and date. Open questions include how different buffers alter peptide conformation and whether specific container materials adsorb the peptide. Those variables can change apparent concentration in assays even when the chemical identity is correct.
Lyophilized TB-500 is hygroscopic and should be kept dry before use. The usual storage recommendation for the solid is -20 °C, protected from light and moisture. Once dissolved, the peptide is less stable, and repeated freeze-thaw cycles can promote aggregation or degradation. Laboratories often divide a reconstituted solution into single-use aliquots and store them at -80 °C. Exact stability limits depend on buffer, pH, and concentration, so published data do not define a single universal condition.
=== Television === Link TV, US network The Link (game show), UK, 2014–2015 The Link (TV program), US, 2011 documentary The Link, a TV series by aptn Kids, Canada Link: Eat, Love, Kill, a 2022 South Korean television series
== Further reading == Altschul, SF (1991). "Amino acid substitution matrices from an information theoretic perspective". Journal of Molecular Biology. 219 (3): 555–65. doi:10.1016/0022-2836(91)90193-A. PMC 7130686. PMID 2051488. Dayhoff, M. O.; Schwartz, R. M.; Orcutt, B. C. (1978). "A model of evolutionary change in proteins". Atlas of Protein Sequence and Structure. 5 (3): 345–352. Eddy, SR (2004). "Where did the BLOSUM62 alignment score matrix come from?". Nature Biotechnology. 22 (8): 1035–6. doi:10.1038/nbt0804-1035. PMID 15286655. S2CID 205269887. Henikoff, S; Henikoff, JG (1992). "Amino acid substitution matrices from protein blocks". Proceedings of the National Academy of Sciences of the United States of America. 89 (22): 10915–9. Bibcode:1992PNAS...8910915H. doi:10.1073/pnas.89.22.10915. PMC 50453. PMID 1438297.
Lactation suppression Hyperprolactinemia Adjunctive therapy of prolactin-producing pituitary gland tumors (prolactinomas); Monotherapy of Parkinson's disease in the early phase; Combination therapy, together with levodopa and a decarboxylase inhibitor such as carbidopa, in progressive-phase Parkinson's disease; In some countries also: ablactation and dysfunctions associated with hyperprolactinemia (amenorrhea, oligomenorrhea, anovulation, nonpuerperal mastitis and galactorrhea); Treatment of uterine fibroids. Adjunctive therapy of acromegaly: Cabergoline has low efficacy in suppressing growth hormone levels and is highly efficient in suppressing hyperprolactinemia, which is present in 20–30% of acromegaly cases. Growth hormone and prolactin are similar structurally and have similar effects in many target tissues; therefore, targeting prolactin may help symptoms when growth hormone secretion cannot be sufficiently controlled by other methods. Cabergoline is frequently used as a first-line agent in the management of prolactinomas due to its higher affinity for D2 receptor sites, less severe side effects, and more convenient dosing schedule than the older bromocriptine, though in pregnancy bromocriptine is often still chosen since there is less data on safety in pregnancy for cabergoline.
Naturally occurring silver (47Ag) is composed of the two stable isotopes 107Ag and 109Ag in almost equal proportions, with 107Ag being slightly more abundant (51.839% natural abundance). Notably, silver is the only element with multiple NMR-active isotopes all having spin 1/2. Thus both 107Ag and 109Ag nuclei produce narrow lines in nuclear magnetic resonance spectra. 40 radioisotopes have been characterized with the most stable being 105Ag with a half-life of 41.29 days, 111Ag with a half-life of 7.43 days, and 112Ag with a half-life of 3.13 hours. All of the remaining radioactive isotopes have half-lives that are less than an hour, and the majority of these have half-lives that are less than 3 minutes. This element has numerous meta states, with the most stable being 108mAg (half-life 439 years), 110mAg (half-life 249.86 days) and 106mAg (half-life 8.28 days). Known isotopes of silver range in atomic weight from 92Ag to 132Ag. The primary decay mode before the most abundant stable isotope, 107Ag, is electron capture and the primary mode after is beta decay. The primary decay products before 107Ag are palladium (element 46) isotopes and the primary products after are cadmium (element 48) isotopes. The palladium isotope 107Pd decays by beta emission to 107Ag with a half-life of 6.5 million years. Iron meteorites are the only objects with a high enough palladium/silver ratio to yield measurable variations in 107Ag abundance. Radiogenic 107Ag was first discovered in the Santa Clara meteorite in 1978.
=== Transdermal === There are several methods for transdermal delivery of insulin. Pulsatile insulin uses microjets to pulse insulin into the person, mimicking the physiological secretions of insulin by the pancreas. Jet injection had different insulin delivery peaks and durations as compared to needle injection. Some diabetics may prefer jet injectors to hypodermic injection. Both electricity using iontophoresis and ultrasound have been found to make the skin temporarily porous. The insulin administration aspect remains experimental, but the blood glucose test aspect of "wrist appliances" is commercially available Researchers have produced a watch-like device that tests for blood glucose levels through the skin and administers corrective doses of insulin through pores in the skin. A similar device, but relying on skin-penetrating "microneedles", was in the animal testing stage in 2015. In the last couple of years, the use of chemical enhancers, electrical devices, and microneedle devices has shown tremendous promise for improving the penetration of insulin compared to passive transport via the skin. Transdermal insulin delivery shows a more patient-friendly and minimally invasive approach to daily diabetes care than the conventional hypodermic injection however, additional research is necessary to address issues such as long-term use, delivery efficiency, and reliability, as well as side effects involving inflammation and irritation.
Sources: en.wikipedia.org
=== Hydrogen peroxide formation === Notably, because of its potential in relevant antimicrobial, anti-tumor cell, and/or consumption of amino acids, the interest of researching sv-LAAOs has begun to grow. Many authors have investigated the mechanism of antibacterial action of sv-LAAO. It is well established that sv-LAAO kills and breaks down bacteria by the H2O2 that is produced as a result of the oxidation reaction occurring in the surrounding environment. In one case study, it was reported that the sv-LAAO (isolated from C. durissus cascavella venom) caused the rupture of bacteria membranes while promoting extravasation, or leakage, of plasmatic contents out of the cellular structure. They argued that the amount of hydrogen peroxide generated was sufficient to inhibit bacterial growth, and that the ability of the enzyme to bind to bacterial membranes is not important in its antibacterial activity.
The Communist Chinese captured 39 P-51s from the Nationalists while they were retreating to Taiwan. In August 1949, the People's Liberation Army Air Force formed its first P-51 squadron at Beijing Nanyuan Airport and were tasked of the defending Beijing's airspace from Nationalist Air Force aircraft. On 1 October 1949, when Mao Zedong proclaimed the founding of the People's Republic of China, nine P-51s conducted a fly-past during the military parade in Beijing. By 1950, when Soviet Union began supplying modern military equipment to China, surviving P-51s were relegated to PLAAF's aviation school and 13 P-51s were modified as two-seat trainers. By September 1953, most P-51s were retired from service and only eight P-51s remained in service to teach Ilyushin Il-10 pilots on how to taxi aircraft. Costa Rica The Costa Rican Air Force flew four P-51Ds from 1955 to 1964. Cuba In November 1958, three US-registered civilian P-51D Mustangs were illegally flown separately from Miami to Cuba, on delivery to the rebel forces of the 26th of July Movement, then headed by Fidel Castro during the Cuban Revolution. One of the Mustangs was damaged during delivery and none of them were used operationally. After the success of the revolution in January 1959, with other rebel aircraft plus those of the existing Cuban government forces, they were adopted into the Fuerza Aérea Revolucionaria. Due to increasing US restrictions and lack of spares and maintenance experience, they never achieved operational status.
=== Other uses === Rhodium is used as an alloying agent for hardening and improving the corrosion resistance of platinum and palladium. These alloys are used in furnace windings, bushings for glass fiber production, thermocouple elements, electrodes for aircraft spark plugs, and laboratory crucibles. Other uses include electrical contacts, where it is valued for small electrical resistance, small and stable contact resistance, and great corrosion resistance, and filters and anodes in mammography systems that emit a lower radiation dose than comparable systems using molybdenum. Rhodium plated by either electroplating or evaporation is extremely hard and useful for optical instruments. In automobile manufacturing, rhodium is also used in the construction of headlight reflectors. Rhodium neutron detectors are used in nuclear reactors to measure neutron flux levels—this method requires a digital filter to determine the current neutron flux level, generating three separate signals: immediate, a few seconds delay, and a minute delay, each with its own signal level; all three are combined in the rhodium detector signal. The three Palo Verde nuclear reactors each have 305 rhodium neutron detectors, 61 detectors on each of five vertical levels, providing an accurate 3D "picture" of reactivity and allowing fine tuning to consume the nuclear fuel most economically.
== Contraindications == Ampicillin/sulbactam is contraindicated in individuals who have a history of a penicillin allergy. Symptoms of allergic reactions may range from rash to potentially life-threatening conditions, such as anaphylaxis. Patients who have asthma, eczema, hives, or hay fever are more likely to develop undesirable reactions to any of the penicillins.
==== Viral infection ==== Antiviral treatment is one of the earliest proposed RNAi-based medical applications, and two different types have been developed. The first type is to target viral RNAs. Many studies have shown that targeting viral RNAs can suppress the replication of numerous viruses, including HIV, HPV, hepatitis A, hepatitis B, influenza virus, respiratory syncytial virus (RSV), SARS coronavirus (SARS-CoV), adenovirus and measles virus. The other strategy is to block the initial viral entries by targeting the host cell genes. For example, suppression of chemokine receptors (CXCR4 and CCR5) on host cells can prevent HIV viral entry.
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.
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.