If you have been reading about counter-ion 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 2025-12-11. 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.
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.
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.
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.
| 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 |
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.
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.
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.
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.
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.
Purity and identity are separate measurements and are often confused. Reverse-phase high-performance liquid chromatography, usually with ultraviolet detection near 214 nanometres, reports the share of total peak area belonging to the target compound. Mass spectrometry by electrospray or matrix-assisted laser desorption then checks whether the observed mass matches the expected sequence. Neither measurement alone shows that a vial holds the intended peptide. Peptide content, meaning the fraction of vial mass that is genuine peptide rather than counter-ion, water or residual acid, is reported separately and is frequently lower than the stated purity figure.
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.
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.
==== MeSH D12.125.072 – amino acids, cyclic ==== MeSH D12.125.072.050 – amino acids, aromatic MeSH D12.125.072.050.342 – dextrothyroxine MeSH D12.125.072.050.685 – phenylalanine MeSH D12.125.072.050.685.400 – dihydroxyphenylalanine MeSH D12.125.072.050.685.400.180 – cysteinyldopa MeSH D12.125.072.050.685.400.500 – levodopa MeSH D12.125.072.050.685.400.600 – methyldopa MeSH D12.125.072.050.685.440 – fenclonine MeSH D12.125.072.050.685.450 – p-fluorophenylalanine MeSH D12.125.072.050.685.500 – melphalan MeSH D12.125.072.050.767 – thyroxine MeSH D12.125.072.050.767.741 – thyronines MeSH D12.125.072.050.767.741.180 – diiodothyronines MeSH D12.125.072.050.767.741.894 – triiodothyronine MeSH D12.125.072.050.767.741.947 – triiodothyronine, reverse MeSH D12.125.072.050.850 – tryptophan MeSH D12.125.072.050.850.479 – 5-hydroxytryptophan MeSH D12.125.072.050.875 – tyrosine MeSH D12.125.072.050.875.064 – betalains MeSH D12.125.072.050.875.064.500 – betacyanins MeSH D12.125.072.050.875.130 – dihydroxyphenylalanine MeSH D12.125.072.050.875.130.180 – cysteinyldopa MeSH D12.125.072.050.875.130.500 – levodopa MeSH D12.125.072.050.875.130.600 – methyldopa MeSH D12.125.072.050.875.262 – diiodotyrosine MeSH D12.125.072.050.875.379 – melanins MeSH D12.125.072.050.875.496 – monoiodotyrosine MeSH D12.125.072.050.875.664 – methyltyrosines MeSH D12.125.072.050.875.664.050 – alpha-methyltyrosine MeSH D12.125.072.050.875.750 – phosphotyrosine MeSH D12.125.072.170 – cycloleucine MeSH D12.125.072.200 – desmosine MeSH D12.125.072.329 – histidine MeSH D12.125.072.329.269 – ergothioneine MeSH D12.125.072.329.539 – methylhistidines MeSH D12.125.072.401 – imino acids MeSH D12.125.072.401.200 – azetidinecarboxylic acid MeSH D12.125.072.401.623 – proline MeSH D12.125.072.401.623.270 – captopril MeSH D12.125.072.401.623.374 – fosinopril MeSH D12.125.072.401.623.478 – hydroxyproline MeSH D12.125.072.401.761 – pyrrolidonecarboxylic acid MeSH D12.125.072.401.830 – technetium tc 99m diethyl-iminodiacetic acid MeSH D12.125.072.401.840 – technetium tc 99m disofenin MeSH D12.125.072.401.900 – technetium tc 99m lidofenin MeSH D12.125.072.415 – isodesmosine
==== Scales ==== The Schmidt sting pain index and Starr sting pain index are pain scales rating the relative pain caused by different hymenoptera stings. Schmidt has refined his pain index (with a 1–4 scale) with extensive anecdotal experience, culminating in a paper published in 1990 which classifies the stings of 78 species and 41 genera of Hymenoptera. The Starr sting pain scale uses the same 1–4 scale.
Creatine kinase (CK) test: measures the circulating blood levels of creatine kinase an enzyme found in the heart (CK-MB), brain (CK-BB) and skeletal muscle (CK-MM). Blood urea nitrogen (BUN) test: urea nitrogen is the byproduct of protein metabolism first formed in the liver then removed from the body by the kidneys. The BUN test is primarily used to test kidney function. A low BUN level may indicate the effects of malnutrition. BUN-to-creatinine ratio: A BUN to creatinine ratio is used to predict various conditions. A high BUN/creatinine ratio can occur in severe hydration, acute kidney failure, congestive heart failure, and intestinal bleeding. A low BUN/creatinine ratio can indicate a low protein diet, celiac disease, rhabdomyolysis, or cirrhosis of the liver. Thyroid function tests: tests used to assess thyroid functioning by checking levels of thyroid-stimulating hormone (TSH), thyroxine (T4), and triiodothyronine (T3).
The Double-A classification usually hosts developing players that have been part of professional baseball for only a couple of years. These players can get to the Double-A level by earning a promotion from any of the lower-level leagues, with High-A being immediately below Double-A in the minor league hierarchy. The step up to the Double-A level can be one of the hardest promotions for such players because it is the level at which pitchers need to have a good off-speed pitch in their repertoires. In addition, it is the level where fastball-only hitters need to learn how to hit off-speed pitches, or their hopes of advancing to the majors will diminish. Some players may be placed in Double-A to begin their minor league careers, usually veterans from foreign leagues or top prospects out of college. Additionally, major league clubs sometimes send players to their Double-A team to rehabilitate from injuries. While Triple-A is the highest level in the minor leagues, players may also advance to the major leagues directly from Double-A. For example, within the Toronto Blue Jays organization, 17 position players were promoted from Double-A directly to MLB during 1978–2018; approximately one player every two seasons. As players at the Double-A level are, generally, still improving their skills, it could be argued that the pure talent level is higher in Double-A than Triple-A, where there may be some stagnation of talent.
== Residual topology == Residual topology is a descriptive stereochemical term to classify a number of intertwined and interlocked molecules, which cannot be disentangled in an experiment without breaking of covalent bonds, while the strict rules of mathematical topology allow such a disentanglement. Examples of such molecules are rotaxanes, catenanes with covalently linked rings (so-called pretzelanes), and open knots (pseudoknots) which are abundant in proteins. The term "residual topology" was suggested on account of a striking similarity of these compounds to the well-established topologically nontrivial species, such as catenanes and knotanes (molecular knots). The idea of residual topological isomerism introduces a handy scheme of modifying the molecular graphs and generalizes former efforts of systemization of mechanically bound and bridged molecules.
Sources: en.wikipedia.org
In 1867, the Austro-Hungarian compromise and the introduction of the dual monarchy left the Czechs and their aristocracy without the recognition of separate Bohemian state rights for which they had hoped. Bohemia remained part of the Austrian Crown Lands. In Bohemia, opposition to dualism took the form of isolated street demonstrations, resolutions from district representations, and even open air mass protest meetings, confined to the biggest cities, such as Prague. The Czech newspaper Národní listy complained that the Czechs had not yet been compensated for their wartime losses and sufferings during the Austro-Prussian War, and had just seen their historic state rights tossed aside and their land subsumed into the "other" half of the Austro-Hungarian Monarchy, commonly called "Cisleithania". The Czech hopes were revived again in 1870–1871. In an Imperial Rescript of 26 September 1870, Franz Joseph referred again to the prestige and glory of the Bohemian Crown and to his intention to hold a coronation. Under Minister-President Karl Hohenwart in 1871, the government of Cisleithania negotiated a series of fundamental articles spelling out the relationship of the Bohemian Crown to the rest of the Habsburg Monarchy. On 12 September 1871, Franz Joseph announced:
Medieval blast furnaces were about 10 feet (3.0 m) tall and made of fireproof brick; forced air was usually provided by hand-operated bellows. Modern blast furnaces have grown much bigger, with hearths fourteen meters in diameter that allow them to produce thousands of tons of iron each day, but essentially operate in much the same way as they did during medieval times. In 1709, Abraham Darby I established a coke-fired blast furnace to produce cast iron, replacing charcoal, although continuing to use blast furnaces. The ensuing availability of inexpensive iron was one of the factors leading to the Industrial Revolution. Toward the end of the 18th century, cast iron began to replace wrought iron for certain purposes, because it was cheaper. Carbon content in iron was not implicated as the reason for the differences in properties of wrought iron, cast iron, and steel until the 18th century. Since iron was becoming cheaper and more plentiful, it also became a major structural material following the building of the innovative first iron bridge in 1778. This bridge still stands today as a monument to the role iron played in the Industrial Revolution. Following this, iron was used in rails, boats, ships, aqueducts, and buildings, as well as in iron cylinders in steam engines. Railways have been central to the formation of modernity and ideas of progress and various languages refer to railways as iron road (e.g. French chemin de fer, German Eisenbahn, Turkish demiryolu, Russian железная дорога, Chinese, Japanese, and Korean 鐵道, Vietnamese đường sắt).
=== Overall survival === Overall survival is based on death from any cause, not just the condition being treated, thus it picks up death from side effects of the treatment, and effects on survival after relapse.
Baylor University basketball scandal – player Patrick Dennehy was murdered by teammate Carlton Dotson. Later, coach Dave Bliss instructed his players to lie to NCAA investigators that Dennehy dealt drugs. In the wake of these events, numerous violations of NCAA rules were discovered. Duke lacrosse case – a stripper hired by members of the Duke University men's lacrosse team for an informal team party in 2006 falsely accused three players of rape. University of North Carolina at Chapel Hill football scandal – over ten football players received improper benefits and committed academic fraud by turning in coursework prepared by tutors. 2011 University of Miami athletics scandal – Yahoo! Sports broke a story in which former Miami booster Nevin Shapiro, currently imprisoned for running a Ponzi scheme, indicated he had provided massive amounts of improper benefits to Miami players and coaches, mostly in football, but also in men's basketball. Penn State child sex abuse scandal – in November 2011, former Penn State defensive coordinator Jerry Sandusky was arrested on 40 counts of sexually abusing eight boys over a 15-year period including incidents in Penn State's football facilities. In June 2012, Sandusky was convicted on 45 charges related to the scandal. University of North Carolina academic-athletic scandal – in a follow-up to the UNC football scandal, new accusations of academic fraud arose in relation to the university's African and Afro-American Studies department and men's basketball program, men's football team, women's soccer and other sports as well.
==== Trypanosome resistance ==== After its introduction to the market in the 1980s, eflornithine has replaced melarsoprol as the first line medication against Human African trypanosomiasis (HAT) due to its reduced toxicity to the host. Trypanosoma brucei resistant to eflornithine was reported as early as the mid-1980s. The gene TbAAT6, conserved in the genome of Trypanosomes, is believed to be responsible for the transmembrane transporter that brings eflornithine into the cell. The loss of this gene due to specific mutations causes resistance to eflornithine in several trypanosomes. If eflornithine is prescribed to a patient with Human African trypanosomiasis caused by a trypanosome that contains a mutated or ineffective TbAAT6 gene, then the medication will be ineffective against the disease. Resistance to eflornithine has increased the use of melarsoprol despite its toxicity, which has been linked to the deaths of 5% of recipient HAT patients.
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.
Dry lyophilized powder is usually kept frozen, desiccated, and out of direct light. Sealed vials are not opened until needed, because moisture uptake can degrade short peptides. Longer archival storage is often done at lower temperatures than routine working stock.