A practical reference on counter-ion: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
Reviewed 2026-06-21. Anything still debated is marked as such rather than presented as settled.
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.
| Property | Value | Notes |
|---|---|---|
| Physical form | Lyophilised powder | Sealed vial; reconstituted before laboratory use |
| Appearance | White to off-white solid | Visual descriptor used on certificates of analysis |
| Solubility class | Water-soluble | Dissolves in water and aqueous buffers |
| Reported mass, fragment | Near 889 Da | Value depends on the stated sequence |
| Reported mass, parent protein | Near 4963 Da | 43-residue thymosin beta-4 |
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.
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.
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.
Controlled human trials of the short fragment are scarce. Much of what appears in review articles is extrapolated from animal models or from studies of the parent protein, and literature searches return a larger body of cardiac and ophthalmic work on thymosin beta-4 than on the abbreviated peptide. Regulatory treatment differs by jurisdiction, and in several countries the material is handled as a research chemical rather than an approved therapeutic. Statements about human benefit should be read as provisional.
Biological interest in this peptide centers on its relationship to actin dynamics. Thymosin beta-4 binds monomeric actin through an LKKTET motif, and a short sequence carrying that motif can compete with other actin-binding proteins in cell-free preparations. Investigators propose that such competition shifts the balance between filament assembly and disassembly, which in turn affects how readily a cell extends protrusions and migrates. Most of the supporting observations come from cultured cells and purified protein systems rather than from intact organisms.
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.
==== Indications ==== Nabiximol, sold under the trade name Sativex®, is a natural mixture of tetrahydrocannabinol (THC) and cannabidiol (CBD) in a 1:1 ratio. Although not approved in the United States, Nabiximol is approved in some European countries as well as Canada for use as an buccal spray for symptomatic relief of spasticity and neuropathic pain in multiple sclerosis (MS). Different reviews were conducted to examine the effects of nabiximol on spasticity in multiple sclerosis, but their results were inconsistent. As some systemic reviews concluded that nabiximols is efficient in refractory spasticity of multiple sclerosis not responsive to other standard treatment, it may be considered as an adjuvant therapy to the standard therapy.
=== Public engagement === Olabisi works with Mae Jemison on the grant project 100 Year Starship, an interdisciplinary initiative that is exploring the technologies necessary to achieve interstellar travel, with the goal that all such technologies would improve life on Earth (e.g., better power sources, clean energy, clothing that doesn't need washing). She presented the program and how it intersected with her work at the European Parliament in 2013. In 2016, she featured in a Vanity Fair and IBM collaboration celebrating women in science. In 2019, she was interviewed by Forbes.
Nuclear warfare, also known as atomic warfare, is a military conflict or prepared political strategy that deploys nuclear weaponry. Nuclear weapons are weapons of mass destruction; in contrast to conventional warfare, nuclear warfare can produce significantly more destruction in a much shorter time and can have a long-lasting radiological result. A large nuclear exchange would kill hundreds of millions of people. It would have long-term effects, from the fallout released, and could also lead to secondary effects, such as nuclear winter, nuclear famine, and societal collapse. A global nuclear war with current national stockpiles may lead to various devastating scenarios, including human extinction. As of 2026, the first and only use of nuclear weapons in armed conflict was the United States atomic bombings of Hiroshima and Nagasaki, on August 6 and 9, 1945, in the final days of World War II. The two bombings resulted in the deaths of between 150,000 and 246,000 people. A debate continues over ethical, legal, and military aspects of the bombings, including their role in the surrender of Japan. The Cold War prompted the nuclear arms race. Nuclear weapons were later developed by the Soviet Union (1949), the United Kingdom (1952), France (1960), and China (1964). In 1974, India, and in 1998, Pakistan, with a history of conflict, developed nuclear weapons. Israel (1960s) and North Korea (2006) also developed nuclear weapons.
Hood's research group corrected the neurological defect in mice (the shiverer defect) by transferring a normal MBP gene into the fertilized egg of the shiverer mouse. These discoveries led to extensive studies of MBP and its biology.
Both carboxamides and aldoximes can be dehydrated using aluminum chloride and sodium iodide in acetonitrile. Likewise, both classes can be dehydrated with oxalyl chloride and catalytic dimethyl sulfoxide in a reaction analogous to the Swern oxidation. Conversion to nitriles under catalysis by heptavalent rhenium species (perrhenic acid or trimethylsilyl perrhenate) is effective for both amides and aldoximes; the water formed can be removed by azeotropic distillation. The conversion of aldehydes to nitriles via aldoximes is a popular laboratory route. Aldehydes react readily with hydroxylamine salts, sometimes at temperatures as low as ambient, to give aldoximes. These can be dehydrated to nitriles by simple heating, although a wide range of reagents may assist with this, including triethylamine/sulfur dioxide, zeolites, or sulfuryl chloride. The related hydroxylamine-O-sulfonic acid reacts similarly.
Sources: en.wikipedia.org
== Algorithm == The Chou–Fasman method predicts helices and strands in a similar fashion, first searching linearly through the sequence for a "nucleation" region of high helix or strand probability and then extending the region until a subsequent four-residue window carries a probability of less than 1. As originally described, four out of any six contiguous amino acids were sufficient to nucleate helix, and three out of any contiguous five were sufficient for a sheet. The probability thresholds for helix and strand nucleations are constant but not necessarily equal; originally 1.03 was set as the helix cutoff and 1.00 for the strand cutoff. Turns are also evaluated in four-residue windows, but are calculated using a multi-step procedure because many turn regions contain amino acids that could also appear in helix or sheet regions. Four-residue turns also have their own characteristic amino acids; proline and glycine are both common in turns. A turn is predicted only if the turn probability is greater than the helix or sheet probabilities and a probability value based on the positions of particular amino acids in the turn exceeds a predetermined threshold. The turn probability p(t) is determined as:
The British implemented a scorched earth policy under which they targeted everything within the controlled areas that could give sustenance to the guerrillas, making it harder for them to survive. As British troops swept the countryside, they systematically destroyed crops, poisoned wells, burned homesteads and farms, and interned Boer and African men, women, children and workers in concentration camps. The British established mounted raiding columns in support of sweeper columns. These were used to rapidly follow and relentlessly harass the Boers to delay them and cut off escape, while the sweeper units caught up. Many of the 90 or so mobile columns formed by the British to participate in such drives were a mixture of British and colonial troops, but they also had a large minority of armed Africans. The number of armed Africans serving with these columns has been estimated at 20,000. The British Army made use of Boer auxiliaries who had been persuaded to change sides and enlist as "National Scouts". Serving under General Andries Cronjé (1849–1923), the National Scouts were despised as joiners but numbered a fifth of the fighting Afrikaners by the end of the War. The British utilised armoured trains to deliver rapid reaction forces much more quickly to incidents (such as Boer attacks on blockhouses and columns) or drop them off ahead of retreating Boer columns.
Nostoc punctiforme is a species of filamentous cyanobacterium. Under non-limiting nutritional environmental conditions, its filaments are composed of photosynthetic vegetative cells; upon nutrient limitation, some of these cells undergo differentiation into heterocysts, akinetes or hormogonia. N. punctiforme is one of the Nostoc strains able to maintain diazotrophic symbiosis with higher plants such as the bryophytes Anthocerus punctatus and Blasia pusilla, water ferns from the genus Azolla, the cycads Macrozamia spp., and the angiosperm Gunnera.
== Etymology and history == From the Greek words baeo (little) and kystis (bladder) 1945 P. baeocystis is first collected in Eugene, Oregon. 1958 P. baeocystis is formally described and published by Singer and Smith. 1962 Psilocin is first reported in this species. 1967-68 Baeocystin and norbaeocystin are discovered and named. 1981 Testing again reveals psilocybin, psilocin, baeocystin and norbaeocystin.
Sources: en.wikipedia.org
== Mechanism of action == After the venom has entered the body via the wasp sting, it enters the bloodstream, where it will be diluted in the blood and distributed through the organism. Pompilidotoxins target the sodium channels, so the toxin reaches its target sites via the distribution by the bloodstream. Research by Sahara et.al. (2000) has suggested that α-PMTX might slow or block the conformational changes that are necessary for the fast inactivation of voltage gated sodium channels. This causes the intracellular sodium concentration to increase. They hypothesise that this effect could be caused by the α-PMTX binding to similar elements of the neurotoxin receptor site 3 on the extracellular surface of the sodium channel. α-PMTX also enhances both the inhibitory postsynaptic potentials (IPSPs) and the excitatory postsynaptic potentials (EPSPs). The eventual paralysis of the spider is caused by the prolonged membrane depolarization, which is induced by the EPSPs. However, when the fast inactivation is slowed or blocked by channel blocker like PMTX, the membrane will not repolarize properly, but stay in a depolarized state instead. The long-lasting depolarisation leads to paralysis. A study by Konno et.al. (2001) has found that the positively charged amino acids in β-PMTX likely bind to the Glu-1616 site on the D4S3-S4 loop of the sodium channel. This indicates that the positive charges of PMTXs are a crucial part of the toxins, as they are likely involved in the electrostatic bonding between the toxin and the sodium channel.
==== Acute myocardial infarction ==== Beta blockers are indicated for the treatment of acute myocardial infarctions. During a myocardial infarction, systemic stress causes an increase in circulating catecholamines. This results an increase in heart rate and blood pressure, therefore increasing myocardial oxygen demand. Beta blockers competitively inhibit catecholamines acting on the β1-adrenergic receptors, thus reducing these detrimental effects and resulting in reduced myocardial oxygen consumption and demand. A 2019 Cochrane review compared beta blockers with placebo or no intervention, it found that beta blockers probably reduced the short-term risk of reinfarction and the long-term risk of all-cause mortality and cardiovascular mortality. The review identified that beta blockers likely had little to no impact on short-term all-cause mortality and cardiovascular mortality.
It found ceftolozane/tazobactam to be at least as effective as meropenem: the infection had resolved in 54% of participants (197 out of 362) after 7 to 14 days of treatment with ceftolozane/tazobactam compared with 53% of participants (194 out of 362) on meropenem.
The water then traveled through the channels into sixteen fountains known as the "stairway of fountains", reserving the first water source for the Emperor. This incredible feat supplied the population of Machu Picchu, which varied between 300 and 1000 people when the emperor was present and also helped irrigate water to the farming steppes. The fountains and canal system were built so well that they would, after a few minor repairs, still work today. To go along with the Incas' advanced water supply system, an equally impressive drainage system was built as well. Machu Picchu contains nearly 130 outlets in the center that moved the water out of the city through walls and other structures. The agriculture terraces are a feature of the complicated drainage system; the steppes helped avoid erosion and were built on a slope to aim excess water into channels that ran alongside the stairways. These channels carried the runoff into the main drain, avoiding the main water supply. This carefully planned drainage system shows the Incas' concern and appreciation for clean water. Water engineer Ken Wright and his archaeological team found the emperor’s bathing room complete with a separate drain that carried off his used bath water so it would never re-enter Machu Picchu’s water supply.
Applications of this method include the analysis of fragile molecules and guest-host interactions that cannot be studied using regular electrospray ionization. Electrospray ionization has also been achieved at pressures as low as 25 torr and termed subambient pressure ionization with nanoelectrospray (SPIN) based upon a two-stage ion funnel interface developed by Richard D. Smith and coworkers. The SPIN implementation provided increased sensitivity due to the use of ion funnels that helped confine and transfer ions to the lower pressure region of the mass spectrometer. Nanoelectrospray emitter is made out of a fine capillary with a small aperture about 1–3 micrometer. For sufficient conductivity this capillary is usually sputter-coated with conductive material, e.g. gold. Nanoelectrospray ionization consumes only a few microliters of a sample and forms smaller droplets. Operation at low pressure was particularly effective for low flow rates where the smaller electrospray droplet size allowed effective desolvation and ion formation to be achieved. As a result, the researchers were later able to demonstrate achieving an excess of 50% overall ionization utilization efficiency for transfer of ions from the liquid phase, into the gas phase as ions, and through the dual ion funnel interface to the mass spectrometer.
Sources: en.wikipedia.org
No. TB-500 is a trade-style label used for a synthetic peptide described as a fragment of thymosin beta-4, while thymosin beta-4 is the full 43-residue protein. The two differ in size and are not interchangeable terms in analytical work.
Naming for research peptides is not standardised, and suppliers sometimes apply the same label to different chain lengths. Certificates of analysis and mass data are the practical way to determine what a given lot contains.
The fragment commonly cited under this label is reported near 889 Da, and the parent protein near 4963 Da. Reported values shift with the exact sequence and with residual counter-ions or water in the sample.
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.