actin-binding motif is one of those subjects where the details matter more than the headlines. This page pulls together the background, the mechanisms, and the practical points readers ask about most.
Last reviewed on 2026-08-01. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
Research peptides are typically supplied as a white to off-white lyophilised powder in a sealed vial. The dry solid is more stable than a solution and is normally kept refrigerated or frozen until use. Dissolution is usually done in water, phosphate-buffered saline or a similar aqueous medium, depending on the assay. Because the material is hygroscopic and easily contaminated, opening vials in a low-humidity environment and recording the lot number before use are standard laboratory practices.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Typical form | Lyophilised powder | Reconstituted before use |
| Storage temperature, dry | -20 °C or below | Desiccated, protected from light |
| Purity determination | Reversed-phase HPLC | Reported as percentage of total peak area |
| Identity confirmation | Mass spectrometry | ESI or MALDI-TOF versus calculated mass |
| Common synonyms | Tβ4 fragment; thymosin beta-4 fragment | Naming varies between suppliers |
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.
Research interest in thymosin beta-4 fragments centres on actin sequestration, cell migration and tissue repair models. Most published work uses cultured cells or animal wound and cardiac preparations, and findings are generally described as preliminary. No fragment of this protein has been approved as a therapeutic product by major regulators. Reviews of the field note inconsistent dosing, delivery routes and outcome measures across studies, which complicates direct comparison. The material is best understood as a laboratory reagent with an active but unresolved research literature.
TB-500 is a catalogue name applied to a synthetic peptide related to thymosin beta-4, an actin-binding protein found in most mammalian cells. Suppliers do not use the label consistently: some describe it as the full 43-residue protein, others as a short fragment from the actin-binding region, and others as a related tetrapeptide. Because the name is commercial rather than chemical, two products sold under it may not contain the same molecule. This naming ambiguity is the first point to check in any description of the material.
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.
Literature and online discussion often conflate TB-500 with full-length thymosin beta-4, even though the two differ in size and are not interchangeable in analytical terms. The fragment is produced by solid-phase peptide synthesis, and the product is a defined seven-residue chain rather than a biological extract. Because the term is a trade-style label, two vendors may supply materials of the same nominal sequence but different counter-ion content, purity, or water content. Comparisons across studies are therefore difficult unless the exact sequence and purity are reported.
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.
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.
=== Awards === Counter-Strike earned numerous accolades on its release. In 2000, it was recognized by many gaming magazines and websites as Game of the Year, Action Game of the Year, or Online Game of the Year. The game also won 2 reader polls for Game of the Year from GameSpot US and VoodooExtreme readers. At the Game Developer 2001 Spotlight Awards, Counter-Strike was named Best Multiplayer Game and received a Special Achievement in Gaming. In 2003, Counter-Strike was inducted into GameSpot's greatest games of all-time list.
Earth The HIC of mantle rocks on Earth is highly variable; and that of mantle water is around −80‰ ~ −50‰ depending on its states such as fluid, hydrous phase, hydroxyl point defect, juvenile water (from degassing of the mantle), magmatic water (water equilibrated with a magma). Sun The Sun's DHR is around 21 ± 5 × 10−6. Mars The current HIC is enriched by a factor of 5 relative to Earth's seawater due to continual losses of H in Martian atmosphere. Therefore, the δD is estimated at around +4000‰. The DHRs of Jupiter and Saturn are nearly in the order of 10−5, and the DHRs of Uranus and Neptune are closer to 10−4. Hydrogen is the most abundant element in the universe. Variations in isotopic composition of extraterrestrial materials stem from planetary accretion or other planetary processes such as atmospheric escape, and are larger for H and N than for C and O. The preservation of D-enrichment is observed in chondritic meteorites, interplanetary dust particles and cometary Volatiles. From the helium isotope abundance data, the cosmic DHR is estimated at around 20 ppm: much lower than the terrestrial DHR of 150 ppm. The enrichment of D/H from the proto-solar reservoir occurs for most of the planets except for Jupiter and Saturn, the massive gaseous planets. The DHRs of the atmospheres of Venus and Mars are ~2 × 10−2 and ~8 × 10−4 respectively. The DHRs of Uranus and Neptune are larger than that of protosolar reservoir by a factor of ~3 due to their deuterium-rich icy cores.
Protein structure is dynamic; the protein hemoglobin bends into slightly different forms as it facilitates the capture, transport, and release of oxygen molecules within mammalian blood. A single nucleotide difference within DNA can cause a change in the amino acid sequence of a protein. Because protein structures are the result of their amino acid sequences, some changes can dramatically change the properties of a protein by destabilizing the structure or changing the surface of the protein in a way that changes its interaction with other proteins and molecules. For example, sickle-cell anemia is a human genetic disease that results from a single base difference within the coding region for the β-globin section of hemoglobin, causing a single amino acid change that changes hemoglobin's physical properties. Sickle-cell versions of hemoglobin stick to themselves, stacking to form fibers that distort the shape of red blood cells carrying the protein. These sickle-shaped cells no longer flow smoothly through blood vessels, having a tendency to clog or degrade, causing the medical problems associated with this disease. Some DNA sequences are transcribed into RNA but are not translated into protein products—such RNA molecules are called non-coding RNA. In some cases, these products fold into structures which are involved in critical cell functions (e.g. ribosomal RNA and transfer RNA). RNA can also have regulatory effects through hybridization interactions with other RNA molecules (such as microRNA).
=== Tunable resistive pulse sensing === Tunable resistive pulse sensing (TRPS) is a single-particle analytical technique used to measure the size, concentration, and charge of nano and micro-sized particles by detecting a change in ionic current. The passage of an individual particle through a charged nanopore creates a transient change in resistance and subsequent decrease in the background current, known as a blockade event. Blockade characteristics are representative of particle and sample properties: blockade magnitude is proportional to particle size, the blockade rate is directly related to particle concentration, and the speed with which a particle moves through the pore is related to its zeta potential.
Sources: en.wikipedia.org
Casualty numbers have escalated significantly over time. According to a Stratfor report, the number of drug-related deaths in 2006 and 2007 (2,119 and 2,275) more than doubled to 5,207 in 2008. The number further increased substantially over the next two years, from 6,598 in 2009 to over 11,000 in 2010. According to data from the Mexican government, the death numbers are even higher: 9,616 in 2009, 15,273 in 2010, coming to a total of 47,515 killings between 2006 and January 2012. It is often not clear what deaths are part of the Mexican drug war versus general criminal homicides, and different sources give different estimates. Casualties are often measured indirectly by estimated total deaths from organized crime in Mexico. This amounts to about 115,000 people in the years 2007–2018. From 2018 to 2020, it was estimated that there were 11,400 reports of gang violence, and over 80% of the attacks targeted civilians, resulting in 13,000 related deaths during the period.
H–D exchange has been used to characterize protein structures and protein–protein interactions. The exchange reaction needs to be carried out with the isolated proteins and with the complex. The exchanging regions are then compared. If a region is buried by the binding, the amides in this region may be protected in the complex and exchange slowly. However, one must bear in mind that H–D exchange cannot be used to locate binding interfaces for all protein-protein interactions. Some protein-protein interactions are driven by electrostatic forces of side chains and are unlikely to change the exchange rate of backbone amide hydrogens, particularly if the amide hydrogens are located in stable structural elements such as alpha helices. Lastly, H–D exchange can be used to monitor conformational changes in proteins as they relate to protein function. If conformation is altered as result of post-translational modification, enzyme activation, drug binding or other functional events, there will likely be a change to H/D exchange that can be detected.
== Medical uses == Vericiguat is indicated to reduce the risk of cardiovascular death and hospitalization for heart failure following a prior hospitalization for heart failure or need for outpatient intravenous diuretics, in adults with symptomatic chronic heart failure and an ejection fraction of less than 45% (HFrEF). Vericiguat is usually given orally once every day with food. No dose adjustments are required in the elderly, in people with mild-to-moderate liver failure, or in those with impaired kidney function. As of 2024, no studies have found information for patients with severely impaired kidney function, severe liver failure, or are on dialysis. Vericiguat is contraindicated in pregnancy. While there are no studies on its safety when used by pregnant women, animals studies suggest higher rates of birth defects, as well as increased number of abortions and resorptions. It may also pass into breast milk, but the effects on breastfed infants is unknown. The manufacturer advises that child-bearing age patients should be on contraception and assessed for pregnancy before starting treatment.
If this is the case, similarity in lifetimes of intermediate daughters becomes a meaningless argument, as different isomers of the same nuclide can have different half-lives: for example, the ground state of 180Ta has a half-life of hours, but an excited state 180mTa has never been observed to decay. This study found reason to doubt and criticise the IUPAC approval of the discoveries of elements 115 and 117, but the data from Riken for element 113 was found to be congruent, and the data from the JINR team for elements 115 and 113 to probably be so, thus endorsing the IUPAC approval of the discovery of element 113. Two members of the JINR team published a journal article rebutting these criticisms against the congruence of their data on elements 113, 115, and 117 in June 2017.
In January 2021, Taco Bell announced the return of potatoes to the menu after a brief discontinuation in August 2020 in efforts to streamline processes in their restaurants in response to the COVID-19 pandemic. In addition to the potatoes, the company had announced plans to expand their vegetarian menu by introducing Beyond Meat as a plant-based vegetarian customization option. In April 2021, Taco Bell said that it would start reusing hot sauce packets in partnership with the recycling company TerraCycle, aiming to reduce the environmental pollution. In August 2021, Taco Bell announced the Crispy Chicken Sandwich Taco. On January 6, 2022, Taco Bell launched a digital taco subscription service called the Taco Lover's Pass through the company app. For the cost of $10, a customer can order one of seven different tacos each day for 30 consecutive days. On April 18, 2022, Taco Bell announced that Mexican Pizza would return to its menu on May 19, after its having previously been discontinued in November 2020. From July to August 2022, filmmaker Sam Reid ate nothing but Taco Bell for 30 days, testing the nutritional content of the food in a similar vein to Super Size Me. The stunt gained widespread national attention for both Sam and the fast food chain, including multiple news stations covering his diet and a mention by Jimmy Fallon on The Tonight Show. Reid published a documentary about the challenge on his YouTube channel in October the same year.
Sources: en.wikipedia.org
During the First World War (1914–1918), and for a short period afterwards, there were at least 250 recognised airfields in France that the Royal Flying Corps, Royal Naval Air Service, and Royal Air Force used at various times.
In theory, many cancers might be prevented in this way, since an excess of thyroid cancer, presumably due to radioiodine uptake, is the only proven long-term effect after exposure of a population to radioactive fission products from a reactor accident or atomic bomb fallout. Taking large amounts of iodide saturates thyroid receptors and prevents uptake of most radioactive iodine-131 that may be present from fission product exposure (although it does not protect from other radioisotopes, nor from any external radiation). The protective effect of KI lasts approximately 24 hours, so must be dosed daily until a risk of significant exposure to this isotope no longer exists; as it decays relatively rapidly with a half-life of eight days (other iodine isotopes of concern are even shorter-lived), 99.95% of the radioiodine has vanished after three months.
The residence time of a fluid parcel is the total time that the parcel has spent inside a control volume (e.g.: a chemical reactor, a lake, a human body). The residence time of a set of parcels is quantified in terms of the frequency distribution of the residence time in the set, which is known as residence time distribution (RTD), or in terms of its average, known as mean residence time. Residence time plays an important role in chemistry and especially in environmental science and pharmacology. Under the name lead time or waiting time it plays a central role respectively in supply chain management and queueing theory, where the material that flows is usually discrete instead of continuous.
The source of ADP-ribose for most enzymes that perform this modification is the redox cofactor NAD+. In this transfer reaction, the N-glycosidic bond of NAD+ that bridges the ADP-ribose molecule and the nicotinamide group is cleaved, followed by nucleophilic attack by the target amino acid side chain. (ADP-ribosyl)transferases can perform two types of modifications: mono(ADP-ribosyl)ation and poly(ADP-ribosyl)ation.
== Mechanism of action == Isoniazid is a prodrug that inhibits the formation of the mycobacterial cell wall. Isoniazid must be activated by KatG, a bacterial catalase-peroxidase enzyme in Mycobacterium tuberculosis. KatG catalyzes the formation of the isonicotinic acyl radical, which spontaneously couples with NADH to form the nicotinoyl-NAD adduct. This complex binds tightly to the enoyl-acyl carrier protein reductase InhA, thereby blocking the natural enoyl-AcpM substrate and the action of fatty acid synthase. This process inhibits the synthesis of mycolic acids, which are required components of the mycobacterial cell wall. A range of radicals are produced by KatG activation of isoniazid, including nitric oxide, which has also been shown to be important in the action of another antimycobacterial prodrug pretomanid.
Sources: en.wikipedia.org
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.
Synthesis routes, purification steps and the analytical method used all affect the reported figure. A purity number is only comparable when the chromatographic conditions and detection wavelength are stated.
It reports what the supplier measured on a sample, which is useful but not absolute. Independent mass confirmation on the received lot is the more reliable check.
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.