The short version of actin binding fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2026-08-01. Anything still debated is marked as such rather than presented as settled.
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 synthetic peptide preparation marketed under a name derived from thymosin beta-4, a 43-residue actin-binding protein first isolated from thymus tissue. The full-length protein has a reported molecular mass near 4963 Da, while material sold as TB-500 is often described as a fragment containing the actin-binding motif LKKTETQ. Because suppliers use the name inconsistently, published sources sometimes refer to the same label as a fragment, a synthetic copy, or a related analog. This naming ambiguity complicates direct comparison of reports across studies.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Molecular mass | Approximately 4963 Da for full-length thymosin beta-4 | Value applies to the parent protein; fragment products may differ |
| Appearance | White to off-white lyophilized powder | Typical form of supplied synthetic peptide |
| Solubility | Freely soluble in water | Polar peptide; dissolves readily in aqueous buffer |
| Storage of dry powder | −20 °C, desiccated, protected from light | Standard laboratory practice for peptides |
| Typical detection method | Liquid chromatography–tandem mass spectrometry | Used in purity testing and anti-doping analysis |
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.
Peptide bonds are susceptible to hydrolysis under extreme pH and to enzymatic cleavage if proteases are present. Heat, oxidising agents, and prolonged exposure to light also contribute to loss of material. Aggregation can occur at high concentrations or in certain buffer systems, and it may not be visible to the eye. Storage at -20 C or below is typical for both powder and aliquoted solutions, and desiccation of the powder is preferred.
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.
Additionally, it was soon found that homopyrimidine and some purine-rich oligonucleotide are able form a stable H-DNA structure with the homopurine-homopyrimidine binding sequence-specific structures on the DNA duplexes.
== External links == Association des medecins rhumatologues du Quebec American College of Rheumatology European League Against Rheumatism Consortium of Rheumatology Researchers of North America, Inc. British Society for Rheumatology Canadian Rheumatology Association Association of Rheumatology Health Professionals (archived 3 March 2009) German Society for Rheumatology
=== International normalized ratio === The result (in seconds) for a prothrombin time performed on a normal individual will vary according to the type of analytical system employed. This is due to the variations between different types and batches of manufacturer's tissue factor used in the reagent to perform the test. The INR was devised to standardize the results. Each manufacturer assigns an ISI value (International Sensitivity Index) for any tissue factor they manufacture. The ISI value indicates how a particular batch of tissue factor compares to an international reference tissue factor. The ISI is usually between 0.94 and 1.4 for more sensitive and 2.0–3.0 for less sensitive thromboplastins. The INR is the ratio of a patient's prothrombin time to a normal (control) sample, raised to the power of the ISI value for the analytical system being used.
The first woman elected president of a country was Vigdís Finnbogadóttir of Iceland, who won the 1980 presidential election as well as three subsequent elections, remaining in office for a total of 16 years, which makes her the longest-serving non-hereditary female head of state in history. Vigdís was also the first woman to win a presidential election where the second place candidate was another woman: she defeated Sigrún Þorsteinsdóttir in the 1988 presidential election. The first democratically elected female prime minister of a Muslim majority country was Benazir Bhutto of Pakistan, who led her party to victory in the 1988 general election and later in 1993, making her the first woman democratically elected leader of any Muslim nation. Bhutto was also the first of only two non-hereditary female world leaders who gave birth to a child while serving in office, the other being Jacinda Ardern of New Zealand. The longest-tenured female non-hereditary head of government is Sheikh Hasina of Bangladesh. She served as the country's prime minister from June 1996 to July 2001 and again from January 2009 until August 2024, for a combined total of over 20 years. Finland was the first republic in which women served concurrently as both the head of state and head of government, with both Anneli Jäätteenmäki and Mari Kiviniemi serving as prime ministers under president Tarja Halonen.
=== EC 2.9: selenium transferases === EC 2.9 includes enzymes that transfer selenium-containing groups. This category only contains two transferases, and thus is one of the smallest categories of transferase. Selenocysteine synthase, which was first added to the classification system in 1999, converts seryl-tRNA(Sec UCA) into selenocysteyl-tRNA(Sec UCA).
Sources: en.wikipedia.org
Patients should be advised to remove any medicated patch prior to an MRI scan and replace it with a new patch after the scan is complete. In 2009, an article in Europace journal detailed stories of skin burns that occurred with transdermal patches that contain metal (usually as a backing material) caused by shock therapy from external as well as internal cardioverter defibrillators (ICD).
Most of these parameters cannot be determined quantitatively, at least during the early phases of a project. The best way to take advantage of a project portfolio is to develop and use it in an iterative way. By comparing the entries at regular intervals, for instance, every 3 months, the directions that the projects take can be visualized. If a negative trend persists with one particular project, the project should be put on the watch list.
== Interactions == Combination with selective serotonin reuptake inhibitors, serotonin–norepinephrine reuptake inhibitors, serotonin releasing agents, and serotonin receptor agonists may lead to potentially lethal serotonin syndrome. Combination with MAOIs may also result in an adrenergic storm. Use of tapentadol with alcohol or other central nervous system depressants such as benzodiazepines, barbiturates, nonbenzodiazepines, phenothiazines, gabapentinoids and other opiates may result in increased impairment, sedation, respiratory depression, and death. Tapentadol is partially metabolized by the hepatic enzymes CYP2C9, CYP2C19, and CYP2D6 so it innately has interactions with drugs that enhance or repress the activity/expression of one or more of these enzymes, as well as with substrates of these enzymes (due to competition for the enzyme); some enzyme mediators/substrates require dosing adjustments to one or both medications. The combination of tapentadol and alcohol may result in increased plasma concentrations of tapentadol and produce respiratory depression to a degree greater than the sum of the two drugs when administered separately; patients should be cautioned against alcohol consumption when taking tapentadol as the combination may be fatal. Tapentadol should be used with caution in patients who are taking one or more anticholinergic drugs, as this combination may result in urine retention (which can result in serious renal damage and is considered a medical emergency).
The FDA also expanded the intended use for the PD-L1 IHC 22C3 pharmDx kit to include use as a companion diagnostic device for selecting patients with head and neck squamous cell carcinoma for treatment with pembrolizumab as a single agent. In July 2019, the US FDA approved pembrolizumab for patients with recurrent, locally advanced or metastatic, squamous cell carcinoma of the esophagus (ESCC) whose tumors express PD-L1 (Combined Positive Score [CPS] ≥ 10), as determined by an FDA-approved test, with disease progression after one or more prior lines of systemic therapy. The FDA also approved a new use for the PD-L1 IHC 22C3 pharmDx kit as a companion diagnostic device for selecting patients for the above indication. In June 2020, the US FDA approved pembrolizumab as monotherapy for the treatment of adults and children with unresectable or metastatic tumor mutational burden-high (TMB-H) [≥ 10 mutations/megabase (mut/Mb)] solid tumors, as determined by an FDA-approved test, that have progressed following prior treatment and who have no satisfactory alternative treatment options. In March 2021, the accelerated approval indication in the US for the treatment of people with metastatic small-cell lung cancer (SCLC) was removed. In January 2024, the FDA approved pembrolizumab, in combination with chemoradiotherapy, for people with FIGO 2014 Stage III-IVA cervical cancer.
== History == Catalase was first noticed in 1818 by Louis Jacques Thénard, who discovered hydrogen peroxide (H2O2). Thénard suggested its breakdown was caused by an unknown substance. In 1900, Oscar Loew was the first to give it the name catalase, and found it in many plants and animals. In 1937 catalase from beef liver was crystallized by James B. Sumner and Alexander Dounce and the molecular weight was measured in 1938. The amino acid sequence of bovine catalase was determined in 1969, and the three-dimensional structure in 1981.
Sources: en.wikipedia.org
Virtually all staple foods come either directly from primary production by plants, or indirectly from animals that eat them. Plants and other photosynthetic organisms are at the base of most food chains because they use the energy from the sun and nutrients from the soil and atmosphere, converting them into a form that can be used by animals. This is what ecologists call the first trophic level. The modern forms of the major staple foods, such as hemp, teff, maize, rice, wheat and other cereal grasses, pulses, bananas and plantains, as well as hemp, flax and cotton grown for their fibres, are the outcome of prehistoric selection over thousands of years from among wild ancestral plants with the most desirable characteristics. Botanists study how plants produce food and how to increase yields, for example through plant breeding, making their work important to humanity's ability to feed the world and provide food security for future generations. Botanists also study weeds, which are a considerable problem in agriculture, and the biology and control of plant pathogens in agriculture and natural ecosystems. Ethnobotany is the study of the relationships between plants and people. When applied to the investigation of historical plant–people relationships ethnobotany may be referred to as archaeobotany or palaeoethnobotany.
Alternative methods of preservation, such as ice packing or laying the body on so called 'cooling boards', gradually lost ground to the increasingly popular and effective methods of embalming. By the mid-19th century, the newly emerging profession of businessmen-undertakers – who provided funeral and burial services – began adopting embalming methods as standard. Embalming became more common in the United States during the American Civil War, when servicemen often died far from home. The wish of families for their remains to be returned home for local burial and lengthy transport from the battlefield helped it become popular. The period from about 1861 is sometimes known as the funeral period of embalming and is marked by a separation of the fields of embalming by undertakers and embalming (anatomical wetting) for medical and scientific purposes. Dr Thomas Holmes received a commission from the Army Medical Corps to embalm the corpses of dead Union officers to return to their families. Military authorities also permitted private embalmers to work in military-controlled areas. The passage of Abraham Lincoln's body home for burial was made possible by embalming, and it brought wider public attention to the possibilities and potential of embalming. Until the early 20th century, embalming fluids often contained arsenic until it was supplanted by more effective and less toxic chemicals.
==== Role of the pancreas ==== In 1683, a surgical experiment by Johann Conrad Brunner almost led to a medical breakthrough. He excised the pancreas of a neighbour's hunting dog, causing polyuria and polydipsia. Brunner very clearly described these classic symptoms in pancreatectomized dogs, but made no association with diabetes. In 1788, Thomas Cawley published a case study in the London Medical Journal based on an autopsy of a diabetic patient. He observed stones and signs of tissue damage in the patient's pancreas, noting that the "right extremity of the pancreas was very hard, and appeared to be scirrhous." Considering the idea that diabetes "be not a disease of the kidneys", he suggested that "a cure may have been effected... provided the stomach and organs subservient to digestion had retained their digestive power". In the decades that followed, Richard Bright (1831) and Von Recklinhausen (1864) also reported gross changes in the pancreas of diabetic patients. Claude Bernard demonstrated the function of pancreatic juice in digestion between 1849 and 1856, clarifying an important link in the pathophysiology of diabetes.
== Allergy == Vicilins are a significant class of allergen found in legumes. The IgE binding proteins found were closely related and belonged to the 7S globulin family of seed storage proteins, which helped identify the allergen. Cross-reactions with various legumes are common when Pis s 1 and vicilins are combined in other seeds.
Sources: en.wikipedia.org
Not necessarily. TB-500 is a commercial label that suppliers apply to synthetic peptides described as thymosin beta-4 or a fragment of it. Published research most often studies the full-length protein, so statements about one do not automatically transfer to the other.
No. No major regulatory authority lists an approved product under this name, and no pharmacopoeial monograph exists for it. Material sold under the label is therefore supplied outside approved pharmaceutical channels, which affects the quality documentation available.
It falls within a prohibited class covering peptide hormones and growth factors, based on presumed effects on tissue repair and blood vessel formation. Anti-doping laboratories have published mass spectrometry methods for detecting thymosin beta-4 related peptides in urine samples.
Desiccated storage at −20 °C is conventional, with −80 °C for extended periods. Vials should be warmed to room temperature before opening to prevent condensation on the powder.