Everything below concerns heptapeptide. We keep the language plain, cite what the science says, and separate well-supported claims from open questions.
Updated 2026-07-26. Numbers and descriptions here follow the published literature rather than marketing 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.
Thymosin beta-4 is a naturally occurring protein of 43 amino acids found in most mammalian cells, where it binds actin monomers and influences filament dynamics. It was first isolated from thymus tissue in the early 1980s, and its actin-binding activity was later mapped to a short region near the N-terminus. The synthetic fragment sold as TB-500 was designed to reproduce that region rather than the full protein. Whether a short fragment reproduces the behavior of the intact molecule remains an open question, since the parent protein carries additional structural elements outside the binding region.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Reported sequence | Ac-LKKTETQ | Described in most listings as the actin-binding region of thymosin beta-4 |
| Reported molecular weight | Approximately 889 Da | Value shifts with the stated sequence; compare against the certificate of analysis |
| Parent protein length | 43 amino acids | Thymosin beta-4; the fragment covers only a small part of it |
| Common synonyms | TB4 fragment; thymosin beta-4 fragment | Trade-style names rather than formal nomenclature |
| Formal monographs | Not established | Labeling conventions differ by supplier and region |
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.
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.
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.
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.
(1990); "Copper-Catalyzed Amino Acid Condensation in Water - A Simple Possible Way of Prebiotic Peptide Formation"; Origins Life Evol. Biosphere 1990, 20(5), pp. 401–410. DOI: 10.1007/BF01808134. Schwendinger, M. G.; Rode, Bend M.(1998); "Possible Role of Copper and Sodium Chloride in Prebiotic Evolution of Peptides"; Anal. Sci. 1989, 5(4), pp. 411–414. DOI: 10.2116/analsci.5.411. Plankensteiner, Kristof; Reiner, Hannes; Schranz, Benjamin; Rode, Bernd M. (2004); "Prebiotic formation of amino acids in a neutral atmosphere by electric discharge"; Angew. Chem. Int. Ed. 2004, 43, pp. 1886–1888. [1] Fitz, Daniel; Reiner, Hannes; Rode, Bernd M. (2007); "Chemical evolution toward the origin of life"]; Pure Appl. Chem. 2007, 79(12), pp. 2101–2117. DOI: 10.1351/pac200779122101. Fitz, Daniel; Jakschitz, Thomas; Rode, Bernd M. (2011); "Salt-Induced Peptide Formation in Chemical Evolution: Building Blocks Before RNA - Potential of Peptide Splicing Reactions"; In: Origins of Life: The Primal Self-Organization, Egel, Richard; Lankenau, Dirk-Henner; Mulkidjanian, Armen Y. (Eds.), ISBN 978-3-642-21624-4, Springer, Heidelberg, Berlin 2011, pp. 109–127. Jakschitz, Thomas A.; Rode, Bernd M. (2012); "Chemical Evolution from simple inorganic compounds to chiral peptides"; Chem. Soc. Rev. 2012, 41(16), pp. 5484–5489. DOI: 10.1039/C2CS35073D. Rode, Bernd M.; Plankensteiner, Kristof (2013); "Prebiotic Peptides"; In: Handbook of Biologically Active Peptides, Second Edition, Abba J. Kastin (Eds.), ISBN 978-012-3850959, Elsevier, Amsterdam 2013, pp. 1899–1903.
=== Two-step mechanism – autocatalysis model === In 1997, Finke and Watzky proposed a new kinetic model for the nucleation and growth of nanoparticles. This 2-step model suggested that constant slow nucleation (occurring far from supersaturation) is followed by autocatalytic growth where dispersity of nanoparticles is largely determined. This F-W (Finke-Watzky) 2-step model provides a firmer mechanistic basis for the design of nanoparticles with a focus on size, shape, and dispersity control. The model was later expanded to a 3-step and two 4-step models between 2004 and 2008. Here, an additional step was included to account for small particle aggregation, where two smaller particles could aggregate to form a larger particle. Next, a fourth step (another autocatalytic step) was added to account for a small particle agglomerating with a larger particle. Finally in 2014, an alternative fourth step was considered that accounted for a atomistic surface growth on a large particle.
The Humr are one of the tribes in the Baggara ethnic group, native to southwestern Kordofan in Sudan who speak Shuwa (Chadian Arabic), make a non-alcoholic drink from the liver and bone marrow of the giraffe, which they call umm nyolokh. They claim it is intoxicating (Arabic سكران sakran), causing dreams and even waking hallucinations. Anthropologist Ian Cunnison accompanied the Humr on one of their giraffe-hunting expeditions in the late 1950s, and noted that:
mole (mol) A unit (symbol: mol) used to measure the amount of a substance in terms of the absolute number of particles or entities composing the substance. By definition, one mole of any substance contains exactly the Avogadro number (i.e. 6.022×1023) of particles or entities.
Sources: en.wikipedia.org
In February 2015, Labcorp acquired Covance for $6.1 billion. In October 2015, Labcorp acquired Safe Foods International Holdings and its two operating companies, International Food Network and The National Food Laboratory, expanding its capabilities in food and beverage product-development and product-integrity. In March 2016, Labcorp acquired Pathology Inc., a provider of reproductive donor testing as well as anatomic, molecular and digital pathology services focused on women's health. In September 2016, Labcorp acquired Sequenom for $371 million including debt, expanding its operations in Europe and Asia. In October 2016, Labcorp acquired ClearPath Diagnostics, a provider of laboratory diagnostic services in the Northeastern United States, from Shore Capital Partners. In May 2017, Labcorp acquired Pathology Associates Medical Laboratories from Providence Health & Services and Catholic Health Initiatives. In September 2017, Labcorp acquired Chiltern, a contract research organization (CRO), for $1.2 billion, and contributed it to Covance. In 2019, Labcorp acquired Wellness Corporate Solutions, a workplace wellness company.
=== Legal status === In the United States, the main drug control agency, the Drug Enforcement Administration, reports an increase in annual aggregate production quotas of hydromorphone from 766 kilograms (1,689 pounds) in 1998 to 3,300 kilograms (7,300 lb) in 2006, and an increase in prescriptions in this time of 289%, from about 470,000 to 1,830,000. The 2013 production quota was 5,968 kilograms (13,157 lb). Like all opioids used for analgesia, hydromorphone is potentially habit-forming and is listed in Schedule II of the United States Controlled Substances Act of 1970 as well as in similar levels under the drugs laws of practically all other countries and it is listed in the Single Convention On Narcotic Drugs. The DEA ACSCN for hydromorphone is 9150. Hydromorphone is listed under the German Betäubungsmittelgesetz as a Betäubungsmittel in the most restricted schedule for medicinal drugs; it is controlled similarly in Austria (Suchtgift) under the SMG and the Swiss BetmG. The Misuse of Drugs Act 1971 (United Kingdom) and comparable French, Canadian, Australian, Italian, Czech, Croatian, Slovenian, Swedish, Polish, Spanish, Greek, Russian, and other laws similarly control it, as do regulations in virtually all other countries.
== Mechanism of action == Nalfurafine is an orally active, centrally acting, highly potent, selective full agonist of the κ-opioid receptor (KOR) (Ki = 75 pM; EC50 = 25 pM). As touched on above, nalfurafine shows atypical properties as a KOR agonist relative to other drugs. Notably, it does not completely substitute for the prototypical KOR agonist U-50488 in rodents, indicating qualitative differences in the discriminative effects of the two compounds. Moreover, unlike U-50488, it produces neither conditioned place aversion or preference in rodents. The drug is a 4,5-epoxymorphinan derivative, and is structurally unique relative to other KOR agonists. Nalfurafine may be a biased agonist of the KOR or a KOR subtype-selective agonist. Indeed, it has been found to act as a biased agonist of the KOR, preferring activation of β-arrestin signaling in vitro, but paradoxically, β-arrestin appears to be responsible for KOR agonist-induced aversion, and nalfurafine furthermore shows paradoxical effects in vivo that are not consistent with its in vitro profile. As such, more research is needed to clarify the distinct mechanisms and effects of this drug. Nalfurafine has been found in vitro to bind to the μ-opioid receptor and to possess weak partial agonist activity at this site, albeit with much lower affinity relative to the KOR. However, in vivo, nalfurafine has shown no indications of MOR agonism or antagonism in animals or humans, including no evidence of rewarding or reinforcing effects or physical dependence.
== History == The facility was created by 2014, with funding from the Canada Foundation for Innovation and the Ontario Research Fund. It is located in the University of Ottawa's Advanced Research Complex. It replaced the IsoTrace facility at the University of Toronto and cost around 10 million dollars. In 2017, the laboratory will host the 14th annual Accelerator Mass Spectrometry conference.
In medicine, Aschoff bodies are nodules found in the hearts of individuals with rheumatic fever. They result from inflammation in the heart muscle and are characteristic of rheumatic heart disease. These nodules were discovered independently by Ludwig Aschoff and Paul Rudolf Geipel, and for this reason they are occasionally called Aschoff–Geipel bodies.
Sources: en.wikipedia.org
They are either commercially available or easily synthesized, They have high acidity (pKa ~ 4) allowing for facile in situ deprotonation, The metal-carboxylate bond formation is reversible, facilitating the formation of well-ordered crystalline MOFs, and The bridging bidentate coordination ability of carboxylate groups favors the high degree of framework connectivity and strong metal-ligand bonds necessary to maintain MOF architecture under the conditions required to evacuate the solvent from the pores. The most common transition metals employed in carboxylate-based frameworks are Cu2+ and Zn2+. Lighter main-group metal ions have also been explored. Be12(OH)12(btb)4, the first successfully synthesized and structurally characterized MOF consisting of a light main group metal ion, shows high hydrogen storage capacity, but it is too toxic to be employed practically. There is considerable effort being put forth in developing MOFs composed of other light main group metal ions, such as magnesium in Mg4(bdc)3. The following is a list of several MOFs that are considered to have the best properties for hydrogen storage as of May 2012 (in order of decreasing hydrogen storage capacity). While each MOF described has its advantages, none of these MOFs reach all of the standards set by the U.S. DOE. Therefore, it is not yet known whether materials with high surface areas, small pores, or di- or trivalent metal clusters produce the most favorable MOFs for hydrogen storage.
== Origin == The genetic code is a key part of the history of life. Under the RNA world hypothesis, self-replicating RNA molecules preceded significant use of proteins. Under the nucleopeptide world hypothesis, significant use of peptides preceded the genetic code and was concurrent with early life's sophisticated use of RNA. Transfer RNA molecules appear to have evolved before modern aminoacyl-tRNA synthetases. It is possible that synthetases replaced an earlier system of ribozymes (RNA enzymes), or that amino acids were recognized by unique pockets in the tertiary structure of proto-tRNAs. It is not known why the genetic code only uses L-amino acids and not D-amino acids. Any evolutionary model for the code's origin must account for its robustness of encoded proteins to errors during DNA replication and during translation. Many single nucleotide errors are synonymous, and those that are not tend to cause the substitution of a biochemically similar amino acid. Even holding the structure of the code the same such that clusters of codons encode the same amino acid, which amino acids are encoded by which sets of codons is "one in a million" with respect to robustness. Biochemically similar amino acids tend to share the same middle nucleotide, while synonymous changes generally happen at the third nucleotide. Amino acids that share the same biosynthetic pathway tend to have the same first base in their codons. This could be an evolutionary relic of an early, simpler genetic code with fewer amino acids that later evolved to code a larger set of amino acids.
In the war's aftermath, the Iraqi government suppressed a series of uprisings until 5 April 1991. Coalition countries responded by establishing two no-fly zones over Iraq's north and south. The United Nations Special Commission sought to end Iraq's weapons of mass destruction programs. In 2003, another US-led coalition invaded and occupied Iraq, beginning the Iraq War. The conflict's environmental impact included Iraqi forces causing over six hundred oil well fires and the largest oil spill in history until that point. US bombing and demolition of Iraqi chemical weapons facilities were concluded to be the primary cause of Gulf War syndrome, experienced by over 40% of US veterans.
The signs and symptoms of ankylosing spondylitis often appear gradually, with peak onset between 20 and 30 years of age. Initial symptoms are usually a chronic dull pain in the lower back or gluteal region combined with stiffness of the lower back. Individuals often experience pain and stiffness that awakens them in the early morning hours. As the disease progresses, loss of spinal mobility and chest expansion, with a limitation of anterior flexion, lateral flexion, and extension of the lumbar spine are seen. Systemic features are common with weight loss, fever, or fatigue often present. Pain is often severe at rest but may improve with physical activity. Inflammation and pain may recur to varying degrees regardless of rest and movement. AS can occur in any part of the spine or the entire spine, often with pain localized to either buttock or the back of the thigh from the sacroiliac joint. Arthritis in the hips and shoulders may also occur. When the condition presents before the age of 18, AS is more likely to cause pain and swelling of large lower limb joints, such as the knees. In prepubescent cases, pain and swelling may also manifest in the ankles and feet, where heel pain and enthesopathy commonly develop. Less common occurrences include ectasia of the sacral nerve root sheaths. About 30% of people with AS will also experience anterior uveitis, causing eye pain, redness, and blurred vision. This is thought to be due to the association that both AS and uveitis have with the presence of the HLA-B27 antigen.
== Detection of phase transitions == The basic principle underlying this technique is that when the sample undergoes a physical transformation such as phase transitions, more or less heat will need to flow to it than the reference to maintain both at the same temperature. Whether less or more heat must flow to the sample depends on whether the process is exothermic or endothermic. For example, as a solid sample melts to a liquid, it will require more heat flowing to the sample to increase its temperature at the same rate as the reference. This is due to the absorption of heat by the sample as it undergoes the endothermic phase transition from solid to liquid. Likewise, as the sample undergoes exothermic processes (such as crystallization) less heat is required to raise the sample temperature. By observing the difference in heat flow between the sample and reference, differential scanning calorimeters are able to measure the amount of heat absorbed or released during such transitions. DSC may also be used to observe more subtle physical changes, such as glass transitions. It is widely used in industrial settings as a quality control instrument due to its applicability in evaluating sample purity and for studying polymer curing.
Sources: en.wikipedia.org
Most listings describe it as a short acetylated peptide with the sequence Ac-LKKTETQ, presented as a region of thymosin beta-4. The label is a trade-style name rather than a standardized chemical name, so the exact content of a given vial depends on the supplier.
No. Thymosin beta-4 is a protein of 43 amino acids, while TB-500 is described as a short fragment of it. The two differ in size, structure, and the range of interactions each can support.
Naming for research peptides is not centrally coordinated, so vendors set their own labels and specifications. Differences in stated sequence, molecular weight, or purity documentation usually trace back to those independent labeling choices.
No. TB-500 is a short synthetic peptide matching residues 17 to 23 of thymosin beta-4, while the parent protein contains 43 residues. The fragment lacks the rest of the protein sequence, so the two are related but not identical.