If you have been reading about actin binding 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.
Last reviewed on 2026-02-18. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
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.
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.
Published research on the intact protein is substantial, covering actin regulation, cell migration, and wound models. Research using the heptapeptide fragment specifically is far smaller, and much of the circulating material originates in supplier documentation rather than peer-reviewed reports. Where fragment studies do exist, they often employ different sequences, chain lengths, or terminal modifications, which complicates direct comparison across papers. Readers encountering claims about TB-500 should therefore separate evidence about thymosin beta-4 from evidence about the fragment itself.
Discussion of the compound frequently appears alongside other short peptides described as fragments of larger proteins. That grouping is convenient but can be misleading, because fragment length, charge, and modification state determine how a peptide behaves in solution and in any experimental system. A seven-residue acetylated peptide and a full-length protein differ in mass by roughly an order of magnitude, and they cannot be assumed to share distribution or binding properties. Precision about which molecule is under discussion is the single most useful step when reading such material.
| 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 |
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.
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.
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.
Reconstitution of a lyophilized peptide is normally done with sterile water or a suitable buffer under aseptic conditions. Adding solvent down the vial wall and allowing gentle dissolution instead of vigorous vortexing reduces the chance of aggregation, which can lower the effective concentration of the resulting solution. Concentrated stocks are usually diluted into working buffer shortly before use. Because no standard preparation protocol exists for TB-500 specifically, laboratories adapt general peptide handling practice, and reported results may reflect differing preparation choices.
Dry peptide powder is commonly kept at −20 °C in a desiccated container away from light, a practice that limits moisture uptake and oxidation. Once dissolved, solutions are generally held at 2–8 °C for short periods or frozen at −20 °C or lower for longer storage, with repeated freeze-thaw cycles avoided. Hydrolysis and oxidation are the main degradation routes for peptides in solution, and both accelerate at higher temperature or extreme pH. Published stability data specific to TB-500 are limited, so shelf life should be treated as uncertain.
These performances can be found on their social media accounts, such as YouTube and Facebook. In addition, they collaborated with Dave Mason for a cover of Traffic's "Feelin' Alright" and Peter Frampton for a cover of Eric Clapton's "Let it Rain". On August 6, 2021, the Doobie Brothers released the EP of four songs that would eventually be featured on their fifteenth studio album. These songs included Johnston's "Don't Ya Mess with Me" and "Oh Mexico" along with Simmons's "Better Days" and "Cannonball". After just over 18 months of not being able to tour due to the COVID-19 pandemic, the band (with McDonald back in the fold) finally began their 50th Anniversary Tour at the Iowa State Fair on Sunday, August 22, 2021. The first leg of the tour concluded at the PPL Center in Allentown, Pennsylvania on October 29, 2021, and the second leg began in West Palm Beach, Florida on June 2, 2022. Bill Payne left the touring band at the end of the first leg, citing his desire to commit "100%" to Little Feat. He was not replaced, and the tour continued with McDonald returning to his original role of primary keyboardist. The Doobie Brothers were featured musical guests on Jimmy Kimmel Live! on Thursday, September 23, 2021. On October 29, 2021, the band released Liberté, their fifteenth full-length studio album and first album of original material in 11 years. All of the tracks on the album were co-written with John Shanks. Shanks is known for his work with Bon Jovi, Sheryl Crow, and Melissa Etheridge, to name a few. Original drummer John Hartman died on December 29, 2021.
Elemental sulfur is one of the oldest fungicides and pesticides. "Dusting sulfur", elemental sulfur in powdered form, is a common fungicide for grapes, strawberry, many vegetables and several other crops. It has a good efficacy against a wide range of powdery mildew diseases as well as black spot. In organic production, sulfur is the most important fungicide. It is the only fungicide used in organically farmed apple production against the main disease apple scab under colder conditions. Biosulfur (biologically produced elemental sulfur with hydrophilic characteristics) can also be used for these applications. Standard-formulation dusting sulfur is applied to crops with a sulfur duster or from a dusting plane. Wettable sulfur is the commercial name for dusting sulfur formulated with additional ingredients to make it water miscible. It has similar applications and is used as a fungicide against mildew and other mold-related problems with plants and soil. Elemental sulfur powder is used as an "organic" (i.e., "green") insecticide (actually an acaricide) against ticks and mites. A common method of application is dusting the clothing or limbs with sulfur powder. A diluted solution of lime sulfur (made by combining calcium hydroxide with elemental sulfur in water) is used as a dip for pets to destroy ringworm (fungus), mange, and other dermatoses and parasites. Sulfur candles of almost pure sulfur were burned to fumigate structures and wine barrels, but are now considered too toxic for residences.
Mohammed said al-Qaeda initially planned to target nuclear installations rather than the World Trade Center and the Pentagon, but decided against it, fearing things could "get out of control." Final decisions on targets, according to Mohammed, were left in the hands of the pilots. If any pilot could not reach his intended target, he was to crash the plane.
The 8.5 kg Mini- 11 and 25 kg Mini-12 can produce resolution mass spectra up to m/z 600, a range that makes it useful for studying metabolites, lipids, and other small molecules. The group also developed and incorporated a digital microfluidic platform to the MMS with the application to extract and quantify drugs in urine. Mini 12 can perform MS5 and analyze directly such complex samples as whole blood, untreated food, and environmental samples, without sample preparation or chromatographic separation.
== Related compounds == Numerous other compounds similar to levonantradol were also developed at the same time, including CP 42,096, CP 47,497, CP 55,940 and CP 55,244. The desacetyl derivative of levonantradol (DALN or CP 54,939) and its N-methyl derivative, as well as the tetracyclic analogue all have similar activity to levonantradol itself.
Sources: en.wikipedia.org
== Biological role == Cadmium has no known function in most organisms, and is toxic. Cadmium is considered an environmental pollutant hazardous to living organisms. A cadmium-dependent carbonic anhydrase has been found in some marine diatoms, which live in environments with low zinc concentrations. Exposure to cadmium leads to raised levels in the blood cells for a number of months. In vertebrates cadmium is preferentially absorbed in the kidneys but also in the liver and bones. Up to about 30 mg of cadmium is commonly inhaled throughout human childhood and adolescence. Cadmium is eliminated from the body in very small amounts and mainly through urine resulting in a biological half-life of 20 to 40 years. Cadmium is under research for its potential toxicity to increase the risk of cancer, cardiovascular disease, and osteoporosis.
Transitional epithelium, also known as urothelium is a type of stratified epithelium that changes shape in response to stretching.. Transitional epithelium usually appears cuboidal when relaxed and squamous when stretched. This tissue consists of multiple layers of epithelial cells which can contract and expand in order to adapt to the degree of distension needed. Transitional epithelium lines all of the organs of the urinary system – the kidneys, ureters, bladder, and the urethra, hence its alternative name of urothelium. The bladder, for example, has a need for great distension.
== Role == Acetyl-CoA is a metabolic intermediate that is involved in many metabolic pathways in an organism. It is produced during the breakdown of glucose, fatty acids, and amino acids, and is used in the synthesis of many other biomolecules, including cholesterol, fatty acids, and ketone bodies. Acetyl-CoA is also a key molecule in the citric acid cycle, which is a series of chemical reactions that occur in the mitochondria of cells and is responsible for generating energy in the form of ATP. In addition, acetyl-CoA is a precursor for the biosynthesis of various acetyl-chemicals, acting as an intermediate to transfer an acetyl group during the biosynthesis of those acetyl-chemicals. Acetyl-CoA is also involved in the regulation of various cellular mechanisms by providing acetyl groups to target amino acid residues for post-translational acetylation reactions of proteins.
=== Epigenetic studies === As more research is conducted on determinants of longevity, the impact of genetics and lifestyle are becoming an important question. Scientists have been looking for the genetic and molecular processes that affect aging. Recent research shows that a relationship exists between aging and genes that work on keeping cells healthy and support their most basic functions, cell metabolism and maintenance. By measuring the biological age of various tissues from centenarians, researchers may be able to identify tissues that are protected from aging effects. According to a study of 30 different body parts from centenarians and younger controls, the cerebellum is the youngest brain region (and probably body part) in centenarians (about 15 years younger than expected) according to an epigenetic biomarker of tissue age known as epigenetic clock. These findings could explain why the cerebellum exhibits fewer neuropathological hallmarks of age related dementias compared to other brain regions. Further, the offspring of semi-supercentenarians (subjects who reached an age of 105–109 years) have a lower epigenetic age than age-matched controls (age difference=5.1 years in peripheral blood mononuclear cells) and centenarians are younger (8.6 years) than expected based on their chronological age.
=== Fibrous === The fibrous pericardium is the outside layer of the pericardium, made up of dense and loose connective tissue. While capable of some change in shape, it is largely non-pliable, which acts to protect the heart against blunt forces and sudden pressure change from the outside. It is continuous with the outer adventitial layer of the neighboring great blood vessels, fused with the central fibrous area of the diaphragm on its posterior aspect and attached to the posterior surface of the sternum by the sternopericardial ligaments.
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.
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.