If you have been reading about thymosin beta-4 fragment 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 2026-06-11. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
The compound circulates in the literature as a research reagent rather than an approved therapeutic. Regulatory agencies in several countries have not authorized it for medical use, and sporting bodies list related thymosin beta-4 peptides among prohibited substances. Suppliers typically market it with a purity figure and a certificate of analysis, while peer-reviewed clinical reports remain sparse. Discussions therefore often separate laboratory findings from anecdotal reports, and reviewers tend to note the small size and methodological limits of the available studies.
TB-500 refers to a synthetic peptide fragment derived from the actin-binding region of thymosin beta-4, a protein present in most mammalian cells. The full protein contains forty-three amino acids, while the commonly sold fragment is a much shorter acetylated sequence, often cited as LKKTETQ. The fragment retains part of the actin-binding motif but lacks the remainder of the parent protein. Material sold under this name is usually lyophilized powder intended for laboratory research, and it is not a finished pharmaceutical product.
| Property | Value | Notes |
|---|---|---|
| Molecular formula | C38H68N10O14 | Acetylated heptapeptide form |
| Monoisotopic mass | 888.5 Da | Average mass about 889 Da |
| Appearance | White to off-white solid | Usually supplied as lyophilised powder |
| Solubility class | Highly water soluble | Also dissolves in aqueous buffers |
| Common synonyms | Tbeta4 fragment, thymosin beta-4 (17-23) | Refer to the same 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.
Discussion of TB-500 appears in several distinct literatures that rarely cite one another. Peer-reviewed studies usually describe in vitro assays or small animal experiments and are cautious about extrapolation. Veterinary and sports communities circulate anecdotal reports with limited methodological detail. Commercial listings add a third layer, often using the name interchangeably with thymosin beta-4 even though the two molecules differ in size and sequence. Regulatory status varies by country, and the compound is not a licensed medicine in most jurisdictions, so readers comparing sources should check which molecule and which purity each source actually describes.
TB-500 is a synthetic seven-residue peptide whose sequence, LKKTETQ, matches the N-terminal actin-binding region of thymosin beta-4. It is usually supplied in an N-terminally acetylated form, a modification that blocks the free amino terminus and can influence behavior in solution. In the research literature the same sequence appears under several names, including thymosin beta-4 fragment and shortened thymosin beta-4. Because it is a short peptide rather than the full 43-residue parent protein, its measured properties differ from those reported for thymosin beta-4 as a whole, and the two are not interchangeable in experimental design.
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.
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.
=== Identification of Peptide Substrates === This can be applied to find the best substrates for proteolytic enzymes. The substrate is displayed on the bacterial cell surface between an affinity ligand and the scaffold, and the kinetics of substrate proteolysis is measured using FACS.
=== Occurrence in bacteria === Hydrogen cyanide is produced by various soil bacteria, including cyanobacteria and representatives of the genera Aeromonas, Bacillus, and Pseudomonas. Biosynthesis proceeds from glycine. A group of alkanenitriles was isolated from Pseudomonas veronii: dodecannitrile, tridecannitrile, tetradecanenitrile, pentadecannitrile, and hexadecannitrile, as well as compounds of similar chain length containing a double bond. From Micromonospora echinospora, structurally related compounds were also isolated, differing by a terminal methyl branch, a double bond, or both. A cyanohydrin containing a phosphonic acid moiety is known from Streptomyces regensis. The aetokthonotoxin from the cyanobacteria Aetokthonos hydrillicola is a brominated indole derivative bearing a nitrile group. It is a potent neurotoxin that frequently causes mortality in bald eagles that ingest it.
== Factors affecting topical drug absorption == Topical drug absorption depends on two major factors – biological and physicochemical properties. The first factor concerns body structure effects on the drugs. The degradation of drugs can be affected by the site of applications. Some studies discovered different percutaneous absorption patterns. Apart from the place, age also affects the absorption as the skin structure changes with age. The lowered collagen and broadened blood capillary networks happen with aging. These features alter the effectiveness of absorption of both hydrophilic and lipophilic substances into stratum corneum underneath the surface of the skin. The skin surface integrity can also affect the permeability of drugs such as the density of hair follicles, sweat glands or disintegrated by inflammation or dehydration. The other factor concerns metabolism of medications on skin. When the percutaneous drug is applied on skin, it will be gradually absorbed down the skin. Normally, when the drugs are absorbed, they will be metabolised by various enzymes in our body and the amount will be lower. The exact amount delivered to the target action site determines the potency and bioavailability of the drugs. If the concentration is too low, the therapeutic effect is impeded; if the concentration is too high, drug toxicity may happen to cause side effects or even do harm to our body. For the topical drug delivery way, degradation of drugs in skin is very low compared to liver.
== Professional activities == After earning a Ph.D. degree in biochemistry, a medical degree, and completing a research postdoctoral fellowship at the University of Wisconsin–Madison, Holick completed a residency in medicine at the Massachusetts General Hospital in Boston. He has been practicing adult and pediatric endocrinology since 1978 and is professor of medicine, physiology and biophysics and director of the Bone Health Care Clinic and the Heliotherapy, Light, and Skin Research Center at Boston University Medical Center. It provides extensive evaluation and treatment programs for children and adults with various metabolic bone diseases including osteoporosis, osteomalacia, stress fractures in young athletic women and men, and minimum trauma and nontraumatic fractures in infants, children and adults with hypermobility syndromes, osteogenesis imperfecta, and Ehlers–Danlos syndrome. He has been director of the General Clinical Research Unit at Boston University for several years. Holick serves as chair of NASA's "Human Health Countermeasures Element" Standing Review Panel, chair of the Endocrine Practice Guidelines Committee for Vitamin D, and editor-in-chief of the medical journal Clinical Laboratory.
== Applications == Applications include alteration of gene expression - both as inhibitor and promoter in different cases, antigene and antisense therapeutic agent, anticancer agent, antiviral, antibacterial and antiparasitic agent, molecular tools and probes of biosensor, detection of DNA sequences, and nanotechnology. PNAs can be used to improve high-throughput 16S ribosomal RNA gene sequencing of plant and soil samples by blocking amplification of contaminant plastid and mitochondrial sequences. Cellular – Functional Antagonism/Inhibition. In 2001, Strauss and colleagues reported the design of an application for PNA oligomers in living mammalian cells. The Xist chromatin binding region was first elucidated in female mouse fibroblastic cells, and embryonic stem cells though the use of a PNA molecular antagonist. The novel PNA approach directly demonstrated function of a lncRNA. The long non-coding (lncRNA) RNA, Xist directly binds to the inactive X-chromosome. Functional PNA inhibition experiments revealed that specific repeat regions of the Xist RNA were responsible for chromatin binding, and hence could be considered domain regions of the RNA transcript. The PNA molecular antagonist was administered to living cells and functionally inhibited the association of Xist with inactive X-chromosome using the approach for studying noncoding RNA function in living cells called peptide nucleic acid (PNA) interference mapping. In the reported experiments, a single 19-bp antisense cell-permeating PNA targeted against a particular region of Xist RNA caused the disruption of the Xi.
Sources: en.wikipedia.org
Ethanol-containing beverages can cause alcohol flush reactions, exacerbations of rhinitis, and, more seriously and commonly, bronchoconstriction in patients with a history of asthma, and in some cases, urticarial skin eruptions, and systemic dermatitis. Such reactions can occur within 1–60 minutes of ethanol ingestion, and may be caused by:
Peukert ended his essay stating that there were debates about "our dealings with others, notably those different from ourselves. Recent debates about foreign migrants and AIDs present a conflicting picture. On one hand, we can see the continuing survival of a discourse on segregation, untouched by any historical self-consciousness. On the other hand, however, there is a considerable body of opinion pledging for tolerance and responsibility that spring from an awareness of German history and of the genesis of the "Final Solution" from the spirit of science".
Criminal law is based on the Indian Penal Code originally intended for British India, and was at the time as a crown colony also adopted by the British colonial authorities in Singapore and remains the basis of the criminal code in the country with a few exceptions, amendments and repeals since it came into force. Trial by jury was abolished in 1970. Singapore is known for its strict laws and conservative stances on crime; both corporal punishment (by caning) and capital punishment (by hanging) are retained and commonly used as legal penalties.
== Model estimation == NONMEM estimates its models according to principles of maximum likelihood estimation. nonlinear mixed-effects model generally do not have close-formed solutions, and therefore specific estimation methods are applied, such as linearization methods as first-order (FO), first-order conditional (FOCE) or the laplacian (LAPL), approximation methods such as iterative-two stage (ITS), importance sampling (IMP), stochastic approximation estimation (SAEM) or direct sampling.
Sources: en.wikipedia.org
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.
It consists of leucine, lysine, lysine, threonine, glutamic acid, threonine, and glutamine in that order. The N-terminal leucine is usually acetylated in the forms described in catalogues.
Controlled human data is limited, and most published findings come from cell culture or animal work. This makes it difficult to state clinical effects with confidence.
TB-500 is a name used for a short synthetic peptide fragment taken from the actin-binding region of thymosin beta-4. Material sold under this label is usually a lyophilized powder supplied for laboratory research rather than a licensed medicine. The commonly cited sequence is LKKTETQ.