TB-500 is a synthetic seven-residue peptide, Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln, corresponding to the actin-binding domain of thymosin beta-4 — residues 17 to 23 of the 43-residue parent protein. The single most important fact about it is the one most commonly obscured: TB-500 is not thymosin beta-4. It is a short fragment of it, and the two are routinely conflated in both marketing copy and secondary literature summaries. We supply research-grade TB-500 as lyophilized powder in sealed vials, for laboratory use only.
What is TB-500, precisely
Thymosin beta-4 is a 43-residue intracellular protein and one of the most abundant peptides in mammalian cells. Its principal established function is sequestering monomeric G-actin, holding a reservoir that the cell can release into filament assembly when the cytoskeleton needs to remodel — which is what happens during cell migration, and therefore during tissue repair. The region responsible for actin binding is a short central motif centred on the sequence LKKTETQ.
TB-500 is that motif synthesised alone, with an acetylated N-terminus. Because the whole parent protein has functions beyond actin binding — reported roles in inflammation, angiogenesis and cell survival that do not all map to this heptapeptide — data generated with full-length thymosin beta-4 cannot be assumed to describe TB-500. This is a genuine and consequential distinction, covered further in our article on the fragment versus the whole protein.
Origin and structure
- Sequence. Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln — seven residues, acetylated at the N-terminus, linear, no disulfide bridges.
- Acetylation. The N-terminal acetyl group removes the free amine and its positive charge, which blocks aminopeptidase attack and mimics the context the motif has inside the parent protein.
- Identifiers. CAS 885340-08-9, formula C38H68N10O14, molecular weight 889.02 Da — one of the smallest peptides in our catalog.
- Composition. Two lysines give it a net positive charge at neutral pH and excellent water solubility. No cysteines, methionines or aromatic residues, so no disulfide handling, no oxidation liability, and negligible absorbance at 280 nm.
How TB-500 is thought to work
The mechanism attributed to the LKKTETQ motif is actin sequestration. By binding monomeric G-actin, the motif influences the equilibrium between free monomer and polymerised F-actin filaments, and cytoskeletal remodelling of that kind underlies cell migration — the process by which fibroblasts, endothelial cells and keratinocytes move into a site of tissue damage. Reported downstream observations in the literature include increased endothelial cell migration in angiogenesis assays and accelerated closure in wound-repair models.
Two honest caveats belong here. First, a seven-residue peptide is a weak binder by nature; affinity for actin is modest, and the effect depends on concentration in a way that a high-affinity ligand would not. Second, thymosin beta-4 works intracellularly, and how an externally applied heptapeptide accesses the intracellular actin pool is not fully resolved in the published work. Some papers propose alternative or additional extracellular mechanisms. A laboratory using TB-500 should treat the actin-sequestration account as the leading hypothesis rather than as demonstrated pharmacology in the setting they are studying.
There is a naming problem worth naming. Suppliers frequently list the heptapeptide under the label thymosin beta-4, and reviews sometimes cite full-length protein studies to support statements about the fragment. Because the two differ by more than five-fold in mass and by most of their sequence, this is not a labelling nicety — it determines which literature is relevant to the material in your vial. The reliable check is the certificate: a mass result near 889 Da is the fragment, and a mass near 4,963 Da is the intact protein. Everything else, including product names, is assertion.
What research has examined
- Cell studies. Actin-binding and polymerisation assays, endothelial and fibroblast migration assays, and scratch-closure models.
- Rodent studies. Dermal wound-repair models, cardiac injury models — a substantial strand, since much of the thymosin beta-4 literature originated in cardiac research — and tendon and muscle injury models.
- Full-length thymosin beta-4 trials. Human clinical trials have been conducted with the intact 43-residue protein in dermal and ocular surface indications. These studied a different molecule from TB-500 and should not be cited as evidence for the fragment.
- Human data for TB-500 itself. None of substance. There is no published human trial programme for the heptapeptide.
The cardiac origin of much of this literature also shapes how it should be read. Thymosin beta-4 attracted attention through work on cardiac repair and epicardial cell activation, and several of the most cited mechanistic findings come from that setting rather than from tendon, muscle or dermal models. Effects observed in cardiac tissue involve cell populations and signalling contexts that do not necessarily generalise, so a claim sourced from cardiac work should be labelled as such rather than presented as a general property of the peptide.
Forms and sizes we supply
| Attribute | Specification |
|---|---|
| Form | Lyophilized powder, sealed glass vial |
| Sizes | 5 mg, 10 mg, 20 mg |
| Purity | Greater than or equal to 99% by HPLC, lot-matched COA |
| CAS | 885340-08-9 |
| Molecular weight | 889.02 Da |
| Formula | C38H68N10O14 |
| Sequence | Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln |
| Intended use | Laboratory research only |
Note what the low molecular weight means for molar quantity: 5 mg of TB-500 is about 5.6 micromoles, whereas 5 mg of a 4 kDa peptide is about 1.2 micromoles. Milligram-for-milligram comparisons between peptides of different sizes are meaningless, which is why molar thinking matters — see molecular weight and moles. TB-500 also appears in blends including the Wolverine blend and a topical cream, all within the tissue repair peptides collection.
Reconstitution and storage in a lab context
A worked calculation: a 5 mg vial reconstituted with 2 mL of bacteriostatic water gives 2.5 mg/mL, equal to 2,500 mcg/mL, so 0.1 mL of that solution contains 250 mcg of peptide — which for this molecule is roughly 281 nanomoles. TB-500 is among the easiest peptides to prepare: small, highly water-soluble, no disulfide bridge, no oxidation-prone residues, and no aggregation tendency.
Store sealed lyophilized powder at minus 20 degrees Celsius, protected from light and moisture; hold reconstituted solution at 2 to 8 degrees Celsius and use within the study window. Aliquot at reconstitution rather than repeatedly freezing and thawing. One caution specific to very small peptides: adsorption to glass and plastic surfaces is proportionally significant at low concentrations, so low-binding plasticware and carrier protein in assay buffers are standard mitigations. See our reconstitution guide.
Purity, COA and how to read it
Expect an HPLC chromatogram with main-peak area percentage, mass spectrometry identity against the theoretical 889.02 Da, net peptide content, lot number and analysis date. Three checks are specific to this peptide. Acetylation state: a non-acetylated heptapeptide differs by 42 daltons, easily resolved by mass spectrometry and worth confirming, since the acetyl group is a functional part of the molecule and not a synthesis artefact. Detection wavelength: with no aromatic residues, quantification is at around 214 nm, so a 280 nm-only chromatogram is a red flag. And identity versus the full-length protein: a supplier describing a product as thymosin beta-4 while shipping the heptapeptide is describing an 889 Da peptide as a 4,963 Da protein, a discrepancy any mass result exposes immediately. See how to read a COA.
A last practical note on interpreting results with a peptide this small. At 889 Da, TB-500 sits near the boundary where mass spectrometry, chromatography and even filtration behave differently from the way they do with larger peptides: it passes through molecular weight cut-off membranes that retain most research peptides, it elutes early on reversed-phase gradients, and it is easily lost during sample preparation steps designed for proteins. Any workflow adapted from work on larger peptides should be validated for recovery before its results are trusted, because unrecognised loss during processing produces exactly the pattern of weak, inconsistent effects that this peptide is often reported to show.
Regulatory status
TB-500 is not an approved medicine in any jurisdiction. It appears on the World Anti-Doping Agency prohibited list, and in the United States thymosin beta-4 related substances have been placed in the FDA category of bulk substances not eligible for compounding. Research-grade TB-500 is supplied as a laboratory reference chemical, research use only, not approved or formulated for administration to humans or animals. See research use only, explained.
Related peptides and comparisons
The standard comparison is BPC-157 vs TB-500, and the two are supplied together as the Wolverine blend. For the intact protein see full-length thymosin beta-4; related repair tools include BPC-157.