TB-500 is the name given in the research-chemical market to material derived from thymosin β4 — and the TB-500 research peptide most commonly supplied is the N-terminally acetylated 17–23 fragment, Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln, which carries the actin-binding motif of the parent 43-amino-acid protein. This guide separates the two molecules, sets out the published actin-sequestration mechanism, summarises the preclinical literature, and covers identity checks, solution preparation and storage for laboratory work.
Key takeaways
- Thymosin β4 (Tβ4) is a naturally occurring 43-residue peptide, CAS 77591-33-4, formula C212H350N56O78S, MW ≈ 4963.5 Da. It is the principal intracellular G-actin sequestering peptide.
- TB-500 is a market name, not a chemical name. Analytical work published in 2012 identified the acetylated 17–23 fragment (Ac-LKKTETQ, MW ≈ 889 Da) in a product sold under that label.
- The LKKTETQ motif at residues 17–23 is the region of Tβ4 associated with actin binding, which is why the fragment is the part that was isolated and synthesised.
- The described mechanism is actin sequestration: Tβ4 binds monomeric G-actin, maintaining a mobilisable pool that supports cytoskeletal remodelling and cell migration.
- Published rodent and cell work reports effects on keratinocyte migration, re-epithelialisation, angiogenesis and cardiac cell migration; the full-length protein has far more supporting data than the fragment.
- Because the two molecules differ by roughly 4,000 Da, mass spectrometry on the certificate of analysis is the only reliable way to know which one is in a vial.
- Thymosin β4 and TB-500 are listed by WADA under S0. GenoPept supplies TB-500 as lyophilised vials for laboratory research only.
What is TB-500?
TB-500 is a trade designation rather than a chemical identity. It entered circulation as a research and veterinary product marketed in reference to thymosin β4, and analytical chemists working on doping control examined what the material actually contained. A 2012 paper in Drug Testing and Analysis synthesised and characterised the N-terminally acetylated 17–23 fragment of thymosin β4 after identifying it in a product sold as TB-500.
That matters because the two candidate molecules are very different in size. Full-length Tβ4 is a 43-residue peptide of roughly 4963 Da. The acetylated heptapeptide Ac-LKKTETQ is roughly 889 Da — about one fifth the mass, one sixth the chain length, and a very different synthesis and purification proposition.
Both are legitimate research materials. What is not legitimate is treating the labels as interchangeable without checking. GenoPept lists its product explicitly as TB-500 (Thymosin Beta-4 Fragment), and the batch certificate of analysis reports the measured mass.
The naming confusion has a practical cost in the literature too. Search results, supplier pages and secondary summaries routinely attach full-length thymosin β4 findings to the TB-500 name, so a researcher reading around the compound can accumulate a reference list in which almost nothing was performed with the material they hold. Reading the methods section for the actual peptide used is the only reliable filter.
Thymosin β4 vs the TB-500 fragment
Thymosin β4 is a small, intrinsically disordered, highly acidic peptide found in most mammalian cell types and in high concentration in platelets. Its 43-residue sequence is SDKPDMAEIEKFDKSKLKKTETQEKNPLPSKETIEQEKQAGES, and the mature protein is N-terminally acetylated in vivo. The actin-binding region sits at residues 17–23.
| Property | Thymosin β4 (Tβ4) | TB-500 fragment (Ac-LKKTETQ) |
|---|---|---|
| Chain length | 43 residues | 7 residues |
| Sequence | SDKPDMAEIEKFDKSKLKKTETQEKNPLPSKETIEQEKQAGES | Leu-Lys-Lys-Thr-Glu-Thr-Gln (positions 17–23) |
| CAS number | 77591-33-4 | Not assigned a widely used single CAS entry |
| Molecular formula | C212H350N56O78S | Heptapeptide plus N-terminal acetyl group |
| Molecular weight | ≈ 4963.5 Da | ≈ 889 Da |
| N-terminus | Acetylated in the mature natural form | Acetylated |
| Oxidation risk | Methionine at position 6 | No Met, Cys or Trp |
| Analytical signature | Multiply charged envelope on ESI-MS | Single dominant low-mass ion |
TB-500 mechanism: actin sequestration and cell migration
The mechanism described for thymosin β4 is actin sequestration. Tβ4 binds monomeric globular actin (G-actin) in a one-to-one complex, holding it in a form that is not immediately available for filament assembly but can be released when the cell needs to build new filamentous actin (F-actin). Goldstein and colleagues characterised this as an actin-sequestering protein that “moonlights” in tissue repair.
That buffering role links directly to cell motility. Directed migration — a keratinocyte crossing a wound edge, an endothelial cell forming a tube, a cardiac cell relocating after injury — requires rapid, polarised remodelling of the actin cytoskeleton. A regulated reserve of sequestered monomer is part of how a cell achieves that.
The LKKTETQ motif is the part of the sequence associated with actin binding, which is the rationale for isolating it as a standalone fragment. Whether a free heptapeptide reproduces the behaviour of the same motif embedded in a 43-residue disordered chain is a genuinely open question in the literature, and one of the reasons full-length Tβ4 and TB-500 should not be treated as pharmacologically equivalent.
What the published research reports
The thymosin β4 literature is older and more independently distributed than the BPC-157 literature, with contributions from the Goldstein and Kleinman groups at George Washington University and the NIH, cardiovascular groups, and ophthalmology researchers. Almost all of it concerns the full-length peptide.
| Study focus | Model | Reported observation | Reference |
|---|---|---|---|
| Cutaneous wound repair | Rat full-thickness wounds; Boyden chamber assay | Increased re-epithelialisation and wound contraction; roughly two- to three-fold stimulation of keratinocyte migration in vitro | Malinda 1999 |
| Actin biology | Review of biochemical and cell studies | Tβ4 framed as the principal G-actin sequestering peptide with an additional extracellular repair role | Goldstein 2005 |
| Cardiac injury | Mouse myocardial infarction; cardiac cell culture | Integrin-linked kinase activation; increased cardiac cell migration and survival reported | Bock-Marquette 2004 |
| Multi-tissue animal work | Review of rodent and rabbit models | Tβ4 described as a multifunctional tissue repair and regeneration peptide across several organ systems | Philp 2010 |
| Product identity | Analytical chemistry / doping control | The N-terminally acetylated 17–23 fragment was synthesised and characterised after being identified in a product sold as TB-500 | Esposito 2012 |
Thymosin β4 has also attracted more formal development interest than most compounds in this category, including reported prospective randomised work on chronic venous ulcers and sustained cardiovascular research following the 2004 Nature paper. No approved product has emerged from any of it, and none of that work used the isolated heptapeptide — a point worth holding onto when a summary page cites “clinical evidence for TB-500”.
Two practical conclusions follow. First, when a supplier or a summary article cites “TB-500 research”, the underlying paper is usually a full-length Tβ4 study — worth knowing before designing an experiment around the fragment. Second, the fragment’s own published characterisation is largely analytical rather than pharmacological, which is a gap rather than a fault.
Identity: knowing which molecule is in the vial
The single most useful check on a TB-500 batch is the mass-spectrometry trace. A ≈889 Da signal indicates the acetylated heptapeptide; a multiply charged envelope deconvoluting to ≈4963 Da indicates full-length Tβ4. The gap is so large that no ambiguity should survive a competent MS run.
Reconstitution, concentration reference and storage
TB-500 dissolves readily in aqueous diluent. The table below gives concentration references for preparing laboratory stock solutions from a lyophilised vial — these are solution-chemistry figures only.
- Equilibrate the vial. Bring it to room temperature before piercing the stopper so moisture does not condense onto the cake.
- Choose the target concentration. Work back from the assay volume you need, using Table 3 or the reconstitution calculator.
- Add diluent down the vial wall. A slow stream against the glass avoids foaming, which shears peptide and creates aggregates.
- Swirl, do not shake. Let the material go into solution unaided; vigorous agitation is unnecessary for a peptide of this size.
- Check clarity. The solution should be visually clear. Persistent haze warrants an HPLC check before use.
- Aliquot and record. Split into single-use working volumes, and log batch, diluent, volume, concentration and date.
| Peptide in vial | Diluent volume | Concentration | Amount per 0.1 mL | Approx. molarity (fragment, MW 889) |
|---|---|---|---|---|
| 2 mg | 1 mL | 2.00 mg/mL | 200 mcg | ≈ 2.25 mM |
| 5 mg | 1 mL | 5.00 mg/mL | 500 mcg | ≈ 5.62 mM |
| 5 mg | 2 mL | 2.50 mg/mL | 250 mcg | ≈ 2.81 mM |
| 5 mg | 3 mL | 1.67 mg/mL | 167 mcg | ≈ 1.87 mM |
| 10 mg | 2 mL | 5.00 mg/mL | 500 mcg | ≈ 5.62 mM |
| 10 mg | 3 mL | 3.33 mg/mL | 333 mcg | ≈ 3.75 mM |
Purity, COA and batch checks
A useful TB-500 certificate reports reversed-phase HPLC purity as a percentage of total peak area at a stated wavelength, alongside a mass-spectrometry trace confirming identity. For the heptapeptide, expect a simple chromatogram with one dominant peak; for full-length Tβ4, a broader peak shape is normal given the peptide’s disordered, acidic character.
Three checks are worth making every time: the batch number on the certificate matches the vial, the reported mass matches the molecule you ordered, and the chromatogram itself is reproduced rather than summarised. GenoPept publishes per-batch third-party COAs at /coa-certificates/, and the COA reading guide annotates each field.
TB-500 in the GenoPept store
Frequently asked questions
Is TB-500 the same as thymosin beta-4?
Not necessarily. Thymosin β4 is a defined 43-residue peptide with CAS number 77591-33-4 and a molecular weight of about 4963 Da. TB-500 is a market label; published analytical work identified the acetylated 17–23 fragment, Ac-LKKTETQ, of about 889 Da in a product sold under that name. The certificate of analysis mass is what settles which one a batch contains.
What is the LKKTETQ motif?
LKKTETQ is the seven-residue stretch at positions 17–23 of thymosin β4 associated with actin binding. It sits within the WH2-type actin-binding region of the peptide. Isolating this motif as a standalone acetylated heptapeptide is the basis of the shorter material sold as TB-500.
What is the molecular weight of TB-500?
The acetylated 17–23 fragment has a molecular weight of approximately 889 Da. Full-length thymosin β4 is approximately 4963.5 Da, with the molecular formula C212H350N56O78S. Because the difference is roughly 4,000 Da, mass spectrometry distinguishes them unambiguously.
Does TB-500 need to be refrigerated?
Lyophilised TB-500 is stored cold and away from light, and reconstituted solutions are refrigerated and used within a short window. The heptapeptide fragment contains no methionine or cysteine, so oxidation is less of a concern than for full-length thymosin β4, which carries a methionine at position 6.
How does TB-500 differ from BPC-157?
They come from different origins and are described through different mechanisms. BPC-157 is a synthetic fragment of a gastric protein, discussed in terms of nitric oxide signalling and VEGFR2 upregulation. TB-500 derives from thymosin β4 and is discussed in terms of actin sequestration and cell migration. Our comparison guide sets the two side by side.
What does actin sequestration mean?
Actin exists in cells as free monomers (G-actin) and as assembled filaments (F-actin). A sequestering peptide binds monomers and holds them in a non-polymerising but releasable state. This buffers the monomer pool so a cell can rapidly build filaments where they are needed, which is central to directed migration and cytoskeletal remodelling.
Is TB-500 banned in sport?
Thymosin β4 and TB-500 fall under the World Anti-Doping Agency’s S0 category, which covers substances not approved for human therapeutic use by any governmental regulatory health authority. Sports-science laboratories handling reference material should treat it accordingly. This is general information, not legal advice.
How is TB-500 purity assessed?
By reversed-phase HPLC, reported as the main peak’s share of total peak area at a stated detection wavelength, with mass spectrometry confirming identity. For the heptapeptide, a clean single dominant peak is expected. Purity percentage and net peptide content are separate figures — counter-ions and residual water contribute mass but not peptide.
References
- Malinda KM, et al. Thymosin beta4 accelerates wound healing. Journal of Investigative Dermatology. 1999;113(3):364–368. PubMed
- Goldstein AL, Hannappel E, Kleinman HK. Thymosin β4: actin-sequestering protein moonlights to repair injured tissues. Trends in Molecular Medicine. 2005. PubMed
- Bock-Marquette I, et al. Thymosin beta4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repair. Nature. 2004;432(7016):466–472. PubMed
- Philp D, Kleinman HK. Animal studies with thymosin β4, a multifunctional tissue repair and regeneration peptide. Annals of the New York Academy of Sciences. 2010;1194:81–86. doi:10.1111/j.1749-6632.2010.05479.x
- Esposito S, Deventer K, et al. Synthesis and characterization of the N-terminal acetylated 17-23 fragment of thymosin beta 4 identified in TB-500, a product suspected to possess doping potential. Drug Testing and Analysis. 2012. doi:10.1002/dta.1402
Research-grade TB-500, batch-verified
GenoPept supplies TB-500 (thymosin beta-4 fragment) as lyophilised vials with a per-batch third-party certificate of analysis covering HPLC purity and mass-spectrometry identity, dispatched from the UK, strictly for laboratory research.