What Is TB-500? How It Differs From Thymosin Beta-4

TB-500 is a synthetic peptide modelled on the actin-binding site of thymosin beta-4 (Tβ4). When an anti-doping laboratory analysed a commercial TB-500 preparation, the key ingredient was the seven-residue sequence LKKTETQ with an acetylated N-terminus, corresponding to amino acids 17–23 of Tβ4 (Ho et al., 2012). TB-500 is therefore a fragment, not the full 43-residue protein, and that distinction shapes how the research literature should be read.

For laboratory research use only. The compounds discussed are not approved for human or veterinary use and are not drugs, foods or cosmetics. This article summarises published research and is not medical advice.

Key points

TB-500 reproduces a short active region (17-23, LKKTETQ) of thymosin beta-4.
Full-length Tβ4 is a 43-amino-acid, ~4.9 kDa protein and the main G-actin-sequestering peptide in vertebrate cells.
Different Tβ4 activities map to different short sequences; LKKTETQ is linked to cell migration and angiogenesis.
Most published biology uses full-length Tβ4, not TB-500.
Label composition varies between suppliers; check the COA for the exact sequence.

TB-500 vs thymosin beta-4

	Thymosin beta-4 (Tβ4)	TB-500 (as characterised by Ho et al.)
Length	43 amino acids	7 amino acids (17-23)
Sequence	Ac-SDKPDMAEIEKFDKSKLKKTETQEKNPLPSKETIEQEKQAGES	Ac-LKKTETQ
Molecular formula / weight	C₂₁₂H₃₅₀N₅₆O₇₈S, ~4963 g/mol	~890 g/mol (acetylated heptapeptide)
Occurrence	Natural; found in almost all cells and body fluids	Synthetic
Structure in solution	Largely unfolded; folds on binding G-actin	Short flexible peptide
Research base	Extensive cell, animal and some clinical work	Limited; analytical and doping-control literature

Our TB-500 (thymosin beta-4 fragment) lots are supplied with HPLC purity and mass-spectrometry identity data, so the sequence in each vial can be confirmed.

What thymosin beta-4 does

Tβ4 was originally isolated from thymus extracts (thymosin fraction 5) and assumed to be a thymic hormone. In 1990 it was found to sequester G-actin; it is now regarded as the main intracellular G-actin-sequestering peptide in most vertebrate cells (Hannappel, 2007). Tβ4 is largely unstructured in solution. One review proposed that this flexibility lets it recognise multiple binding partners, which may explain the range of functions attributed to it (Bubb, 2003).

Active sites within Tβ4

A key paper mapped several Tβ4 activities to short peptide sequences (Sosne et al., 2010):

Region	Sequence	Activity attributed
N-terminal tetrapeptide	Ac-SDKP (1-4)	Generally anti-inflammatory and anti-fibrotic
N-terminal 15-mer	1-15 (includes Ac-SDKP)	Cell survival, anti-apoptotic
Central actin-binding domain	LKKTET (17-22) + Q	Angiogenesis, cell migration, wound-repair processes

This map is the scientific rationale for TB-500: it isolates the actin-binding, migration-associated segment. It also means TB-500 lacks the Ac-SDKP region and the rest of the molecule, so activities linked to those parts should not be expected from it.

Research context

Full-length Tβ4 has been studied in models of eye, skin, heart and brain injury, and a 2015 review described clinical trials of Tβ4 in several of these areas (Goldstein et al., 2015). These studies used Tβ4, not TB-500. For the heptapeptide itself, the peer-reviewed literature is dominated by analytical chemistry. Ho and colleagues developed an LC-MS method that detects N-acetylated LKKTETQ and its metabolites in equine urine and plasma, after first identifying likely metabolites in vitro (Ho et al., 2012). Their paper also notes the claims made for TB-500 in veterinary marketing, which are not the same as demonstrated effects.

Handling in the lab

Lyophilized powder; store at −20 °C, sealed and dark.
The two lysines make the peptide basic and readily water-soluble; reconstitute with bacteriostatic or sterile water (method).
Store solutions at 2–8 °C; avoid repeated freeze–thaw.
Verify identity by MS: the expected mass differs greatly between the heptapeptide and full-length Tβ4.
Calculate concentrations with the peptide reconstitution calculator.

Open questions

How much of full-length thymosin beta-4’s activity does the isolated 17-23 fragment reproduce in the same assays? Direct side-by-side comparisons are scarce.
What is the plasma half-life of N-acetylated LKKTETQ? Metabolites have been identified, but formal pharmacokinetics have not been published.
Do all commercial TB-500 products contain the same sequence? Some may contain longer fragments or full-length Tβ4, which is why identity testing by MS matters.

Related research

Frequently asked questions

What is TB-500?

TB-500 is a synthetic peptide based on the actin-binding region of thymosin beta-4. An analytical study of a commercial TB-500 preparation identified its key ingredient as the heptapeptide LKKTETQ with an acetylated N-terminus, corresponding to residues 17–23 of thymosin beta-4.

Is TB-500 the same as thymosin beta-4?

No. Thymosin beta-4 is a 43-amino-acid protein of about 4.9 kDa that occurs naturally in almost all cells. TB-500 reproduces only a short active segment of it. Results obtained with full-length thymosin beta-4 cannot automatically be attributed to TB-500.

What does thymosin beta-4 do in cells?

Its best-established role is sequestering monomeric (G-) actin, which regulates actin polymerisation and cell motility. Research has also mapped other activities to short sequences, including an anti-inflammatory and anti-fibrotic N-terminal tetrapeptide, Ac-SDKP.

What is TB-500 fragment 17-23?

It refers to the same LKKTETQ region: amino acids 17–23 of thymosin beta-4, the central actin-binding domain. TB-500 products are typically based on this region.

How is TB-500 detected analytically?

By liquid chromatography–mass spectrometry. A doping-control method identified N-acetylated LKKTETQ and its metabolites in equine urine and plasma after characterising metabolites in vitro.

References

Ho EN, et al. Doping control analysis of TB-500, a synthetic version of an active region of thymosin β₄, in equine urine and plasma by liquid chromatography-mass spectrometry. J Chromatogr A. 2012. PMID: 23084823 https://pubmed.ncbi.nlm.nih.gov/23084823/
Sosne G, et al. Biological activities of thymosin beta4 defined by active sites in short peptide sequences. FASEB J. 2010. PMID: 20179146 https://pubmed.ncbi.nlm.nih.gov/20179146/
Hannappel E. beta-Thymosins. Ann N Y Acad Sci. 2007. PMID: 17468232 https://pubmed.ncbi.nlm.nih.gov/17468232/
Bubb MR. Thymosin beta 4 interactions. Vitam Horm. 2003. PMID: 12852258 https://pubmed.ncbi.nlm.nih.gov/12852258/
Goldstein AL, et al. Advances in the basic and clinical applications of thymosin β4. Expert Opin Biol Ther. 2015. PMID: 26096726 https://pubmed.ncbi.nlm.nih.gov/26096726/
PubChem Compound Summary for CID 45382195, Thymosin beta-4. National Center for Biotechnology Information. https://pubchem.ncbi.nlm.nih.gov/compound/45382195