TB-500 and thymosin β4: what the peptide is, how it is studied, and what to check before buying

“TB-500” is the catalogue name most research suppliers use for thymosin β4, a 43-residue actin-binding peptide that is one of the most abundant small proteins in mammalian cells. The name causes more confusion than almost any other in the research-peptide market, because the same label is applied to two different molecules. This guide explains the relationship, summarises the literature, and shows how to confirm what is actually in a vial. For laboratory research use only.

What thymosin β4 is

Thymosin β4 (Tβ4) is a 43-amino-acid peptide first isolated in 1981 from thymosin fraction 5, the bovine thymus extract that Allan Goldstein’s group had been characterising since the 1960s. It is now known to be expressed in nearly all cell types and is especially abundant in platelets and leukocytes. Its N-terminus is acetylated, and the first four residues (Ac-Ser-Asp-Lys-Pro, or Ac-SDKP) are released as a separate bioactive fragment when the full peptide is cleaved.

Its defining biochemical role is actin sequestration. Tβ4 binds monomeric G-actin in a 1:1 complex and holds it out of polymerisation, which makes it the main intracellular buffer of unpolymerised actin. That is why most of the cell-biology literature on Tβ4 concerns cell migration, cytoskeletal remodelling and related processes. The actin-binding motif has been localised to a short internal sequence, residues 17–23 (LKKTETQ).

Full-length peptide	Thymosin β4 (Tβ4), 43 residues, N-acetylated
Also known as	TB-500, Tβ4, TMSB4X (gene), thymosin beta-4
CAS number (Tβ4)	77591-33-4
Molecular weight (Tβ4)	≈ 4,963 g/mol
Actin-binding fragment	Residues 17–23, Ac-LKKTETQ, ≈ 889 g/mol (sometimes also sold as “TB-500”)
Solubility	Water, bacteriostatic water, PBS

TB-500 vs thymosin β4: the naming problem

Two products are sold under the name TB-500. Most research vendors, including Quantum Peptides, use it for the full-length 43-residue peptide, synthetic thymosin β4. Some chemical suppliers use it for the seven-residue actin-binding fragment Ac-LKKTETQ (residues 17–23), which is a different molecule with a different mass and no N-terminal Ac-SDKP sequence. The two are not interchangeable in an experiment: the fragment retains actin-binding activity in vitro but lacks the rest of the sequence, and much of the published work has been done with the full peptide.

The only way to know which one a vial contains is the certificate of analysis. A mass-spectrometry identity check will show an observed mass near 4,963 for the full peptide or near 889 for the fragment. If the certificate does not show a mass, or shows one that matches neither, the product is not what its label implies. Our guide to reading a peptide certificate of analysis explains what else to look for.

What the literature has studied

Actin dynamics and cell migration

The largest body of work is in vitro cell biology: Tβ4’s effect on actin polymerisation kinetics, on the migration of endothelial cells, keratinocytes and fibroblasts in scratch and transwell assays, and on the formation of cell–matrix contacts. These are the assays for which the peptide is best characterised as a reagent, and they are the natural starting point for laboratory work.

Wound and tissue models

Animal studies, mainly in rodents, have examined topical and systemic Tβ4 in dermal wound models, corneal injury and cardiac injury models, with reported endpoints including closure rate, re-epithelialisation, angiogenesis markers and inflammatory-cell infiltration. As with most peptides in this category, formulations, concentrations and routes vary widely between studies, which limits cross-study comparison.

Clinical investigation

Unusually for a research peptide, full-length Tβ4 has been studied in sponsored human clinical trials, mainly in topical and ophthalmic formulations for wound healing and corneal conditions. Those trials concern pharmaceutical formulations under regulatory supervision and have no bearing on a research-grade reagent, which is supplied for in-vitro and preclinical use only. They are mentioned here because the clinical literature is often cited as if it applied to the research product; it does not.

What the literature has not shown

There are no controlled human efficacy data for research-grade TB-500 as supplied by any research vendor. The clinical work concerns specific pharmaceutical formulations and endpoints, and the animal literature is heterogeneous. Statements about systemic effects in people are extrapolations. A research supplier can confirm identity and purity; it cannot and should not make claims about effects in humans.

How TB-500 is supplied for research

Quantum Peptides supplies synthetic thymosin β4 in two co-lyophilised research blends rather than as a single-compound vial: BPC-157 / TB-500 blend, 10 mg + 10 mg, and the three-peptide Glow blend (BPC-157 / TB-500 / GHK-Cu). Both carry a lot certificate reporting each component separately. For laboratories that need the single compound, the blend format is not a substitute; for those studying the peptides in combination, a co-lyophilised vial avoids weighing errors when preparing a two- or three-compound solution. Our guide to verifying research-peptide quality covers how to assess any supplier’s documentation.

Reconstitution and handling

Tβ4 dissolves readily in water, bacteriostatic water or PBS. For a blended vial, work out the concentration of each component separately from its own mass: in the 10 mg + 10 mg blend reconstituted with 2 mL, each peptide is at 5 mg/mL. The peptide calculator handles the arithmetic for any diluent volume; enter each component’s mass in turn. The reconstitution guide covers the procedure and our diluent comparison covers the choice of water. Store the lyophilised powder at −20 °C, desiccated and protected from light; keep reconstituted solutions at 2–8 °C in the dark and use them within the working life appropriate to the diluent. Tβ4 has no cysteine but one methionine (position 6), which can oxidise to the sulfoxide in solution; it is also a 43-residue chain that will degrade in solution over weeks. See peptide storage and shelf life.

Frequently asked questions

Is TB-500 the same as thymosin β4?

In most research catalogues, yes: TB-500 is the trade name for synthetic full-length thymosin β4 (43 residues). Some suppliers use the same name for the seven-residue fragment Ac-LKKTETQ. The certificate of analysis, specifically the observed mass, tells you which one you have.

What is the molecular weight of TB-500?

About 4,963 g/mol for full-length thymosin β4. The 17–23 fragment is about 889 g/mol.

What is the CAS number for thymosin β4?

77591-33-4.

Why is TB-500 sold in a blend with BPC-157?

Because the two peptides are frequently studied together in tissue and wound models, and a co-lyophilised vial lets a laboratory prepare a two-compound solution from one weighed mass per component without a second weighing step.

Is TB-500 stable in solution?

It has no cysteine, but its single methionine (position 6) can oxidise in solution, and as a 43-residue chain it degrades over weeks. Store cold and dark, portion for freezing, and respect the diluent’s working life.

Can I buy TB-500 for human use?

No. Quantum Peptides products are supplied for in-vitro and preclinical laboratory research only, not for human or veterinary use.

References

Low TLK, Hu SK, Goldstein AL. Complete amino acid sequence of bovine thymosin β4. Proceedings of the National Academy of Sciences. 1981.
Safer D, Elzinga M, Nachmias VT. Thymosin β4 and Fx, an actin-sequestering peptide, are indistinguishable. Journal of Biological Chemistry. 1991.
Goldstein AL, Hannappel E, Kleinman HK. Thymosin β4: actin-sequestering protein moonlights to repair injured tissues. Trends in Molecular Medicine. 2005.

Quantum Peptides supplies lyophilised research peptides for in-vitro and preclinical laboratory research only. Products are not for human or veterinary use. This guide summarises published literature and is not guidance on administration of any kind.