What is TB-500? It is a name used in the research chemical market for a synthetic peptide related to thymosin beta-4, a small protein found in almost every mammalian cell. The term tb 500 is not an official drug name, and it has been applied to more than one molecule, which is the source of much confusion. This article explains the parent protein, the fragment most often meant by the name and how a laboratory can confirm what it actually has.
For laboratory research use only. Not for human or veterinary use. See our research use only policy.
For the wider context, including how TB-500 compares with BPC-157, see our BPC-157 and TB-500 research overview.
At a glance
- Name: TB-500
- Synonyms: thymosin beta-4 fragment, Ac-LKKTETQ (commonly cited form)
- Sequence: commonly described as the acetylated fragment Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln, corresponding to residues 17 to 23 of thymosin beta-4; confirm against analytical data
- Molecular formula: confirm from the analytical data for the specific material
- Molecular weight: confirm from the analytical data for the specific material
- CAS number: 885340-08-9
- Form: Lyophilised powder
- Storage: 2-8°C, dark, upright, do not freeze. Keep sealed until use.
Thymosin beta-4: the parent protein
Thymosin beta-4 is a 43-amino-acid peptide with an acetylated N-terminus. It was first sequenced from calf thymus by Low, Hu and Goldstein in 1981, as part of a wider programme investigating thymus-derived peptides known collectively as thymosins. Despite the name, later work showed that thymosin beta-4 is not specific to the thymus. It is present at high concentrations in many cell types, including platelets and white blood cells.
Its main known function was clarified in 1991, when Safer and colleagues showed that thymosin beta-4 was identical to a previously described actin-sequestering peptide. It binds monomeric G-actin in a one-to-one complex and prevents it from polymerising into filaments. Because the actin cytoskeleton controls cell shape, division and migration, a protein that buffers the free actin pool sits at the centre of many cellular processes. That is one reason thymosin beta-4 attracted research interest well beyond immunology.
The beta-thymosin family
Thymosin beta-4 belongs to a family of closely related beta-thymosins, including thymosin beta-10 and beta-15, which share a conserved actin-binding motif. The review by Huff and colleagues (2001) describes this family and the shared structural features in detail. The beta-thymosins are unrelated to thymosin alpha-1, which is discussed in our article on thymosin alpha-1 vs thymosin beta-4.
The fragment most often called TB-500
Within the 43 residues of thymosin beta-4 is a short central stretch, LKKTETQ (residues 17 to 23), that forms part of the actin-binding region. Research has investigated whether this motif alone reproduces some activities of the full protein in cell and animal models. The synthetic peptide most often sold as TB-500 is an N-terminally acetylated version of this stretch.
However, the name has also been used for synthetic full-length thymosin beta-4, and some older references use the two names interchangeably. They are not. A seven-residue fragment and a 43-residue protein differ by several thousand daltons in mass and cannot be assumed to behave the same way in an experiment. For that reason we list the molecular formula and weight as values to confirm from the analytical data, rather than quoting a figure that may describe a different molecule.
Confirming identity in the lab
- Mass spectrometry: the observed mass immediately distinguishes a short fragment from the full-length protein.
- HPLC: confirms that the main peak dominates the chromatogram. Our catalogue purity specification is >99% by HPLC.
- Documentation: compare the sequence and mass on the analytical report with the form your study design requires.
Our guide on how to read a peptide certificate of analysis explains these checks in more depth.
What has thymosin beta-4 research examined?
The published literature on thymosin beta-4 comes from many independent groups. Reviews, including Goldstein, Hannappel and Kleinman (2005), summarise work in cell culture on actin dynamics and cell migration, and work in rodent models of skin, corneal and cardiac tissue injury. Some studies used full-length protein, while others used fragments such as the actin-binding region or the N-terminal tetrapeptide Ac-SDKP, which has a distinct literature of its own.
Full-length thymosin beta-4 has also been examined in early-phase clinical trials of investigational ophthalmic and dermal formulations sponsored by drug developers. Those are separate investigational products. Thymosin beta-4 is not an authorised medicine in the UK, and research-grade TB-500 is not a medicine.
TB-500 compared with BPC-157
TB-500 is frequently paired with BPC-157, a 15-residue synthetic peptide with an entirely different origin. The two share overlapping research themes in rodent models but have no structural relationship. Our BPC-157 vs TB-500 comparison sets out the differences in sequence, origin and literature.
Storage
TB-500 is supplied as a lyophilised powder. We recommend storage at 2-8°C, protected from light, upright and not frozen, with the vial sealed until use. Letting a chilled vial reach room temperature before opening limits condensation. See how to store lyophilised peptides for the reasoning.
View TB-500 in the catalogue.
Frequently asked questions
Is TB-500 the same as thymosin beta-4?
Not necessarily. Thymosin beta-4 is a 43-residue protein. TB-500 is a market name most often used for a short acetylated fragment of its actin-binding region, though it has also been used for the full-length synthetic protein. Mass spectrometry data confirm which form a material is.
What does thymosin beta-4 do in cells?
Its best characterised role is binding monomeric G-actin and sequestering it, which regulates the pool of actin available for filament assembly. This was established in biochemical studies in the early 1990s.
What is the CAS number for TB-500?
The CAS number listed for our TB-500 is 885340-08-9.
Is TB-500 an approved medicine?
No. Neither TB-500 nor thymosin beta-4 is an authorised medicine in the UK. Our material is supplied for laboratory research use only.
How is TB-500 different from thymosin alpha-1?
They are unrelated peptides. Thymosin alpha-1 is a 28-residue peptide derived from prothymosin alpha, while TB-500 relates to the beta-thymosin family. They share a name only because both were first isolated from thymus extracts.
References
- Low TL, Hu SK, Goldstein AL. Complete amino acid sequence of bovine thymosin beta 4. Proceedings of the National Academy of Sciences USA, 1981.
- Safer D, Elzinga M, Nachmias VT. Thymosin beta 4 and Fx, an actin-sequestering peptide, are indistinguishable. Journal of Biological Chemistry, 1991.
- Huff T, Muller CS, Otto AM, Netzker R, Hannappel E. beta-Thymosins, small acidic peptides with multiple functions. International Journal of Biochemistry and Cell Biology, 2001.
- Goldstein AL, Hannappel E, Kleinman HK. Thymosin beta4: actin-sequestering protein moonlights to repair injured tissues. Trends in Molecular Medicine, 2005.
For laboratory research use only. Not for human or veterinary use. See our research use only policy.