Thymosin alpha-1 and thymosin beta-4 are often assumed to be versions of the same molecule. They are not. The shared word thymosin is a historical label from the 1970s, when researchers isolated a mixture of peptides from calf thymus and named its components by their position on an electrophoresis gel. Thymosin alpha-1 and thymosin beta-4 came out of that same extract, but they differ in sequence, size, origin and research focus. This article sets out the differences.
For laboratory research use only. Not for human or veterinary use. See our research use only policy.
Thymosin beta-4 is the parent of the peptide sold as TB-500, so this article sits within our BPC-157 and TB-500 research overview cluster.
At a glance: thymosin alpha-1
- Name: Thymosin alpha-1
- Synonyms: thymalfasin, Talpha1
- Sequence: Ac-Ser-Asp-Ala-Ala-Val-Asp-Thr-Ser-Ser-Glu-Ile-Thr-Thr-Lys-Asp-Leu-Lys-Glu-Lys-Lys-Glu-Val-Val-Glu-Glu-Ala-Glu-Asn
- Molecular formula: C129H215N33O55
- Molecular weight: 3108.3 g/mol
- CAS number: 62304-98-7
- Form: Lyophilised powder
- Storage: 2-8°C, dark, upright, do not freeze. Keep sealed until use.
At a glance: thymosin beta-4 (TB-500)
- Name: TB-500 (thymosin beta-4 related peptide)
- Synonyms: thymosin beta-4 fragment
- Sequence: commonly described as Ac-LKKTETQ, residues 17 to 23 of the 43-residue 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.
Where the thymosin name comes from
In the 1960s and 1970s, Allan Goldstein and colleagues prepared a partially purified extract of calf thymus known as thymosin fraction 5. It contained dozens of small peptides. Individual components were named according to their isoelectric behaviour: alpha peptides were the more acidic fractions and beta peptides less so. Thymosin alpha-1 was isolated and sequenced from this material in 1977, and thymosin beta-4 was sequenced in 1981.
Later work showed that the shared origin was a coincidence of method rather than biology. The two peptides are encoded by different genes, belong to different protein families and are found in different cellular contexts.
Thymosin alpha-1 in detail
Thymosin alpha-1 is a 28-residue peptide with an acetylated N-terminus. It is derived from a larger precursor, prothymosin alpha, by cleavage of the N-terminal region. The sequence is strongly acidic, with numerous glutamic and aspartic acid residues, and the peptide is largely unstructured in water.
Research on thymosin alpha-1 has focused on immunology. Work in cell and animal models has investigated its interaction with dendritic cells and T-cell maturation, including a 2004 study by Romani and colleagues that reported activation of dendritic cells through toll-like receptor signalling in mouse models of fungal infection.
Regulatory status
A synthetic form of thymosin alpha-1, given the international non-proprietary name thymalfasin, has been approved as a medicine in a number of countries outside the UK. It is not an authorised medicine in the UK. Our thymosin alpha-1 is a research chemical, not a medicine, and is supplied for laboratory use only.
Thymosin beta-4 in detail
Thymosin beta-4 is a 43-residue peptide, also N-terminally acetylated, and one of the most abundant members of the beta-thymosin family. Its principal known role is binding monomeric G-actin and sequestering it from filament assembly. It is present in most nucleated mammalian cells and in platelets, which explains why its research literature spans cell migration, cytoskeletal biology and tissue injury models in rodents.
The peptide sold as TB-500 is usually described as a short acetylated fragment of the thymosin beta-4 actin-binding region, though the name has also been applied to the full-length protein. Our explainer on what TB-500 is covers this in detail.
Key differences summarised
- Size: thymosin alpha-1 has 28 residues. Thymosin beta-4 has 43, and the TB-500 fragment usually seven.
- Precursor: thymosin alpha-1 is cleaved from prothymosin alpha. Thymosin beta-4 is expressed as its own gene product.
- Family: thymosin alpha-1 relates to the prothymosin family. Thymosin beta-4 belongs to the beta-thymosins, alongside beta-10 and beta-15.
- Research focus: thymosin alpha-1 work centres on immune signalling. Thymosin beta-4 work centres on actin and cell migration.
- Regulatory status: thymalfasin is approved in some countries outside the UK. Thymosin beta-4 has no approved medicine form.
Why the distinction matters in the lab
Because the names are similar, it is easy to order or record the wrong material. Mass spectrometry provides a quick check: thymosin alpha-1 has a molecular weight of about 3108.3 g/mol, distinct from both the TB-500 fragment and full-length thymosin beta-4. HPLC purity should also be confirmed, and our catalogue specification is >99% by HPLC. Our guide to reading a peptide certificate of analysis explains both checks.
Both peptides are supplied lyophilised. We recommend 2-8°C, protected from light, upright and not frozen, with the vial sealed until use.
View thymosin alpha-1 or TB-500 in the catalogue.
Frequently asked questions
Are thymosin alpha-1 and thymosin beta-4 related?
Only by name. Both were first isolated from the same calf thymus extract, but they are encoded by different genes, belong to different families and have unrelated sequences.
What is the CAS number for thymosin alpha-1?
The CAS number for thymosin alpha-1 is 62304-98-7. Its molecular formula is C129H215N33O55 and its molecular weight is about 3108.3 g/mol.
Is TB-500 a form of thymosin alpha-1?
No. TB-500 relates to thymosin beta-4. It has no structural relationship to thymosin alpha-1.
Is thymosin alpha-1 an approved medicine in the UK?
No. A synthetic form called thymalfasin has been approved in some countries outside the UK, but it is not authorised in the UK. Our material is a research chemical, not a medicine.
How many amino acids does thymosin alpha-1 have?
Thymosin alpha-1 has 28 amino acids with an acetylated N-terminus. Thymosin beta-4 has 43.
References
- Goldstein AL, Low TL, McAdoo M, et al. Thymosin alpha1: isolation and sequence analysis of an immunologically active thymic polypeptide. Proceedings of the National Academy of Sciences USA, 1977.
- Low TL, Hu SK, Goldstein AL. Complete amino acid sequence of bovine thymosin beta 4. Proceedings of the National Academy of Sciences USA, 1981.
- Romani L, Bistoni F, Gaziano R, et al. Thymosin alpha 1 activates dendritic cells for antifungal Th1 resistance through toll-like receptor signaling. Blood, 2004.
- 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.
For laboratory research use only. Not for human or veterinary use. See our research use only policy.