Thymosin alpha-1 vs thymosin beta-4 (TB-500): what is the difference?

Why do two unrelated peptides share the name thymosin?

'Thymosin' was first applied to a crude calf-thymus extract (thymosin fraction 5). Individual peptides isolated from it were named by their position on electrophoresis (alpha, beta), not by family. So thymosin alpha-1 and the beta-thymosins share a name, not an ancestry.

Thymosin alpha-1 turned out to be the N-terminal part of a larger protein, prothymosin alpha. Thymosin beta-4 was later shown to be the main actin-monomer-sequestering peptide in many cells.

Source: Prothymosin alpha: isolation and properties of the major immunoreactive form of thymosin alpha 1 in rat thymus, Proc Natl Acad Sci U S A 1984 (PubMed 6583693); Thymosin beta 4 and Fx, an actin-sequestering peptide, are indistinguishable, J Biol Chem 1991 (PubMed 1999398); beta-Thymosins, Ann N Y Acad Sci 2007 (PubMed 17468232)

How do their structures compare?

Source: PubChem CID 16130571: Thymosin alpha 1; PubChem CID 62707662: TB-500 (Ac-LKKTETQ)

Where does TB-500's sequence come from?

LKKTETQ is the central actin-binding motif of thymosin beta-4. The research peptide carries an N-terminal acetyl group, so it is a short synthetic fragment of beta-4, not the whole protein. Structural studies of beta-4 and actin explain why this stretch matters for binding.

Source: How profilin promotes actin filament assembly in the presence of thymosin beta 4, Cell 1993 (PubMed 8252614); Thymosin beta 4 regulation of actin in sepsis, Expert Opin Biol Ther 2018 (PubMed 29508629)

What research literature exists for each?

Thymosin alpha-1 has a long immunology literature going back to radioimmunoassay work in the early 1980s, and broad reviews exist. Thymosin beta-4 research centres on actin dynamics and cell motility. Fragment-specific literature on TB-500 itself is much thinner than for the parent protein.

Source: Immunochemical studies on thymosin: radioimmunoassay of thymosin alpha 1, J Immunol 1982 (PubMed 7054279); Thymosin alpha 1: A comprehensive review of the literature, World J Virol 2020 (PubMed 33362999)

Sourcing note

Sable lists Thymosin alpha-1: 5 mg at £17.93; 10 mg at £27.98; TB-500: 2 mg at £14.26; 5 mg at £13.93; 10 mg at £10.99; 20 mg at £39.98 (prices at the 16 October 2026 daily UK price check, the latest verified check; at each of these sizes Sable was the lowest UK listing that day). Lowest UK price guaranteed, confirmed by daily price checks.

Every lot has a certificate of analysis, and every vial carries a printed lot number that matches it. Supplied for laboratory research use only.

Frequently asked questions