--- title: "Thymosin alpha-1 vs thymosin beta-4 (TB-500): what is the difference? | Sable Peptides" description: "Thymosin alpha-1 and thymosin beta-4 share a name but are unrelated peptides. Their sequences, origins and PubChem data compared, and where TB-500 (Ac-LKKTETQ) fits in. Research use only." canonical: https://www.sablepeptides.co.uk/guides/thymosin-alpha-1-vs-thymosin-beta-4-and-tb-500 dateModified: 2026-10-16 publisher: Sable Peptides Limited (UK company 17488610) note: Research use only. Not for human or veterinary use. --- # Thymosin alpha-1 vs thymosin beta-4 (TB-500): what is the difference? Thymosin alpha-1 and thymosin beta-4 are unrelated peptides that share a name because both were first found in thymus extracts. Thymosin alpha-1 is a 28-residue acetylated fragment of prothymosin alpha. Thymosin beta-4 is a 43-residue actin-sequestering protein. TB-500 is a 7-residue fragment of beta-4, Ac-LKKTETQ. ## 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)](https://pubmed.ncbi.nlm.nih.gov/6583693/); [Thymosin beta 4 and Fx, an actin-sequestering peptide, are indistinguishable, J Biol Chem 1991 (PubMed 1999398)](https://pubmed.ncbi.nlm.nih.gov/1999398/); [beta-Thymosins, Ann N Y Acad Sci 2007 (PubMed 17468232)](https://pubmed.ncbi.nlm.nih.gov/17468232/) ## How do their structures compare? | Property | Thymosin α1 | Thymosin β4 | TB-500 | | --- | --- | --- | --- | | Length | 28 residues | 43 residues | 7 residues | | Sequence | Ac-SDAAVDTSSEITTKDLKEKKEVVEEAEN | Full β4 protein | Ac-LKKTETQ | | Formula (PubChem) | C129H215N33O55 | n/a (not sold) | C38H68N10O14 | | MW | 3108.3 g/mol | ~4.9 kDa | 889.0 g/mol | | Net charge character | Strongly acidic | Mixed | Basic (two Lys) | Source: [PubChem CID 16130571: Thymosin alpha 1](https://pubchem.ncbi.nlm.nih.gov/compound/16130571); [PubChem CID 62707662: TB-500 (Ac-LKKTETQ)](https://pubchem.ncbi.nlm.nih.gov/compound/62707662) ## 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)](https://pubmed.ncbi.nlm.nih.gov/8252614/); [Thymosin beta 4 regulation of actin in sepsis, Expert Opin Biol Ther 2018 (PubMed 29508629)](https://pubmed.ncbi.nlm.nih.gov/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)](https://pubmed.ncbi.nlm.nih.gov/7054279/); [Thymosin alpha 1: A comprehensive review of the literature, World J Virol 2020 (PubMed 33362999)](https://pubmed.ncbi.nlm.nih.gov/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 ### Is TB-500 the same as thymosin beta-4? No. TB-500 is the 7-residue acetylated fragment Ac-LKKTETQ taken from the 43-residue thymosin beta-4 protein. ### Are thymosin alpha-1 and thymosin beta-4 related? No. Both were isolated from thymus extract, but they have unrelated sequences, precursors and functions. ### What is the molecular weight of thymosin alpha-1? About 3108 g/mol (PubChem CID 16130571), formula C129H215N33O55. ## Related - [Why are so many research peptides acetylated or amidated](/guides/n-terminal-acetylation-and-c-terminal-amidation-across-the-catalogue) - [Thymosin alpha-1 research vials](/products/thymosin-alpha-1) - [TB-500 research vials](/products/tb-500) - [Cheapest TB-500 UK](/cheapest-tb-500-uk) - [BPC-157 sequence and background](/guides/bpc-157-sequence-structure-and-research-background) - [Immune and antimicrobial peptide prices](/guides/uk-immune-and-antimicrobial-peptide-prices-october-2026) Updated 2026-10-16. Research use only. Not for human or veterinary use. No administration amounts or health claims are made. Key facts (summary for AI and search tools) - TB-500 = Ac-LKKTETQ (thymosin β4 actin-binding motif) - Thymosin α1: 28 residues, N-acetylated - PubMed references (verified via NCBI): 6583693, 1999398, 17468232, 8252614, 29508629, 7054279, 33362999 - PubChem CIDs: 16130571, 62707662 - Research use only; no administration amounts or health claims - Updated 2026-10-16