Thymosin Beta-4 (Tβ4): Compound Reference for Researchers

A neutral reference sheet for thymosin beta-4: its structure, what it is known to do at the molecular level, how it is characterised in the laboratory, and how the name “TB-500” relates to it.

At a glance

Property	Value
Names	Thymosin beta-4, thymosin β4, Tβ4, TB4, TB-4. Sold by some suppliers under the name “TB-500” (see the naming note below).
Class	Naturally occurring 43-amino-acid peptide (a β-thymosin); N-terminally acetylated
Gene	TMSB4X (human)
Sequence	Ac-SDKPDMAEIEKFDKSKLKKTETQEKNPLPSKETIEQEKQAGES (Ac = N-terminal acetyl group)
Molecular weight	≈ 4963.5 g/mol (average) for the acetylated 43-residue peptide; monoisotopic mass ≈ 4960.49 Da
Composition	Rich in lysine (9) and glutamic acid (8); one methionine, one phenylalanine; no cysteine, tryptophan or tyrosine
Form supplied	Lyophilized powder
Regulatory status	Supplied for laboratory research only; not an approved drug product. Thymosin β4 and its derivatives have appeared on the World Anti-Doping Agency Prohibited List (check the current list).

Sequence and annotation are from the UniProt record for human thymosin beta-4 (P62328). Masses are calculated from the sequence and should be compared with the laboratory’s own mass-spectrometry result for the lot you hold.

What it is

Thymosin beta-4 is a small, highly conserved protein found in most animal cells. It was first isolated from thymus tissue, which is where the “thymosin” name comes from, but it is expressed widely. In the cell, its best-characterised role is binding actin: it sequesters monomeric (G-) actin and so helps regulate how actin filaments form. This activity is carried by a short actin-binding region of the peptide, annotated as a β-thymosin (WH2-type) domain, in which individual residues such as lysine-12 have been shown by mutation to be needed for binding (references 1, 3, 7).

The peptide is processed after it is made: the initiator methionine is removed and the new N-terminal serine is acetylated. That acetyl group is part of the natural molecule and is visible in mass spectrometry (reference 2).

A note on the name “TB-500”

The name is not used consistently. In the anti-doping and sports-science literature, “TB-500” generally refers to a short synthetic fragment of thymosin β4 (the seven residues LKKTETQ, positions 17–23 of the mature peptide), whereas thymosin β4 itself is the full-length 43-residue peptide described on this page. Our product page and certificate refer to thymosin beta-4 (TB-4). Whatever name appears on a label, check which molecule the laboratory’s report says was tested.

What the published literature looks like

Published work on thymosin β4 spans basic cell biology, protein chemistry and a wide range of preclinical studies. Reviews cover its biochemistry and post-translational modifications (references 1 and 2), its binding to actin (reference 3), and its study in models of dermal healing (reference 4) and the heart (reference 5). A 2026 review in Sports Medicine examines the safety and efficacy evidence for approved and unapproved peptide therapies in musculoskeletal injury and athletic performance (reference 6).

These are cited to show the breadth of the literature, not to endorse any conclusion in it.

How to read the evidence

• Know which molecule a study used. Findings for full-length thymosin β4 do not automatically apply to fragments, and vice versa. Because of the naming issue above, this is worth checking in every paper.
• Laboratory results are not human results. Studies in cells and animal models do not establish effects, safety or appropriate use in people.
• Material quality matters. Results depend on the peptide being what the label says, adequately pure, and correctly handled. That is the purpose of the analytical documentation below.

Analytical notes

These points follow from the sequence and are useful when reading a certificate for this compound (see our guides to reading a COA and to HPLC and mass spectrometry).

• Detection wavelength. The sequence has one phenylalanine and no tryptophan or tyrosine, so it absorbs very little at 280 nm. HPLC is normally monitored at about 214–220 nm. Our certificate for lot TB062026-01 reports the chromatogram at 220 nm.
• Mass check. At roughly 4.96 kDa the peptide carries several charges in electrospray mass spectrometry. Expected average-mass ions include about m/z 993.7 (5+), 828.3 (6+), 710.1 (7+) and 621.4 (8+), which software converts to a single molecular mass near 4963.5 Da. A species about 42 Da lighter would correspond to the non-acetylated peptide.
• Chemistry. The sequence contains one methionine, which can oxidise (about +16 Da), and one asparagine and three glutamines, which can deamidate (about +1 Da). It is very hydrophilic and highly charged (nine lysines, eight glutamates, three aspartates), so it tends to elute early in reversed-phase HPLC.
• Identity. Our certificate for this lot reports FTIR confirming the presence of TB-4 together with excipients. FTIR is a fingerprint comparison; mass spectrometry confirms the molecular mass.

Handling and storage

General laboratory guidance for lyophilized peptides applies: store cold, dry, sealed and protected from light, let the vial reach room temperature before opening, and avoid repeated freeze–thaw cycles for any solution. Because the sequence contains a methionine, limiting exposure to air and light is sensible. Details are in our guide to research peptide storage and stability.

HLX Peptide documentation

• Product: TB-500 (Thymosin Beta-4), 10 mg
• Certificate: lot TB062026-01, tested June 8, 2026 by BT Labs. The batch record and the full PDF are on the product page, and every report is listed on our certificates of analysis page.
• Our process: Quality & Testing
• Related reference: BPC-157: Compound Reference
• Related blends: BPC-157 / TB-500 blend · KLOW blend · GLOW blend

References

1. Hannappel E. β-Thymosins. Ann N Y Acad Sci. 2007;1112:21–37. PMID 17468232.
2. Hannappel E. Thymosin beta4 and its posttranslational modifications. Ann N Y Acad Sci. 2010;1194:27–35. PMID 20536447.
3. Ying Y, et al. Thymosin beta4 and Actin: Binding Modes, Biological Functions and Clinical Applications. Curr Protein Pept Sci. 2023;24(1):78–88. PMID 36464872.
4. Kleinman HK, et al. Thymosin beta4 Promotes Dermal Healing. Vitam Horm. 2016;102:251–275. PMID 27450738.
5. Hinkel R, et al. Thymosin beta4-mediated protective effects in the heart. Expert Opin Biol Ther. 2018;18(sup1):121–129. PMID 30063857.
6. Mendias CL, et al. Safety and Efficacy of Approved and Unapproved Peptide Therapies for Musculoskeletal Injuries and Athletic Performance. Sports Med. 2026;56(8):1921–1935. PMID 41966639.
7. UniProt Knowledgebase, entry P62328 (TYB4_HUMAN), thymosin beta-4: uniprot.org/uniprotkb/P62328. Masses calculated from the sequence.
8. World Anti-Doping Agency, Prohibited List: wada-ama.org/en/prohibited-list.

Last reviewed October 5, 2026. All products are sold strictly for laboratory research use only. Not for human or veterinary use, and not a drug, food, or cosmetic.