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TB-500 vs Thymosin Beta-4: Fragment, Full Protein, and Why the Name Is Confusing

By The Bionova Club Team

Research use only. Bionova products are sold strictly for in-vitro and laboratory research by qualified professionals. They are not drugs, food, or cosmetics, are not approved by the FDA, and are not for human or veterinary use. Nothing in this article is medical advice or a claim about effects in people.

Disclosure: Bionova Club sells TB-500 and a BPC-157 + TB-500 blend, both linked below.

Search for "TB-500" and you will find it described as thymosin beta-4, as a fragment of thymosin beta-4, and as a "synthetic version" of it, sometimes all on the same page. Those are not the same thing. Thymosin beta-4 (Tβ4) is a 43-amino-acid protein. In the scientific literature, "TB-500" has been used for a much shorter synthetic peptide based on one region of that protein. Bionova's TB-500 product, by contrast, is identified as the full-length molecule.

This guide sorts out the names, compares the sequences, and explains how to tell which molecule a given source means.

What is thymosin beta-4?

Thymosin beta-4 is a small, highly acidic protein first purified from calf thymus as part of a mixture called thymosin fraction 5. Its complete amino acid sequence was published in 1981: 43 residues, a molecular weight of 4,982, and an N-terminus blocked by an acetyl group (Low et al., 1981, PNAS).

Despite the "thymosin" name, Tβ4 turned out to be found in many cell types. It belongs to the β-thymosin family of small acidic peptides (Huff et al., 2001, International Journal of Biochemistry & Cell Biology). Its best-characterized molecular role is binding monomeric (G-) actin. Safer and colleagues showed that Tβ4 is the same molecule as "Fx," a previously described actin-sequestering peptide (Safer et al., 1991, Journal of Biological Chemistry). In resting human leukocytes, Tβ4 was found to sequester most of the unpolymerized actin (Cassimeris et al., 1992, Journal of Cell Biology).

The full sequence (one-letter code, N-terminal acetyl group shown as Ac-) is:

Ac-SDKPDMAEIEKFDKSKLKKTETQEKNPLPSKETIEQEKQAGES

What is TB-500 in the scientific literature?

In peer-reviewed work, "TB-500" shows up mostly in anti-doping chemistry. A 2012 analytical paper on detecting TB-500 in equine samples describes it as a preparation whose key ingredient is the peptide LKKTETQ with an artificially acetylated N-terminus (Ho et al., 2012, Journal of Chromatography A). The same paper identifies LKKTETQ as residues 17 to 23 of Tβ4, the region associated with actin binding.

So, in that literature, TB-500 is a seven-residue fragment (Ac-LKKTETQ), not the 43-residue protein.

TB-500 vs thymosin beta-4 at a glance

  • Length
    • Thymosin beta-4 (full length): 43 amino acids
    • Ac-LKKTETQ ("TB-500" in anti-doping literature): 7 amino acids
  • Sequence
    • Thymosin beta-4 (full length): Ac-SDKPDMAEIEKFDKSKLKKTETQEKNPLPSKETIEQEKQAGES
    • Ac-LKKTETQ ("TB-500" in anti-doping literature): Ac-LKKTETQ
  • Relationship
    • Thymosin beta-4 (full length): Native protein
    • Ac-LKKTETQ ("TB-500" in anti-doping literature): Synthetic peptide matching Tβ4 residues 17–23
  • Molecular formula
  • Molecular weight
    • Thymosin beta-4 (full length): ~4,963 g/mol (PubChem computed average molecular weight; the 1981 sequencing paper reported 4,982)
    • Ac-LKKTETQ ("TB-500" in anti-doping literature): ~889 g/mol (PubChem)
  • First described
    • Thymosin beta-4 (full length): Sequence published 1981
    • Ac-LKKTETQ ("TB-500" in anti-doping literature): Described in doping-control literature, 2012

The full-length weight above is the average molecular weight PubChem computes from the formula C₂₁₂H₃₅₀N₅₆O₇₈S (CID 45382195; monoisotopic mass ~4,960.5 Da). The 1981 sequencing paper on the bovine protein reported a molecular weight of 4,982 (Low et al., 1981). The heptapeptide formula and weight are from PubChem CID 62707662.

Which one is Bionova's TB-500?

Bionova's TB-500 10 mg product page identifies the product as thymosin beta-4 and references PubChem CID 45382195. That PubChem record, for full-length thymosin beta-4 rather than the seven-residue fragment, gives the molecular formula C₂₁₂H₃₅₀N₅₆O₇₈S (PubChem, thymosin beta 4, CID 45382195). The vial is labeled 10 mg. In other words, Bionova uses "TB-500" as the familiar product name for the full-length 43-residue sequence.

That difference between a product name and the literature usage is why the names are confusing. When reading any source, check the sequence or formula rather than the name alone.

Why the name causes confusion

Three things blur the picture:

  1. One name, two molecules. "TB-500" can mean the short Ac-LKKTETQ peptide (in doping-control papers) or full-length Tβ4 (in many product listings).
  2. Fragments with their own names. Tβ4 is also the precursor of Ac-SDKP, the N-terminal tetrapeptide (Ac-Ser-Asp-Lys-Pro). Grillon and colleagues showed that Ac-SDKP can be generated from Tβ4 by a single enzymatic cleavage between Pro4 and Asp5 (Grillon et al., 1990, FEBS Letters). Ac-SDKP has a separate literature of its own.
  3. Literature on the protein is not literature on a fragment. Most published Tβ4 research uses the full-length protein. Findings for the 43-residue molecule cannot be assumed to apply to a seven-residue peptide, or the reverse.

TB-500 vs thymosin alpha 1

"Thymosin alpha 1" is a frequent autocomplete pairing, but it is unrelated in structure. Both names come from the same historical thymus extract, thymosin fraction 5, and a shared naming scheme was proposed for its components (Goldstein et al., 1977, PNAS).

  • Length
    • Thymosin alpha 1: 28 amino acids
    • Thymosin beta-4: 43 amino acids
  • Origin
    • Thymosin alpha 1: N-terminal portion of prothymosin alpha (~112 residues)
    • Thymosin beta-4: Isolated as a 43-residue peptide
  • Family
    • Thymosin alpha 1: α-thymosins
    • Thymosin beta-4: β-thymosins
  • Best-known molecular role
    • Thymosin alpha 1: Studied in immunology research
    • Thymosin beta-4: Actin monomer binding

Thymosin alpha 1 was sequenced in 1977 (Goldstein et al., 1977). It was later found at the N-terminus of a larger precursor, prothymosin alpha (Haritos et al., 1984, PNAS). The two share a "thymosin" label and nothing else of substance.

TB-500 in blends

TB-500 also appears in pre-blended research vials. Bionova's BPC-157 + TB-500 blend, sold under the Wolverine name, lists 10 mg of each component on its product page. BPC-157 is an unrelated 15-residue peptide with its own literature. Our BPC-157 vs TB-500 research overview compares the two molecules, and GLOW vs KLOW vs Wolverine compares the multi-peptide blends that include TB-500. The copper peptide in GLOW and KLOW is covered in our GHK-Cu research overview. For background on peptide terminology in general, see What are peptides? A primer for researchers.

Storage notes for lyophilized TB-500

  • Keep it sealed, cold and dry. Store the lyophilized powder in its original sealed vial, away from light and moisture.
  • Warm before opening. Let a sealed vial reach room temperature before opening so moisture does not condense on the powder.
  • Follow the label. Store as directed on the product label.

Key takeaways

  • Thymosin beta-4 is a 43-residue, N-terminally acetylated protein whose sequence was published in 1981. Its best-characterized role is binding actin monomers.
  • In anti-doping literature, "TB-500" refers to Ac-LKKTETQ, a seven-residue synthetic peptide matching Tβ4 residues 17–23.
  • Bionova uses "TB-500" as the product name for full-length Tβ4. Its product page identifies the product as thymosin beta-4, and PubChem gives the full-length formula as C₂₁₂H₃₅₀N₅₆O₇₈S (CID 45382195).
  • Thymosin alpha 1 is a different, 28-residue peptide that only shares the "thymosin" name.
  • Always confirm the sequence or formula, not just the name.

Frequently asked questions

Is TB-500 the same as thymosin beta-4?

It depends on who is using the name. In doping-control literature, TB-500 means the short acetylated peptide LKKTETQ, a fragment of Tβ4. Bionova uses TB-500 as the product name for full-length thymosin beta-4: its TB-500 page identifies the product as thymosin beta-4 (PubChem CID 45382195).

What is TB4?

TB4 or Tβ4 is shorthand for thymosin beta-4, the 43-amino-acid β-thymosin protein.

What part of thymosin beta-4 is LKKTETQ?

LKKTETQ corresponds to residues 17 to 23 of thymosin beta-4, a region associated with actin binding.

Is TB-500 related to thymosin alpha 1?

No. Thymosin alpha 1 is a 28-residue peptide from a different family. The two were named from the same historical thymus extract but are structurally unrelated.

How should lyophilized TB-500 be stored?

Keep the sealed vial cold, dry and away from light, let it reach room temperature before opening, and store it as directed on the product label.

Shop for your research: TB-500 or the Wolverine (BPC-157 + TB-500) blend, for laboratory research. Use code CLUB10 at checkout for 10% off.

References

  1. Low TL, Hu SK, Goldstein AL. Complete amino acid sequence of bovine thymosin beta 4: a thymic hormone that induces terminal deoxynucleotidyl transferase activity in thymocyte populations. Proc Natl Acad Sci U S A. 1981. https://pubmed.ncbi.nlm.nih.gov/6940133/
  2. Huff T, Müller CS, Otto AM, et al. beta-Thymosins, small acidic peptides with multiple functions. Int J Biochem Cell Biol. 2001. https://pubmed.ncbi.nlm.nih.gov/11311852/
  3. Safer D, Elzinga M, Nachmias VT. Thymosin beta 4 and Fx, an actin-sequestering peptide, are indistinguishable. J Biol Chem. 1991. https://pubmed.ncbi.nlm.nih.gov/1999398/
  4. Cassimeris L, Safer D, Nachmias VT, et al. Thymosin beta 4 sequesters the majority of G-actin in resting human polymorphonuclear leukocytes. J Cell Biol. 1992. https://pubmed.ncbi.nlm.nih.gov/1447300/
  5. Ho EN, et al. Doping control analysis of TB-500, a synthetic version of an active region of thymosin β4, in equine urine and plasma by liquid chromatography-mass spectrometry. J Chromatogr A. 2012. https://pubmed.ncbi.nlm.nih.gov/23084823/
  6. Grillon C, et al. Involvement of thymosin beta 4 and endoproteinase Asp-N in the biosynthesis of the tetrapeptide AcSerAspLysPro a regulator of the hematopoietic system. FEBS Lett. 1990. https://pubmed.ncbi.nlm.nih.gov/2253778/
  7. Goldstein AL, et al. Thymosin alpha1: isolation and sequence analysis of an immunologically active thymic polypeptide. Proc Natl Acad Sci U S A. 1977. https://pubmed.ncbi.nlm.nih.gov/265536/
  8. Haritos AA, Goodall GJ, Horecker BL. 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. https://pubmed.ncbi.nlm.nih.gov/6583693/
  9. PubChem. Thymosin beta 4, CID 45382195 (molecular formula and weight). https://pubchem.ncbi.nlm.nih.gov/compound/45382195

For laboratory research use only. Not for human consumption.