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What Is TB-500, Really? Full Thymosin Beta-4 vs the LKKTETQ Fragment
Few names in the research peptide world cause as much confusion as TB-500. It sounds like one defined molecule, but the label has been applied to different things by different sellers. Knowing what the possibilities are is the best protection against buying the wrong one.
Key takeaways
- Thymosin beta-4 is a natural 43-amino-acid peptide with a mass near 4963 daltons.
- Its actin-binding region includes the short stretch LKKTETQ, at positions 17 to 23.
- TB-500 is sometimes used to mean the full peptide and sometimes a shorter synthetic fragment.
- The only way to know is the sequence and the measured mass on the lab report.
- A 7-residue fragment weighs under 1,000 daltons, so mass separates the two cases at once.
The natural molecule
Thymosin beta-4 was first isolated from calf thymus tissue, as told in our thymosin beta-4 story. It has 43 amino acids, is acetylated at the start, and is found inside nearly all cells, where it binds actin monomers and helps regulate the cell skeleton.
The short region
Studies mapping which part of the peptide binds actin pointed to a central stretch, with the one-letter sequence LKKTETQ at positions 17 to 23. Research on fragments of the molecule has used this region, often with an acetyl group on the first residue. That is a heptapeptide, seven residues, with a mass under 1,000 daltons, while the full molecule is about five times larger.
Why the label is ambiguous
TB-500 is a trade name, not a standardized chemical name like those used for official drugs. Different sources describe it as the full-length molecule, as a synthetic version of it, or as a fragment. A buyer who relies on the name alone cannot tell which one is in the vial.
How the report settles it
- Sequence: the report should name the sequence or at least the number of residues.
- Mass: about 4963 for full-length thymosin beta-4, under 1,000 for a seven-residue fragment. This is an instant check, as in MS/MS sequencing and HPLC versus mass spectrometry.
- Purity: a single dominant peak on HPLC, with the correct retention behavior.
- Lot number: tying the report to the actual vial, as in our report authenticity guide.
In a blend
In a two-peptide blend, the question applies to both components. The report should show each one separately. For how to read a blend, see our blend research post, and for the BPC-157 half see the BPC-157 sequence guide.
Related reading
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For laboratory research use only. Not for human or veterinary use, and not intended to diagnose, treat, cure or prevent any condition. This article is educational and is not medical advice.