Thymosin β4 (full length)
- Length
- 43 amino acids
- Sequence
- SDKPDMAEIEKFDKSKLKKTETQ…
- Molecular weight
- ≈ 4963 Da
- CAS number
- 77591-33-4
- Relationship
- Parent molecule
Research library TB-500 and Thymosin β4
Literature review
TB-500 and Thymosin β4: Two Different Molecules, One Label
Article
Last reviewed: August 2026 · Literature review · No dosage or administration information.
01 / Overview
Two different molecules, one label
The label "TB-500" is used in the research materials market for at least two chemically distinct substances. They differ in length, in molecular weight by roughly a factor of five, and in what the published literature actually describes. A buyer comparing prices across suppliers is frequently comparing two different molecules without knowing it. This article sets out what each one is and how to tell them apart from the specification sheet alone.
Thymosin β4 is a 43-amino-acid peptide, N-terminally acetylated, with a molecular weight of approximately 4963 Da. It occurs naturally and is the subject of most of the published work that the term "TB-500" is used to invoke. Its actin-binding region is a short sequence at positions 17 to 23: LKKTETQ. That seven-residue fragment, acetylated at the N-terminus, is itself sold as "TB-500". Its molecular weight is approximately 889 Da. It is a fragment of the parent molecule, not the parent molecule.
02 / Comparison
Full length and fragment
TB-500 (heptapeptide fragment)
- Length
- 7 amino acids
- Sequence
- Ac-LKKTETQ
- Molecular weight
- ≈ 889 Da
- CAS number
- 885340-08-9
- Relationship
- Positions 17–23 of the parent
03 / Reading the specification
The sequence resolves the label
The practical consequence is that a specification sheet reading "TB-500 (Thymosin β4 Acetate)" is internally contradictory. It names the fragment and then defines it as the parent. Sheets of this kind are common, and they are not always deliberate — the naming confusion is inherited across the supply chain rather than invented at any one point in it.
Two figures resolve it without ambiguity. The first is molecular weight: 889 and 4963 are not close, and no analytical method returns both. The second is the sequence itself. A supplier who can state the sequence and produce a mass spectrometry result consistent with it has answered the question; a supplier who can produce neither has not.
Related products & records
Read the specification and the record
FLASK publishes the sequence, molecular formula, molecular weight and CAS number for every compound it lists, and files mass spectrometry results in the batch ledger. Where a name is ambiguous in the market, the specification is not.
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