TB-500 in Canada: Thymosin Beta-4 vs the Ac-LKKTETQ Fragment
Order TB-500 in Canada from three different suppliers and you may receive three different molecules. The name is attached most often to a short fragment of thymosin beta-4, sometimes to fragments of other lengths and, by a few sellers, to the full-length protein. The protein and the common seven-residue fragment differ in mass by a factor of more than five. This article sets out what each molecule is, how the confusion arose, and how a receiving or QC team can tell which one is in the vial before it goes into a study.
Thymosin beta-4: the parent protein
Thymosin beta-4 (Tβ4) is a small, highly conserved protein of 43 amino acids, acetylated at its N-terminal serine. Its molecular formula is C212H350N56O78S and its molecular weight is about 4963 g/mol. It is one of the most abundant intracellular peptides in many cell types and was first isolated from thymus tissue, which gave the thymosin family its name.
Its best-characterised job is structural. Tβ4 binds monomeric actin (G-actin) in a 1:1 complex and keeps it from polymerising into filaments, so it acts as a buffer that holds a pool of actin ready for rapid use. Much of the research interest in Tβ4, including in-vitro work on cell migration and in-vitro angiogenesis assays, follows from that actin-sequestering role.
Two short motifs inside the chain get most of the attention:
- Ac-SDKP (residues 1–4): the acetylated N-terminal tetrapeptide, released from Tβ4 by prolyl oligopeptidase and studied as a separate molecule in its own right.
- LKKTETQ (residues 17–23): the central actin-binding motif, the stretch most directly responsible for the interaction with G-actin.
Where the TB-500 name comes from
“TB-500” is a trade label rather than a chemical name, and no single sequence owns it. In the research-chemical market it most often refers to a short synthetic peptide built around the actin-binding motif, commonly the acetylated heptapeptide Ac-LKKTETQ (positions 17–23 with an acetyl cap on the N-terminus), although fragments of other lengths, with or without acetylation, are sold under the same name. Some sellers have also applied it to full-length synthetic Tβ4. Listings that call the fragment the “active region” of Tβ4 are stating a hypothesis drawn from actin-binding studies, not an established equivalence.
The practical result is that “TB-500” on a label tells you very little. It could mean the acetylated heptapeptide, a fragment of different length, or occasionally the full 43-residue sequence, and a listing that states only the trade name and a milligram amount has not told you which you are buying.
TB-500 fragment vs full-length Tβ4, side by side
| Property | Thymosin beta-4 (full length) | Ac-LKKTETQ fragment |
|---|---|---|
| Length | 43 residues | 7 residues |
| N-terminus | Acetyl-Ser | Acetyl-Leu |
| Approximate molecular weight | 4963 g/mol | 889 g/mol |
| Methionine present | Yes (position 6) | No |
| Contains Ac-SDKP motif | Yes | No |
| Contains actin-binding motif | Yes, in its native context | Yes, in isolation |
| Synthetic difficulty | High; long chain with more room for deletion impurities | Low; short and straightforward |
The table also explains why the two can behave differently in an assay. Tβ4 has no stable fold of its own and becomes helical only when it binds actin, so the residues flanking the motif help decide how well it is presented. A seven-residue peptide carries the recognition sequence without that context, and results from one molecule should not be assumed to transfer to the other. Literature on Tβ4 is literature on Tβ4.
Confirming what you received
Because the masses are so far apart, identity is easy to settle with mass spectrometry. A certificate or in-house spectrum showing a main species near 4963 Da indicates full-length Tβ4. A main species near 889 Da indicates the heptapeptide. Anything else calls for a conversation with the supplier.
A few secondary checks are useful for a QC lab handling the full-length protein:
- Methionine oxidation: Met6 can oxidise to the sulfoxide, which appears as a +16 Da companion to the main mass. A small amount is common; a growing amount across a stored lot points to exposure to air, light or warmth.
- Deletion sequences: in a 43-residue synthesis, peptides missing one residue are the typical process impurities. They elute close to the main peak on reversed-phase HPLC, so ask for the chromatogram, not just a purity figure.
- Acetylation: the N-terminal acetyl group adds 42 Da. A species 42 Da light suggests incomplete capping.
For the short fragment, the chromatography is simpler, but the same rule applies: purity is only meaningful once identity has been confirmed.
Ordering TB-500 in Canada for a volume study
For labs buying across many vials, the naming problem is best solved on paper before the order is placed. Write the specification in chemical terms rather than trade terms:
- State the sequence you require, including the N-terminal acetyl group.
- State the expected molecular weight, so a mismatch is obvious at receiving.
- Specify a minimum HPLC purity and request the chromatogram.
- Ask for a single batch across the order where possible.
- Record the batch identifier (a printed lot where one exists, otherwise cap and crimp colour) and the certificate reference against each group of vials when they arrive.
That short list also protects reorders. When the next purchase is checked against the same written specification, a silent change in what the supplier ships under the same name gets caught at the door rather than in your results.
Blends that include TB-500
TB-500 is often supplied in a single vial with BPC-157. The two are chemically unrelated, so a competent HPLC method separates them into two distinct peaks, and each should have its own identity confirmation by MS and its own purity figure. A blend report with a single number has not told you how pure either component is.
Bulk Peptides lists TB-500 as a single compound and in a TB-500 and BPC-157 blend. Our products are third-party tested for purity by HPLC, certificates are published for some products, and every vial is matched to its certificate by cap and crimp colour. Our vial pricing is mix-and-match, so every vial in the cart counts toward the volume break, and orders ship from within Canada. If you need to confirm which molecule a listing refers to before ordering, contact us and ask.
Thymosin beta-4, TB-500 and related materials are supplied by Bulk Peptides for in-vitro research only. They are not intended for human or animal use, and this article is not guidance on any such use.
