TB-500 and thymosin beta-4 are routinely treated as the same thing. They are not. One is a 43-residue protein; the other is a short fragment taken from it. Which one is in a vial is a question the certificate answers and the product name does not.
What thymosin beta-4 is
A 43-residue protein found widely in cells, characterised as an actin-sequestering peptide: it binds monomeric actin and holds it in a pool that is not available for polymerisation. (Reference: Safer et al., 1991) That function was established by work identifying it with a previously described actin-sequestering factor, and related family members were shown to share the property. (Reference: Yu et al., 1993)
What TB-500 is
A seven-residue fragment, usually given as the acetylated sequence Ac-LKKTETQ, corresponding to a region of thymosin beta-4 associated with actin binding. Fragments of the protein have been studied separately from the whole molecule. (Reference: Rossdeutsch et al., 2007)
Seven residues against forty-three is not a small difference. Our molecular weight calculator returns C36H66N10O13 and about 847 g/mol for the free heptapeptide; acetylating the N-terminus adds C2H2O, giving roughly 889. The full protein is around 4,900. A mass measurement distinguishes them immediately, which is why a mass belongs on the certificate.
Why a fragment is sold at all
Short chains are cheaper to make and far easier to purify, which is the practical answer. A 43-residue protein made by stepwise synthesis would arrive carrying a long tail of deletion sequences; seven residues does not have that problem.
The scientific answer is that fragments of a protein are a standard way to ask which part of it carries a property. That is a legitimate line of work, and it is also why a fragment and its parent should never be described interchangeably: the whole point of making the fragment is that it might behave differently.
The naming problem is the verification problem
Our listing carries no CAS number for this compound, and that is the accurate position, not an omission to apologise for. A number is assigned when a substance is indexed in the chemical literature, and a fragment sold under a trade-style name may not have one of its own. Supplying a number that belongs to the parent protein would be worse than supplying none, because it would pass a check digit and resolve to the wrong molecule.
That failure mode is real and we have seen it in our own catalogue: another product here carried a CAS number that passed the arithmetic and resolved in PubChem to an unrelated lipid. The arithmetic never sees the compound name. Looking the number up is the step that catches it, and having no number at all is more honest than having one that misleads.
Reading the two names on a page
Catalogues use "TB-500", "thymosin beta-4" and "TB4" in ways that do not map onto a single molecule. A listing titled with one name and a certificate reporting the other is not necessarily dishonest; it is often a template filled in carelessly. Either way the vial contains one of them and the measured mass says which.
The general rule our note on CAS numbers sets out applies here with force: a compound can carry several names and names drift, while an identifier and a measured mass do not. When the names in a market are this loose, the measurement is doing all the work.
What a certificate has to state
Which molecule was analysed, explicitly: the fragment or the protein. Then the sequence, including whether the N-terminus is acetylated, because that modification changes the mass by forty-two daltons and is invisible in a letter sequence.
Purity from RP-HPLC with its conditions written out. Identity from mass spectrometry with observed and theoretical mass both shown, which is the measurement that settles fragment against protein.
Net peptide content separately from purity. This matters more on short peptides than on long ones: counterion and absorbed water are a larger share of the weighed powder when the peptide itself is light. Our note on what else is in the vial covers it.
Why high purity is unremarkable here
Seven residues means six coupling steps in synthesis. Each step is an opportunity for an incomplete reaction, so a heptapeptide starts from a far better position than a chain of forty. A figure of 99 percent on this compound represents much less work than the same figure on a long peptide, and purity percentages are not comparable across lengths.
On a short peptide the number worth reading is the identity measurement, not the purity percentage. A document that gives you 99 percent and no mass has given you the easy half of the answer.
Storage
A short peptide has fewer sites to degrade than a long one, which helps, and it is still hygroscopic once the vial is open. The usual routes proceed with time and temperature. (Reference: Manning et al., 2010) The threonine and glutamine residues in this sequence give deamidation somewhere to act, which is one reason the date on a certificate is worth reading. Our note on storage covers the chemistry.
What this page does not claim
The actin-sequestering property described in the literature belongs to the full protein. Whether a seven-residue fragment reproduces it is a separate question, and one a catalogue page is in no position to settle. What a seller can state is the sequence, the mass and the batch, which is where this page stops.
Research use only
All products sold by Codex Research are strictly for laboratory research and development. They are not for human or animal consumption and are not intended to diagnose, treat, cure, or prevent any disease.
The compound at Codex Research
TB-500, 10 mg per vial · batch-verified, with its certificate of analysis.
Frequently asked questions
Is TB-500 the same as thymosin beta-4?
No. Thymosin beta-4 is a 43-residue protein. TB-500 is a seven-residue fragment taken from it, usually the acetylated sequence Ac-LKKTETQ. Their masses differ by roughly a factor of five.
What is the mass of TB-500?
The free heptapeptide LKKTETQ is C36H66N10O13, about 847 g/mol. Acetylating the N-terminus adds C2H2O, giving roughly 889. The full protein is around 4,900.
Why does this product have no CAS number?
A number is assigned when a substance is indexed in the chemical literature, and a fragment sold under a trade-style name may not have one. Supplying the parent protein number would pass a check digit and resolve to the wrong molecule.
What must the certificate state that a name does not?
Which molecule was analysed, the sequence, and whether the N-terminus is acetylated. Acetylation changes the mass by forty-two daltons and is invisible in a letter sequence.
Is 99 percent purity impressive on TB-500?
Not particularly. Seven residues means six coupling steps, far fewer chances for incomplete reactions than a long chain. On short peptides the identity measurement is the number worth reading.
Does the fragment do what the protein does?
The actin-sequestering property described in the literature belongs to the full protein. Whether a seven-residue fragment reproduces it is a separate question that a catalogue page cannot settle.
References
- Safer, D., Elzinga, M., & Nachmias, V.T. (1991). Thymosin beta 4 and Fx, an actin-sequestering peptide, are indistinguishable. Journal of Biological Chemistry, 266(7), 4029-4032.
- Yu, F.X., Lin, S.C., Morrison-Bogorad, M., Atkinson, M.A., & Yin, H.L. (1993). Thymosin beta 10 and thymosin beta 4 are both actin monomer sequestering proteins. Journal of Biological Chemistry, 268(1), 502-509.
- Rossdeutsch, A., Smart, N., & Riley, P.R. (2007). Thymosin beta-4 and Ac-SDKP: tools to mend a broken heart. Journal of Molecular Medicine, 86(1), 29-35.
- Merrifield, R.B. (1963). Solid phase peptide synthesis. I. The synthesis of a tetrapeptide. Journal of the American Chemical Society, 85(14), 2149-2154.
- Manning, M.C., Chou, D.K., Murphy, B.M., Payne, R.W., & Katayama, D.S. (2010). Stability of protein pharmaceuticals: an update. Pharmaceutical Research, 27(4), 544-575.
- Dong, M.W. (2006). Modern HPLC for Practicing Scientists. Wiley.