TB-500 vs thymosin β4: what a COA must confirm

The short answer

TB-500 is the acetylated 17–23 fragment of thymosin β4 — a seven-residue peptide of roughly 889 Da, not the full 43-residue 4,963 Da protein. Because the two are routinely conflated in marketing, the mass reported on a certificate of analysis is the fastest way to confirm which molecule you actually have.

The fragment is not the protein

Thymosin β4 is a 43-amino-acid protein of about 4,963 Da. TB-500, as supplied for research, is an N-terminally acetylated seven-residue fragment corresponding to residues 17–23 of that protein — the region associated with actin binding — with a mass near 889 Da.

That is a difference of more than four thousand daltons between two things frequently sold and discussed under overlapping names. It is not a subtle distinction, and any intact-mass measurement resolves it immediately. If a certificate reports a mass around 4,963 Da, the vial does not contain the fragment; if it reports around 889 Da, it does.

Published characterisation of the fragment exists precisely because the material was circulating and needed identifying — analytical chemists sequenced what was actually in the products rather than what the labels claimed. That literature is the reason the expected mass is known with confidence.

A second, subtler substitution

Beyond the fragment-versus-protein confusion sits a closer one. The same seven-residue sequence without the N-terminal acetyl group is a distinct compound, and it differs from TB-500 by exactly 42 Da — the mass of the acetyl group itself.

Forty-two daltons is a small gap relative to the molecule, but it is entirely resolvable by mass spectrometry at ordinary resolution. What it requires is that identity be tested at all, rather than inferred from a purity percentage. A certificate reporting 99% purity without an identity determination cannot distinguish between these two.

This is the general lesson in a specific case: purity tells you how much of the peptide content is a single species. Identity tells you which species it is. Only the pair together describes the vial.

What to check on a TB-500 certificate

Confirm the reported mass sits near 889 Da, consistent with the acetylated heptapeptide rather than the full protein or the non-acetylated form. Confirm identity was determined by mass spectrometry or comparison against a reference standard, and that the method is stated rather than implied.

Then apply the ordinary checks: the lot number matches the vial, purity is reported against a stated specification and method, and contamination controls — elemental impurities, endotoxin, sterility — are present rather than absent. USP General Chapter ⟨1503⟩ sets out the attributes expected of synthetic peptide substances and is a useful yardstick for what a complete panel covers.

Finally, verify the document with the laboratory that issued it. For a compound with this much naming ambiguity, an unverifiable certificate is particularly weak evidence — the name on the page is exactly the thing in question.

It is worth understanding why the confusion persists rather than treating it as carelessness. The fragment and the parent protein are genuinely related: the fragment corresponds to the actin-binding region of thymosin β4, so describing it in terms of the parent is not entirely wrong. What is wrong is treating the two as interchangeable when they differ by a factor of five in mass and were characterised separately in the analytical literature. The synthesis economics differ enormously as well — a seven-residue peptide and a 43-residue protein are not comparable manufacturing problems — which is part of why the shorter fragment is what actually circulates under the name.

Questions researchers ask

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

No. TB-500 as supplied is an acetylated seven-residue fragment (residues 17–23) of about 889 Da, while full thymosin β4 is a 43-residue protein of about 4,963 Da. They are frequently discussed interchangeably in marketing, but they are different molecules and a mass measurement separates them immediately.

What molecular weight should TB-500 show on a COA?

Approximately 889 Da for the N-terminally acetylated 17–23 fragment. A result near 4,963 Da indicates full-length thymosin β4 instead, and a result near 847 Da indicates the non-acetylated heptapeptide — 42 Da lighter, the mass of the missing acetyl group.

How do I tell if TB-500 is actually the acetylated fragment?

By intact-mass measurement reported on a lot-specific certificate. The acetyl group contributes 42 Da, so the acetylated and non-acetylated forms are readily distinguished by mass spectrometry. Purity percentage alone cannot make this call, because both forms could be individually pure.

Does TB-500 have approved human use?

No. There is no approved human therapeutic use of the TB-500 fragment. Human clinical work in this area has generally used full-length thymosin β4 rather than the fragment. Material sold as TB-500 is supplied for laboratory research only.

At a glance

Class: Synthetic acetylated heptapeptide (7 residues), thymosin β4 fragment 17–23
Expected mass: ≈ 889 Da (full thymosin β4 is ≈ 4,963 Da)
Common mislabel: Full-length thymosin β4; non-acetylated heptapeptide (≈ 42 Da lighter)
Form: Lyophilised powder
Status: Research use only — no approved human use of the fragment

How our TB-500 lots test

Applying the same standard described above to our own material. Each certificate below opens on the issuing laboratory's portal— not a PDF hosted here — so you are reading the lab's record, not ours.

10mg · Lot WY703014 · 99.73% pureView verified COA ↗

Sources

Written from primary literature and published standards — never from other suppliers' marketing copy.

Written by Ivory Science. Scientific review: pending appointment of a named reviewer. Until then this page cites its sources directly so every claim can be checked at origin.

TB-500 in the catalogue All research notes How to judge a supplier

For research use only. Not for human or veterinary use, ingestion or administration. Nothing here is medical advice, and no statement on this page has been evaluated by the FDA. TB-500 is not an approved medicine.

TB-500 vs thymosin β4: reading the certificate of analysis