Naming clarification
TB-500 vs thymosin β-4: fragment vs parent protein
Thymosin β-4 (Tβ4) is a naturally occurring 43-amino-acid, N-acetylated protein of about 4.9 kDa (gene TMSB4X, UniProt P62328). TB-500 is a shorter synthetic peptide fragment drawn from the actin-binding region of that protein, commonly supplied as Ac-LKKTETQ (residues 17–23). The two names refer to chemically different molecules; this page sets the vocabulary and cites the public database entries. Research use only.
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At-a-glance comparison
| Field | Thymosin β-4 (Tβ4) | TB-500 (synthetic fragment) |
|---|---|---|
| Chemical identity | 43-residue, N-acetylated protein | Short synthetic peptide fragment (vendor-dependent) |
| Common sequence | Ac-SDKPDMAEIEKFDKSKLKKTETQEKNPLPSKETIEQEKQAGES | Ac-LKKTETQ (residues 17–23); some vendors use other fragments |
| Length | 43 amino acids | Typically 7 amino acids (fragment length varies) |
| Approximate mass | ≈ 4.9 kDa | ≈ 889 g/mol for Ac-LKKTETQ |
| Origin | Naturally occurring intracellular protein | Synthetic, from solid-phase peptide synthesis |
| Reference database | UniProt P62328 | Vendor COA (identifier varies by fragment) |
| Dedicated page | Thymosin β-4 reference | TB-500 reference |
Thymosin β-4 (parent protein)
Thymosin β-4 is a member of the β-thymosin family of small intracellular actin-sequestering proteins. The reference entry on UniProt is P62328; the gene is TMSB4X on the X chromosome (NCBI Gene 7114). The mature protein is N-terminally acetylated, 43 residues long, and about 4.9 kDa. Full-length thymosin β-4 is studied as a protein in its own right in the published literature, independent of its shorter fragments.
TB-500 (synthetic fragment)
TB-500 is the research-chemical name applied to a synthetic peptide fragment taken from the actin-binding motif of thymosin β-4. The most common vendor form is Ac-LKKTETQ — the N-acetylated form of residues 17–23 — but the exact fragment definition varies by vendor. The mass on the vial should match the fragment on the vendor COA.
Why the names get mixed up
Vendor and community usage uses “TB-500” and “thymosin β-4” as if they were the same material. They are not: a fragment of a molecule is a different molecule than the full version, with a different mass, a different synthesis route and a different COA signature. For a careful read of the published literature it is worth noting which one a given paper studied.
How each is identified in the lab
Both molecules are identified by mass spectrometry (observed mass vs. computed mass of the stated sequence) and quantified or purity-reported by HPLC. The purity testing methods explainer walks through the techniques; the how to read a peptide COA guide covers how a specific lot report is laid out.
Related pages: TB-500 reference, Thymosin β-4 reference, BPC-157 vs TB-500, BPC-157 and TB-500 combined blend.
Frequently asked questions
Is TB-500 the same as thymosin β-4?
No. Thymosin β-4 (Tβ4) is a naturally occurring 43-amino-acid, N-acetylated protein of about 4.9 kDa, encoded by the gene TMSB4X and catalogued as UniProt P62328. TB-500 is a shorter synthetic peptide fragment based on its actin-binding region, commonly supplied as Ac-LKKTETQ (residues 17–23).
Why are the two names used interchangeably?
Vendor and community usage. "TB-500" is the research-chemical name applied to the synthetic actin-binding fragment, and because that fragment is drawn from thymosin β-4 the full protein is often invoked as shorthand. The names refer to chemically different molecules — a fragment versus the full protein.
What is the actin-binding region of thymosin β-4?
The seven-residue motif LKKTETQ, corresponding to residues 17–23 of the mature thymosin β-4 sequence. This motif is the basis of the TB-500 synthetic fragment used in laboratory research.
How different are their molecular masses?
The full thymosin β-4 protein is approximately 4.9 kDa (43 residues, N-terminally acetylated). The common TB-500 fragment Ac-LKKTETQ is about 889 g/mol (7 residues plus the acetyl group) — a difference of roughly 5.5-fold. Verify the exact fragment mass on the supplier COA for whichever product is sourced.
Which one is in the Wolverine Blend research vial?
The Wolverine Blend vial contains the synthetic fragment commonly labelled TB-500 (paired with BPC-157) — not the full 43-residue thymosin β-4 protein. Verify the exact fragment identifier on the per-lot COA.