Research digest · Thymosin beta-4 fragment
TB-500 is the actin-binding fragment of thymosin beta-4, read here across the cardiac and repair literature.
Most of the efficacy data sit on the full-length parent protein, not the seven-residue fragment. This site keeps the two apart, cites every measured number, and marks where the human evidence stops.
What TB-500 actually is
TB-500 is a synthetic, N-acetylated heptapeptide with the sequence Ac-LKKTETQ — seven amino acids corresponding to residues 17–23 of thymosin beta-4, the conserved actin-binding region of the body's principal G-actin-sequestering peptide [5]. That seven-residue motif is the whole of TB-500. It is not an endogenous molecule; it is a fragment manufactured to carry the parent protein's actin-binding core.
The parent protein, thymosin beta-4 (Tβ4, gene TMSB4X), is a 43-amino-acid peptide of roughly 4963 Da present in nearly all human cells and released by platelets and macrophages at sites of injury [5]. TB-500 itself is about 889 Da. The size gap matters, and it is the single most important thing to understand before reading any claim about this compound: the overwhelming majority of published efficacy research was conducted with full-length Tβ4, not the heptapeptide marketed as TB-500. Where a finding used the full protein, this site says so.
TB-500 has no FDA-approved therapeutic indication and is prohibited in sport by the World Anti-Doping Agency. It is sold by research suppliers for laboratory use and circulates in veterinary contexts. The studied biology is real and, in places, precisely measured; the human evidence for the fragment specifically is not. Both statements are true at once, and the pages here hold them together rather than choosing one.
TB-500 Peptide: The Ac-LKKTETQ Fragment of Thymosin Beta-4
The TB-500 peptide is the Ac-LKKTETQ sequence and nothing more — a single acetylated heptapeptide, molecular formula C38H68N10O14, molecular weight approximately 889.02 Da. LKKTETQ is the actin-binding motif of the beta-thymosins, the short stretch through which thymosin beta-4 grips a monomer of actin [1].
In commerce and in the anti-doping literature, "TB-500" denotes this fragment. In the efficacy literature, the same name is routinely attached to data generated with the full ~4963 Da protein. That conflation is not a pedantic distinction — it is the central honesty problem of the category. Whether the isolated seven-mer reproduces the full protein's effects at the doses used in peptide research has not been established in controlled human trials [5]. A short acetylated peptide is chemically more robust than the full-length protein but still subject to proteolysis, and the identity and purity of research-grade material are a recurring concern.
The practical reading: when a sentence on this site reports a cardiac, wound, or stroke result, check whether it names Tβ4 or the fragment. That single habit separates what is measured from what is marketed.
Thymosin Beta-4: The Parent Protein Behind TB-500
Thymosin beta-4 is a ubiquitous 43-residue peptide and the body's main intracellular G-actin sequestering molecule. It binds a single monomer of globular (G-) actin 1:1 and caps both ends of that monomer, holding a buffered reserve of unpolymerized actin and regulating how the cytoskeleton assembles and how cells migrate [1]. The 2 Å crystal structure of a gelsolin-domain-1–Tβ4 hybrid bound to actin established that 1:1 sequestration mechanism directly [1].
Because the body releases Tβ4 from platelets and macrophages after injury, it sits at the intersection of several repair processes: cell migration, angiogenesis, anti-inflammatory and anti-apoptotic signaling, and reduced scar formation [5]. Those properties are why Tβ4 reached human trials in dermal wounds, corneal injury, and cardiac and CNS repair — and why a heptapeptide carved from its actin-binding region attracts repair interest.
It also carries the caveat forward. Tβ4 generates Ac-SDKP, an N-terminal cleavage product with its own anti-fibrotic and angiogenic activity — and that product comes from a different region of the protein than TB-500, so the fragment does not produce it [5]. Reading the parent protein's record as if it were the fragment's record overstates what the seven-mer has been shown to do.
The deeper reads live on the mechanism of action page; the regulatory standing is set out under TB-500 legal status.
What is TB-500?
TB-500 is a synthetic, N-acetylated heptapeptide (Ac-LKKTETQ) corresponding to residues 17–23 of thymosin beta-4, the actin-binding motif of the body's main G-actin-sequestering peptide [5]. It is sold for research and veterinary use and is not approved for humans.
What does TB-500 stand for?
TB refers to thymosin beta-4, the parent protein. TB-500 is a research and veterinary designation for the synthetic Ac-LKKTETQ fragment of that protein — a market name, not an official chemical name [5].
What is TB-500 used for in research?
Thymosin beta-4 and its actin-binding region have been studied in animal and topical-human models for wound and corneal healing, cardiac and neurological repair, angiogenesis, and anti-fibrotic effects [5][3]. Human efficacy of the seven-mer specifically is unproven.