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.
A plain-language reading of the TB-500 / thymosin beta-4 literature — what the cardiac, wound and repair studies actually measured, where the human evidence stops, and how compounded access really stands.
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.
Read the evidence, not the marketing
Every figure on this site is attributed to the study that produced it, with the species and the route stated. Where the human record is thin, the page says so rather than rounding up.