CASE FILE No. 17-23 // SUBJECT: Ac-LKKTETQ
TB-500 is the heptapeptide fragment of thymosin beta-4 — and most of its evidence belongs to a different molecule.
A case review of the published record: what the studies measured, which findings are on the 7-mer versus the full-length parent protein, and where the human trail goes cold. Every quantitative claim is cited.
The case in one line
TB-500 is the synthetic, N-acetylated heptapeptide Ac-LKKTETQ — residues 17 to 23 of thymosin beta-4, the protein's actin-binding core [1]. That is the molecule sold and named TB-500, and the molecule characterized in anti-doping science. It is not the molecule behind most of the headline findings.
The overwhelming majority of the efficacy research credited to TB-500 was run on full-length thymosin beta-4 — the 43-residue, ~4963 Da parent protein — not on the ~889 Da fragment. This site reads the literature as a case file: each study is an exhibit, each finding carries a tag naming which molecule it is actually on, and the gaps are marked as gaps. The fragment has no completed controlled human trial for any indication.
What is TB-500?
TB-500 is the synthetic Ac-LKKTETQ heptapeptide carrying the actin-binding motif of thymosin beta-4 (Tβ4), the body's principal G-actin-sequestering peptide [1][5]. Its sequence is Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln, molecular weight ~889 Da, formula C38H68N10O14.
The parent protein is released by platelets and macrophages at sites of injury, where it is associated with cell migration, angiogenesis, and reduced scarring [5]. "TB-500" itself is a synthetic construct and a veterinary/commercial designation, not an endogenous species. The defining caveat of this whole file: whether the isolated 7-mer reproduces the parent protein's effects at the doses used in peptide research has not been established in controlled human trials.
TB-500 peptide: structure and identity
The TB-500 peptide is the acetylated heptapeptide form of the thymosin beta-4 actin-binding region. Acetylation of the N-terminus makes it more chemically robust than the full-length protein, though it remains subject to proteolysis and freeze-thaw degradation.
No single PubChem CID or CAS number is consistently registered for the Ac-LKKTETQ fragment under the name TB-500; published identifiers (TMSB4X, UniProt P62328) belong to the parent protein. In commerce and in the analytical literature, "TB-500" denotes the 7-mer; in most efficacy papers, the active agent is the full-length protein. That split is the source of nearly every overstated benefit claim, and it is the throughline of this review. The full reconstruction lives in the TB-500 mechanism of action file.
What this file establishes, and what it does not
On the record: thymosin beta-4 forms a 1:1 complex with monomeric actin and sequesters it by capping both ends, a structure resolved by X-ray crystallography to 2 Å [1]. In a rat full-thickness wound model, the parent protein raised re-epithelialization by 42% at 4 days and up to 61% at 7 days versus saline [3]. In healthy volunteers, intravenous full-length Tβ4 was well tolerated up to 1260 mg in a randomized, placebo-controlled Phase 1 study [6].
Unproven: the fragment's efficacy in humans. There are no completed controlled clinical trials of the TB-500 heptapeptide for any indication. The pro-angiogenic, pro-migratory properties that aid repair are also the basis of a tumor-angiogenesis safety concern, and thymosin beta-4 is overexpressed in several cancers [5]. Start with TB-500 tissue repair and wound healing, then weigh the safety signals in the TB-500 safety signals and side effects file.
How to read this case file
Each page of this site is an exhibit, and each exhibit is read with the same discipline: state what was measured, name the molecule it was measured on, and cite it. The research file reconstructs the mechanism and the studies — the 1:1 actin-sequestration structure [1], the cardiac PINCH–ILK–Akt result [2], the non-monotonic stroke dose-response [4], the null mdx-mouse strength outcome, and the safety signals. The tissue-repair file gathers the strongest exhibits, the wound and epithelial findings on the parent protein [3]. The dosage file logs what was administered, to which species, by which route — never a human protocol. The legal-status file sets out the regulatory facts.
What keeps the file honest is a single tag carried through every finding. A result on full-length thymosin beta-4 is marked as such; a result on the Ac-LKKTETQ fragment is marked as such; a claim that quietly swaps one for the other is flagged. Most marketing for TB-500 leans on parent-protein data without that tag, which is how a 7-mer with no completed human trial comes to be described as if the protein's decades of evidence were its own.
Why the mistaken-identity problem matters
The two molecules are not interchangeable on the evidence. Full-length thymosin beta-4 is a 43-residue protein with a documented mechanism, animal efficacy across several organ systems, and a human Phase 1 safety record [5][6]. TB-500 is a 7-residue fragment of it, sold and named for the parent, but tested directly in almost none of those settings.
That gap is not a technicality. It means the confident percentages a reader meets online — the re-epithelialization figures, the cardiac and neurological results — are real numbers attached to a different, larger molecule [3][4]. Whether the fragment reproduces them at the doses used in peptide research is exactly the question the literature has not answered. Reading the thymosin beta-4, the parent protein file first is the fastest way to see which claims are borrowed and which are earned.