# TB-500: The Synthetic Ac-LKKTETQ Peptide and What the Research Record Shows > TB-500 is the synthetic Ac-LKKTETQ heptapeptide carrying thymosin beta-4's actin-binding motif. A cited digest that keeps the fragment's evidence separate from the full-length protein's. Two signals overlap on this page and they are not the same trace: the seven-residue fragment sold as TB-500, and the forty-three-residue protein whose data the marketing borrows. We log which molecule each finding belongs to, and cite every number. ## TB-500 in one readout TB-500 is a synthetic, N-acetylated heptapeptide with the sequence Ac-LKKTETQ — seven amino acids that correspond to residues 17-23 of thymosin beta-4, the conserved actin-binding region of the protein. Molecular weight is 889.02 Da; the molecular formula is C38H68N10O14. It is supplied as a lyophilized powder for laboratory and veterinary research, and it has no approved human therapeutic indication. One fact sits above all the others here, and it is a signal-integrity problem. "TB-500" in commerce and in anti-doping science is the ~889 Da fragment. Most of the published *efficacy* research, though, was run on full-length thymosin beta-4 — a ~4963 Da protein the parent of that fragment [5]. The 7-mer and the 43-mer are two overlapping channels, and it is not established that the fragment reproduces the parent protein's effects at the doses used in peptide research [5]. This digest keeps the two channels visibly separate so a reader can always see which molecule a given result came from. The parent protein is worth a sentence on its own. Thymosin beta-4 is the body's principal G-actin sequestering peptide, present in nearly all human cells and released by platelets and macrophages at sites of injury [13]. The LKKTETQ segment inside TB-500 is the part of that protein that grips actin. What TB-500 does *not* carry is the protein's N-terminal end, which means it cannot generate Ac-SDKP, a separate anti-fibrotic cleavage product of the full-length molecule. That distinction matters whenever a "TB-500" claim is actually built on whole-protein data. ## TB-500: The Synthetic Ac-LKKTETQ Peptide As a research chemical, the TB-500 peptide is defined by its sequence rather than by any approved use. Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln is short, acetylated at the N-terminus, and chemically more robust than the full-length protein — though still subject to proteolysis and freeze-thaw degradation. There is no single PubChem CID or CAS number consistently registered for the fragment under the name TB-500; identifiers in the literature usually point to the parent protein (gene TMSB4X, UniProt P62328). The "chemical" framing is the honest one for this compound, because TB-500's real-world fame is analytical. It surfaced as a designer peptide in equine sport, which prompted the first liquid-chromatography mass-spectrometry methods to detect the parent peptide and its metabolites in horse plasma and urine. In other words, the TB-500 peptide is best characterized today not by a finished-drug file but by detection assays and a structural definition — a captured signal, not a clinical product. Research-grade material quality is its own recurring caveat. Peptide identity, purity, and correct sequence — full-length versus fragment — are not guaranteed in unregulated supply, which also complicates the interpretation of any anecdotal result. The studies summarized across this site used characterized material; community-sourced material may not match it. ## TB-500 vs Full-Length Thymosin Beta-4 thymosin beta-4 is the 43-amino-acid protein from which TB-500 is carved, and most of the data attached to the TB-500 name actually describe this larger molecule. Reviews of thymosin beta-4 credit it with binding actin, mobilizing cells, reducing myofibroblast number to limit scar formation, dampening inflammation, and promoting angiogenesis — the basis on which clinical trials in dermal wounds, corneal injury, and heart and CNS repair were launched [5]. The single most important human dataset belongs to the full-length protein, not the fragment. In a randomized, placebo-controlled Phase 1 study, synthetic thymosin beta-4 given intravenously to 40 healthy volunteers — single dose then daily for 14 days at 42, 140, 420, or 1260 mg — was well tolerated, with only infrequent mild-to-moderate adverse events, no dose-limiting toxicities, and no serious adverse events; pharmacokinetics were dose-proportional [6]. That is reassuring data about thymosin beta-4. It is not data about Ac-LKKTETQ. The practical takeaway: read every "TB-500" benefit claim and ask which molecule produced it. On this site, findings that come from the fragment are marked as fragment findings; findings that come from full-length thymosin beta-4 are marked as such. See [the actin-sequestration mechanism](/research) for how the shared LKKTETQ motif works, and [TB-500 vs full-length thymosin beta-4](/research) for the full comparison. ## What this digest covers This is an editorial reading of the published record, organized so the strongest established findings and the honest gaps are both easy to find. The mechanism — 1:1 G-actin sequestration via the WH2-type LKKTETQ motif — is laid out on the research page [1]. The wound-healing, cardiac, neurological, and anti-inflammatory studies, almost all conducted with full-length thymosin beta-4, are summarized there too, each tagged to its species and dose. The [human clinical data on thymosin beta-4](/research) — a Phase 1 intravenous safety study — is set out alongside them, clearly marked as protein data rather than fragment data [6]. The dealt focus of this particular digest is hair. Thymosin beta-4 at nanomolar concentrations stimulated hair growth in normal rats and mice by activating hair-follicle bulge stem cells [7], and the [TB-500 hair growth research](/hair-research) page collects that literature in one place. A second focus is access: the [TB-500 legal status and 503A category](/legal-status) page states the present-tense FDA and anti-doping standing from a single audited reference. Where the data thin out, this digest says so plainly. There are no completed controlled clinical trials of the TB-500 heptapeptide for any indication [5]. The full [doses used in the research literature](/dosage) are animal and full-protein doses, framed as such, never as a human protocol. The same pro-angiogenic activity that aids repair is also the unresolved tumor-progression concern flagged in the [TB-500 side effects and safety signals](/faq). Every quantitative claim on this site resolves to the [full reference list](/references). --- A chromatic-split scope reading of the TB-500 record — the Ac-LKKTETQ fragment held on one channel and full-length thymosin beta-4 on the other so the two are never mistaken for one trace, the FDA 503A standing read before anything else, with no clinic behind the scope and nothing here dispensed or sold.