# TB-500: Research Overview — Pro Peptide Strip > A literature summary of TB-500 (Ac-LKKTETQ), the actin-binding fragment of thymosin beta-4: the fragment-versus-full-protein distinction, actin biology, human Phase 1 data and safety signals. Ac-LKKTETQ is the actin-binding motif of thymosin beta-4 — but most of the healing evidence in the literature belongs to the full 43-residue parent protein, not the seven-amino-acid fragment. ## The short version TB-500 is a small synthetic peptide — seven amino acids, sequence Ac-LKKTETQ — corresponding to the actin-binding region of a larger natural protein, thymosin beta-4 (Tβ4). Actin is part of the internal skeleton cells use to maintain their shape and to migrate toward a wound; by regulating actin dynamics, the parent protein is closely tied to cell movement, healing, and new blood-vessel growth [11]. The single most important distinction about TB-500: in the store and in anti-doping labs, "TB-500" refers to the seven-amino-acid fragment. But most published *efficacy* research was conducted with full-length thymosin beta-4, which is roughly five times larger [1]. It is not established that the small fragment reproduces what the whole protein does at the doses used in peptide research. TB-500 is not an approved medicine; it is banned in sport; and this page reports doses only as they were studied — never as advice. ## What it is TB-500 is a synthetic, N-terminally acetylated heptapeptide with sequence Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH, corresponding to residues 17-23 of thymosin beta-4 (Tβ4; gene TMSB4X), the endogenous 43-amino-acid G-actin-sequestering protein. This LKKTETQ stretch is the conserved actin-binding region of the beta-thymosin family. The identity distinction matters throughout this page: the fragment sold as "TB-500" weighs approximately 889 daltons; full-length Tβ4 is approximately 4,963 daltons. The X-ray crystallographic structure of the G-actin / Tβ4-derived gelsolin-hybrid complex established that Tβ4 forms a 1:1 complex with G-actin, capping both ends of the monomer and preventing polymerization — the structural basis for its actin-buffering role [16]. Where a study below used the full protein rather than the 7-mer, this page flags it. ## How it works Full-length thymosin beta-4 is the body's major intracellular G-actin sequestering peptide. "G-actin" is the free, single-unit form of actin; "sequestering" means Tβ4 binds and holds those units in an unpolymerized pool, available for rapid assembly when a cell needs to crawl, divide, or reshape. Crystal-structure work confirmed the 1:1 G-actin capping mechanism at 2-angstrom resolution [16]. By regulating the actin skeleton, Tβ4 (and the LKKTETQ motif it contains) is associated with faster cell migration, new blood-vessel growth, anti-inflammatory signaling, reduced apoptosis, decreased scar-forming myofibroblast activity, and recruitment of progenitor cells — a consolidated mechanism described across dermal-wound, corneal, heart and CNS models [11]. Whether the isolated seven-amino-acid TB-500 fragment reproduces all of that at the doses used in peptide research has not been shown in controlled human trials [1][11]. ## What the research shows *Regulatory and safety framing.* A 2026 Sports Medicine narrative review covering TB-500/thymosin beta-4 and BPC-157 among unapproved musculoskeletal peptides concluded that unapproved peptides show favorable tissue-repair outcomes in animal models but that rigorous human safety data are scarce, the potential for serious harm exists, and these compounds operate largely outside regulatory oversight [1]. *Consolidated mechanism.* A multi-model review consolidated thymosin beta-4's actin-binding, pro-migratory, anti-scarring, anti-inflammatory and angiogenic activities as the rationale for clinical development in dermal wounds, corneal injury, heart and CNS repair [11]. Note: this review addresses full-length Tβ4. *Structural basis.* X-ray crystallography of a gelsolin-domain-1-Tβ4 hybrid bound to actin established that Tβ4 forms a 1:1 complex with G-actin, sequesters the monomer by capping both ends, and prevents polymerization; the WH2 actin-interacting motif underlies this [16]. *Human safety (full-length protein, not the fragment).* In a randomized, placebo-controlled Phase 1 study, synthetic thymosin beta-4 was given intravenously to 40 healthy volunteers — single dose then daily for 14 days at 42, 140, 420 or 1260 mg. Well tolerated; only infrequent mild-to-moderate adverse events; no dose-limiting toxicities; no serious adverse events; dose-proportional pharmacokinetics [15]. This data is for full-length Tβ4, not the TB-500 fragment. *Animal dose-response (full-length protein).* In male Wistar rats with embolic middle cerebral artery occlusion, intraperitoneal thymosin beta-4 at 2 and 12 mg/kg (starting 24 h post-stroke, then every 3 days for 4 more doses) improved neurological function significantly from day 14 through day 56; 18 mg/kg gave no significant benefit — a non-monotonic result where more was not better [14]. ## Reported effects, cautions & safety No community-anecdote signals are compiled in this desk's source material for TB-500 as a standalone. The following cautions come from the cited literature. - *Identity confusion.* Most efficacy claims for TB-500 rest on full-length thymosin beta-4 data. It is not established that the Ac-LKKTETQ fragment reproduces the parent protein's effects; efficacy claims for the fragment in humans are unproven [1]. - *Tumor / angiogenesis signal.* Thymosin beta-4 is overexpressed in several cancers (e.g., pancreatic, colorectal) and implicated in metastasis and tumor angiogenesis. The same pro-migratory, pro-angiogenic properties that aid repair could theoretically support tumor progression [11]. - *Non-monotonic dosing.* In the rat stroke dose-response study, 2 and 12 mg/kg improved outcomes but 18 mg/kg did not — higher is not necessarily better, undermining community loading rationales [14]. - *No human trials for the fragment.* No completed controlled clinical trials of the TB-500 heptapeptide fragment exist for any indication [1]. - *WADA prohibition.* TB-500 (and thymosin beta-4) are prohibited by WADA under peptide/growth-factor categories; banned in and out of competition. TB-500 has been detected as a doping agent in racehorses, prompting dedicated LC-MS anti-doping assays [1]. - *Unregulated supply.* TB-500 is not an approved drug; product identity, purity and correct sequence (full-length vs fragment) are not guaranteed in unregulated supply. ## Where it fits in recovery research TB-500 occupies a particular position on this desk: a compound whose *mechanism* — actin regulation driving cell migration — is well described at the full-protein level, but whose *evidence as the actual sold fragment* is the thinnest of the four [1]. It is a component of both [Wolverine](/wolverine) and [KLOW](/klow). Where [BPC-157](/bpc-157) leads with angiogenesis, TB-500's story is largely thymosin beta-4's story, borrowed — making it the clearest case study in why this field rewards reading the primary citations rather than the marketing. See the [comparison page](/compare) for how all four line up. ![TB-500 actin-binding fragment and cytoskeletal dynamics illustration](/images/tb-500.webp) --- A clinical literature briefing on research peptides — peer-reviewed citations, no products, no prescriptions.