RESEARCH DIGEST · THYMOSIN BETA-4 FRAGMENT
TB-500 is the Ac-LKKTETQ thymosin beta-4 fragment, studied for hair, repair and tissue migration.
A luminous digest of what the published literature actually measured — follicle-stem-cell activation, re-epithelialization, the actin-sequestration mechanism — and an honest line on where the human evidence stops.
What the TB-500 literature describes
TB-500 is the synthetic, N-acetylated heptapeptide Ac-LKKTETQ — seven amino acids (Leu-Lys-Lys-Thr-Glu-Thr-Gln) that correspond to residues 17–23 of thymosin beta-4, the conserved actin-binding motif of the parent protein [6]. Molecular weight is roughly 889 Da; the molecular formula is C38H68N10O14. The fragment is small and synthetic. Its parent, thymosin beta-4, is a 43-residue protein present in nearly every human cell and released by platelets and macrophages at sites of injury [7].
One distinction governs everything on this site, so it leads here. Most published efficacy research was run with full-length thymosin beta-4 (~4963 Da), not with the Ac-LKKTETQ 7-mer that the word TB-500 denotes in commerce and in anti-doping science [7]. Where a finding below used the parent protein, it is marked as such. The fragment carries the actin-binding region, but whether it reproduces the full protein's effects at the doses used in peptide research has not been established in controlled human trials [7].
The dealt angle of this digest is the hair-follicle line. Thymosin beta-4 at nanomolar concentrations stimulated hair growth in rats and mice by activating hair-follicle bulge stem cells — increasing their migration and differentiation and raising MMP-2 expression [1]. That result has been corroborated across independent rodent studies [2][3]. It is animal data for the parent protein, and the site keeps it framed that way throughout. For the follicle-specific material, see the TB-500 hair growth research page; for how research peptide access is actually structured, see TB-500 legal status.
What is TB-500?
TB-500 is the synthetic N-acetylated heptapeptide Ac-LKKTETQ, corresponding to residues 17–23 — the actin-binding motif — of the 43-amino-acid protein thymosin beta-4 [6][7]. In commerce and veterinary contexts it carries the designations TB-500 and TB1000. It is a research/veterinary construct, not an endogenous human species and not an approved medicine [7].
The biology that draws attention to it belongs mostly to its parent. Thymosin beta-4 is the body's principal G-actin-sequestering peptide and a documented player in cell migration, angiogenesis, anti-inflammatory signaling and tissue repair across animal models [7]. The 7-mer carries the parent's actin-binding core; the open question is how much of the parent's activity the isolated fragment reproduces.
What does TB-500 stand for?
TB references thymosin beta-4, the parent protein; TB-500 is a research and veterinary designation for its synthetic Ac-LKKTETQ actin-binding fragment [7]. The numeric suffix is a product/lab designation, not a structural descriptor — it does not encode the residue count, the sequence, or a dose. The chemistry that matters is the sequence itself: Leu-Lys-Lys-Thr-Glu-Thr-Gln, N-acetylated, residues 17–23 of thymosin beta-4 [6].
TB-500 as a Research Peptide: the Ac-LKKTETQ Fragment
As a research peptide, the TB-500 peptide is supplied as a lyophilized powder for laboratory use, reconstituted in sterile or bacteriostatic water and kept refrigerated. Being a short acetylated peptide, it is more chemically robust than the full-length protein, but it remains subject to proteolysis and freeze-thaw degradation. Identity and purity of research-grade material — and specifically whether a vial contains the 7-mer or full-length thymosin beta-4 — are recurring concerns in unregulated supply.
The research peptide most often discussed alongside it is BPC-157; a 2026 Sports Medicine review lists TB-500/thymosin beta-4 and BPC-157 together among unapproved peptides with favorable animal-model tissue-repair outcomes but scarce human safety data [15]. The mechanistic anchor for TB-500 is the actin-sequestration mechanism: the LKKTETQ motif binds monomeric G-actin to buffer the unpolymerized pool and regulate cell migration [6].
TB-500 and Full-Length Thymosin Beta-4: the Identity Distinction
The single most important caveat on this site is an identity one. "TB-500" denotes the Ac-LKKTETQ heptapeptide (~889 Da), but the overwhelming majority of efficacy studies use full-length thymosin beta-4 (~4963 Da) [7]. The two are not interchangeable, and it is not established that the 7-mer reproduces the parent protein's effects [7].
A concrete consequence: full-length thymosin beta-4 is cleaved at its N-terminus to release Ac-SDKP, a separate fragment with its own anti-fibrotic and angiogenic activity — and that fragment is NOT produced by the C-terminal-region TB-500 sequence [7]. So even where the parent protein shows an effect, part of that effect may route through chemistry the 7-mer cannot generate.
This is not a pedantic distinction; it is the difference between the data and the label. When a product page cites a +61% re-epithelialization figure or a cardiac-survival result, those numbers were generated with the ~4963 Da protein, not the ~889 Da fragment in the vial [8][9][7]. The fragment carries the actin-binding motif and may well do something with it — the structural work is real [6] — but the burden of showing that the 7-mer reproduces the protein's measured effects has not been met in controlled human trials [7]. Every finding on this site that used full-length thymosin beta-4 is flagged as such. The wound-healing and tissue-repair studies carry this flag throughout, and so does the hair literature.