TB-500 (Frag)

Format: lyophilised vial, 2 mg. One sealed vial of freeze-dried TB-500 (Frag), the N-acetylated heptapeptide Ac-LKKTETQ (thymosin β4 residues 17–23), prepared in the laboratory as a solution at the concentration the protocol requires. Looking for fixed, pre-weighed units of the same molecule? That is a separate product: TB-500 Capsules.

Thymosin β4 is a 43-residue actin-sequestering protein, but much of its contact with actin runs through a short central stretch, residues 17–23. TB-500 (Frag) is the synthetic, N-terminally acetylated version of that stretch: the heptapeptide Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln (Ac-LKKTETQ). Analytical laboratories identified this molecule as the active ingredient of preparations sold under the name “TB-500” (Esposito et al., 2012; Ho et al., 2012). It is a different molecule from full-length thymosin β4, which Condor Research lists separately as TB-500 (10 mg vial); the same fragment is also available as a pre-weighed solid in TB-500 Capsules.

Why a seven-residue motif. Mutational mapping placed part of thymosin β4’s actin-binding site in the motif that begins at residue 17 (Van Troys et al., 1996). A review of the protein’s short active sequences attributes its cell-migration, angiogenic and wound-repair activity to the LKKTETQ region — distinct from the N-terminal tetrapeptide Ac-SDKP, whose literature concerns fibrosis and inflammation and which is not this product (Sosne et al., 2010).

What the research explores. The literature on the isolated heptapeptide is small, and most of it used the non-acetylated sequence:

• Endothelial migration and vessel sprouting (in vitro / ex vivo) — the actin-binding motif matched full thymosin β4 in human umbilical vein endothelial cell migration and chick aortic-arch sprouting assays, while peptides lacking it were inactive (Philp, Huff et al., 2003).
• Dermal wound models (animal) — a synthetic LKKTETQ peptide promoted repair in aged mice to a degree comparable with the parent protein (Philp, Badamchian et al., 2003).
• Hepatic stellate cells (in vitro) — the 17–23 peptide, but not the 1–15 peptide, blunted PDGF-BB-driven activation markers, proliferation and migration in human cell cultures (Shah et al., 2018).
• Metabolism and detection (in vitro, rat, horse) — LC-MS methods identify Ac-LKKTETQ and metabolites such as Ac-LK and Ac-LKK in plasma and urine (Ho et al., 2012; Kwok et al., 2013; Rahaman et al., 2024).

What the evidence does not show. Rahaman et al. (2024) note that the biological effects of the acetylated form itself had not been documented; in their fibroblast assay only the metabolite Ac-LKKTE, not the parent heptapeptide, showed significant wound-closure activity. The human clinical studies often cited in discussions of TB-500 used full-length thymosin β4 — an ophthalmic solution (RGN-259) and a topical formulation in venous ulcers — not this fragment (Sosne & Ousler, 2015; Guarnera et al., 2010). There are no human data for Ac-LKKTETQ, and the findings above do not establish safety or efficacy in humans. Full citations are listed under the Scientific References tab.

Which “TB-500” is which. The name is used in the market for more than one molecule; sequence, mass and CAS number, not the trade name, identify what is in the vial.

Physicochemical profile. CAS 885340-08-9 · Molecular formula C₃₈H₆₈N₁₀O₁₄ · Molecular weight 889.0 g/mol · Sequence Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln (thymosin β4 residues 17–23, N-terminally acetylated) · Appearance: white lyophilized powder · Soluble in water.

Specification & quality. Each individually sealed vial contains 2 mg of TB-500 (Frag) — Ac-LKKTETQ — as a white lyophilized powder at ≥99% purity by HPLC. Every batch is third-party tested, with a Certificate of Analysis (COA) available. Store at −20 °C, protected from light and moisture.

This product is intended for laboratory research use only (RUO). It is not a drug, food, cosmetic, or dietary supplement, and is not for human or veterinary use, ingestion, or diagnostic application. Handling is restricted to qualified research professionals operating in an appropriately equipped laboratory.

When the TB-500 (Frag) lyophilised vial is the right format

• One quantity, concentration chosen at the bench. The 2 mg cake (about 2.25 µmol at 889.0 g/mol) is reconstituted with a suitable diluent, so the working concentration follows the assay and not a fixed unit mass.
• Reference-standard work. Detection work on this heptapeptide (Esposito et al., 2012; Ho et al., 2012) is done by LC-MS on solutions; a vial supplies the single reference quantity from which a stock and its dilution series are prepared.
• Storage before and after preparation. Keep the sealed vial at −20 °C, protected from light and moisture; in solution, stability depends on the diluent and the temperature, which is why a vial suits stock prepared on demand.

Need identical pre-weighed units for replicate or blinded designs? TB-500 Capsules hold the same molecule (60 × 500 mcg per bottle) and are sold separately. Both formats carry the fragment, not the full-length thymosin β4 of the TB-500 10 mg vial. For laboratory research use only. Not for human or veterinary use.

Research overview: TB-500 (Full-Length Thymosin β4) vs TB-500 Fragment: One Name, Two Different Molecules