TB-500 (Thymosin β-4 fragment) — wholesale 10-vial kits

Research context

Thymosin β-4 (Tβ4) is a 43-residue, N-acetylated protein of about 4,963 Da and the main G-actin-sequestering molecule in mammalian cells. It was first sequenced from bovine thymus in 1981 and thought to be a thymic hormone; a decade later the actin-sequestering platelet peptide known as Fx was shown to be the same molecule (Safer et al., Journal of Biological Chemistry, 1991), which reframed it as a cytoskeletal protein. Its central LKKTET motif binds actin, and short peptides containing that motif reproduce several of the full protein's effects on cell migration in experimental models.

Structure–function of the fragment. Tβ4 binds G-actin at a 1:1 ratio and thereby blocks its polymerization to F-actin, a property measured with the DNase I inhibition assay. Digestion studies showed that oxidation of the single methionine at position 6 does not abolish actin sequestration, but fragments beginning at residue 13 or 24 do not inhibit polymerization at all, so structural features in the region before residue 13 are required for that function (Hannappel et al., 1993). Mapping work on the full protein assigned separate activities to separate sites: the N-terminal region containing Ac-SDKP to cell-survival effects, and the central actin-binding domain LKKTET (residues 17–22) plus the adjacent glutamine to cell migration and angiogenesis in model systems (Goldstein et al., FASEB Journal, 2010). Ac-LKKTETQ, the peptide usually sold as TB-500, is exactly that heptapeptide with an N-terminal acetyl group.

Naming matters here. "TB-500" is used in the market for two different molecules: full-length Tβ4 and the much smaller Ac-LKKTETQ fragment (about 889 Da). Both can show high HPLC purity; only the mass on the COA tells them apart. The PubChem record on this page is the fragment, and the LC-MS mass on each lot's COA states which molecule that lot contains.

Researchers use Tβ4 and its fragments in actin-dynamics, endothelial and keratinocyte migration, and cardiac and dermal tissue-repair models in rodents. Analytical chemists know the fragment from anti-doping work: Ac-LKKTETQ was identified in commercial TB-500 material by high-resolution Orbitrap mass spectrometry, synthesized independently by solid-phase synthesis for confirmation, and then used to build triple-quadrupole LC-MS methods for plasma and urine (Esposito et al., Drug Testing and Analysis, 2012). Equine doping-control laboratories have published their own LC-MS methods and population studies for Tβ4 and this fragment, which makes it a recurring reference material in that field.

U.S. regulatory status: TB-500 is not an FDA-approved drug. In FDA's compounding records, "thymosin beta-4, fragment (LKKTETQ), also known as TB-500" appears among the nominated bulk drug substances with identified potential significant safety risks, with FDA citing immunogenicity risk from aggregation, peptide-related impurities, and the absence of identified human exposure data for the fragment. TB-500-related bulk drug substances were on the agenda of FDA's Pharmacy Compounding Advisory Committee meeting of 23–24 July 2026, and on 30 October 2026 HHS published notice of an enforcement discretion policy for 503A compounding using certain peptide bulk drug substances while the 503A bulks list goes through rulemaking. That notice is a statement of enforcement intent rather than an approval. WholesalePeptide.us supplies TB-500 only for in-vitro, analytical and preclinical laboratory research.

Labs that need a specific molecule should check the COA mass before ordering at volume; if you need the full-length 43-residue protein rather than the fragment, contact us before placing a 100+ kit quote so the correct material is reserved. TB-500 is also available pre-blended with BPC-157, and in the GLOW blend with BPC-157 and GHK-Cu, for labs studying combinations of these peptides in tissue-repair models.

Research areas

• G-actin sequestration and actin dynamics
• DNase I inhibition assays of actin binding
• Cell-migration assays (endothelial, keratinocyte)
• Cardiac and dermal tissue-repair models in rodents
• LC-MS detection methods for Tβ4 fragments

U.S. regulatory status of the compound (as an active ingredient): Not FDA-approved. The material sold here is a research reference chemical, not a drug product.

Handling and storage

• Store lyophilized vials at −20 °C, sealed, protected from light and moisture.
• Let the vial reach room temperature before opening to limit condensation on the powder.
• Reconstitute in a sterile buffer appropriate to the assay, following your lab's SOP.
• Aliquot reconstituted material and freeze once; avoid repeated freeze–thaw.