TB-500 - Frequently Asked Questions

TB-500 is a synthetic beta-thymosin-derived heptapeptide: an N-acetylated actin-binding fragment containing the WH2-motif LKKTET sequence. It corresponds to residues 17-23 of endogenous thymosin beta-4.

The sequence is Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH, abbreviated Ac-LKKTETQ. The leading Ac- is an N-terminal acetyl cap and the central LKKTET stretch is the conserved actin-binding motif.

The free base is approximately 889.0 g/mol with molecular formula C38H68N10O14. The acetate salt form is approximately 949.1 g/mol with formula C40H72N10O16 (PubChem CID 155977548). Use the matching molecular weight for molar calculations.

The CAS Registry Number is 885340-08-9, the unambiguous identifier used across supplier and chemical-database records to confirm the substance's identity.

In cell-free and cultured-cell systems, the parent thymosin beta-4 sequesters G-actin (monomeric actin) in a 1:1 complex, inhibits nucleotide exchange, and holds actin in a polymerization-incompetent state, buffering the pool of unpolymerized actin. TB-500 carries the LKKTET motif that mediates this actin contact. This is receptor-independent cytoskeletal biochemistry.

Mutational mapping by Van Troys et al. (EMBO J 1996, PMID 8617195) localizes the principal actin contacts to electrostatic interactions involving the LKKTET-motif lysines, such as Lys18, together with an N-terminal helix region.

In-vitro G-actin sequestration assays, F-actin polymerization kinetics in cell-free systems, cytoskeletal dynamics and cell-migration models in endothelial and fibroblast cultures, angiogenesis and endothelial tubule-formation models, structure-activity mapping of the LKKTET/WH2 motif, and comparative beta-thymosin family biochemistry.

No. The documented activity is direct protein-protein binding to actin monomers, not ligand-receptor signaling. The entry frames it as receptor-independent cytoskeletal and biochemical regulation in laboratory models only.

TB-500 here is described strictly as a research-use-only reference compound. All information is framed for in-vitro and cell-free laboratory contexts. No human dosing, therapeutic, or disease-treatment use is described or implied.

For in-vitro handling, the lyophilized powder is dissolved in bacteriostatic water, with the final concentration set by the diluent volume relative to the fixed peptide mass (concentration = mass / volume). Account for free base versus acetate salt molecular weight when preparing molar stocks. This is benchtop preparation, not a dosing protocol.

No measured half-life, clearance rate, or degradation constant is provided. Stability is discussed only through general principles: the N-acetyl terminal cap as a documented structural feature and standard short-peptide storage practice favoring lyophilized material and cold, single-use aliquots.

TB-500 is the isolated residues 17-23 fragment of thymosin beta-4, containing the LKKTET actin-binding motif. It is studied as the minimal motif-bearing determinant of the parent peptide's G-actin sequestration activity, and Philp et al. (FASEB J 2003, PMID 14500546) reported that this seven-amino-acid motif is required for angiogenic activity in endothelial cell models.