TB-500

TB-500 is supplied as thymosin beta-4, a 43-residue N-terminally acetylated peptide and the principal G-actin sequestering molecule in mammalian cells. The name is used commercially for both the full-length peptide and for the shorter LKKTETQ heptapeptide derived from it; the full-length sequence is the dominant commercial identity and is what is offered here.

Its molecular function is well defined. The peptide binds monomeric G-actin in a one-to-one complex and holds it in a polymerisation-incompetent state, thereby buffering the pool of actin available for filament assembly. The central LKKTETQ motif is the actin-binding determinant, which is why that fragment alone retains a portion of the reported activity. The peptide is intrinsically disordered in isolation and adopts helical structure only upon binding actin.

Because the actin interaction is directly measurable, the in-vitro literature is more quantitative than for most peptides of comparable research interest. Pyrene-actin polymerisation assays measure sequestration directly by tracking fluorescence as monomers are withdrawn from the polymerising pool, and binding stoichiometry has been established by titration.

Downstream work uses cell migration and scratch-closure assays in fibroblast and endothelial preparations, where cytoskeletal turnover governs the readout, alongside endothelial tube-formation assays examining angiogenic signalling. The peptide is strongly acidic and intrinsically disordered, which is why structural work has relied on complexes with actin rather than on the free peptide.

Reversed-phase HPLC establishes purity and mass spectrometry confirms identity, reported per lot on the Certificate of Analysis, with attention to the 42-dalton increment that distinguishes the N-terminally acetylated peptide from the unacetylated form.

At 43 residues this is a long solid-phase synthesis, so deletion sequences are the dominant impurity class, and on a molecule of this size a single missing residue is a small relative mass shift that chromatography resolves more reliably than a routine mass check. The sequence contains no cysteine, so disulfide-related impurities do not arise. The strongly acidic character makes adsorption loss to container surfaces a practical concern at low working concentrations, which low-binding labware mitigates.