TB-500 Fragment 17-23

TB-500 Fragment 17-23 is a synthetic heptapeptide with the sequence Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH, written in single-letter code as LKKTETQ. It corresponds to residues 17 through 23 of thymosin beta-4, a 43-residue actin-binding peptide present in most mammalian cells. The N-terminal leucine carries an acetyl group and the C-terminal glutamine is a free acid. The compound has the molecular formula C38H68N10O14 and a molecular weight of 889.0 g/mol, and is catalogued in PubChem as CID 62707662 under CAS number 885340-08-9. Research material is supplied as a lyophilized (freeze-dried) solid, commonly as an acetate salt.

The name attached to this compound is the most common source of error in catalogs and in the literature. Material sold as TB-500 is sometimes the full 43-residue thymosin beta-4 (C212H350N56O78S, 4963 g/mol) and sometimes this seven-residue fragment, and the two differ by a factor of about 5.6 in formula weight. They are not interchangeable. Read the sequence and measured mass off the Certificate of Analysis for the lot in hand rather than relying on the product name. This entry covers the fragment; the full-length peptide is described at /encyclopedia/tb-500/.

Thymosin beta-4 was characterised in the 1980s as an intracellular actin-binding peptide. In 1996 Van Troys and colleagues mapped its actin-binding site by mutational analysis and identified a central region containing the LKKTETQ motif as a principal contact surface (PubMed 8617195). The isolated acetylated fragment is a synthetic construct built around that motif.

Short peptides containing the actin-binding domain have since been studied separately. Philp and colleagues investigated thymosin beta-4 and a synthetic peptide containing that domain in db/db diabetic and aged mice for effects on dermal repair endpoints (PubMed 12581423), and examined the same site in angiogenesis models (PubMed 14500546).

The evidence base for the isolated fragment is preclinical and thin: most published work uses the full-length peptide, few groups have tested short constructs, and there are no controlled human trials. Esposito and colleagues characterised the acetylated 17-23 fragment found in products labelled TB-500 (PubMed 22962027).

The mechanistic literature for this sequence derives from its parent peptide. Thymosin beta-4 is described as sequestering monomeric G-actin, and mutational mapping places the LKKTETQ region within the surface that contacts actin (PubMed 8617195). Reports on short constructs containing the motif describe effects on cell migration and vessel-formation endpoints in animal and cell-culture models (PubMed 14500546).

The distinction that matters most for study design is structural. The full peptide carries N-terminal and C-terminal segments flanking the central motif, and those segments contribute to the actin interface and to the intact molecule’s conformation. Results obtained with the 43-mer should not be assumed to transfer, and comparisons stated in mass rather than molar units misstate the relationship.

Published constructs also differ in terminal chemistry, acetylated or not, free acid or amidated, and papers naming TB-500 do not always specify which molecule was tested.

Sealed lyophilized material is held frozen at -20°C, shielded from light, in its original container. Lyophilized peptides are hygroscopic, meaning they take up water from the air, so a container reaches ambient temperature before it is opened. Repeated freeze-thaw cycles are avoided.

Stability for a lot is documented on its Certificate of Analysis.

Reconstitution means returning a lyophilized compound to solution. This entry gives no preparation procedure: solvent and concentration belong to a study protocol. The heptapeptide carries two lysine side chains and a glutamate side chain and is handled as aqueous-soluble material.

Lyophilized material absorbs atmospheric moisture, which degrades gravimetric accuracy. Water content, salt form and solubility data for a lot appear on its Certificate of Analysis.

Identity and purity are established analytically, typically by reverse-phase HPLC and mass spectrometry, with verified purity documented per lot on the Certificate of Analysis. For this compound the most useful single check is the observed mass: a value near 889 confirms the heptapeptide, while a value near 4963 indicates full-length thymosin beta-4 supplied under the same name.

Two further questions apply: whether the N-terminal acetyl group is present, since the unacetylated peptide has a different mass, and how much acetate salt and water the lot carries.

Related entries in this encyclopedia.

• TB-500.
  The full-length parent peptide sold under the same trade name, at /encyclopedia/tb-500/.
• BPC-157.
  Pentadecapeptide investigated in animal repair models, at /encyclopedia/bpc-157/.
• GHK-Cu.
  Copper-binding tripeptide studied in matrix-remodelling models, at /encyclopedia/ghk-cu/.
• Thymosin Alpha-1.
  A separate thymic peptide, unrelated in sequence.
• KPV.
  Another short fragment studied apart from its parent hormone.

Van Troys M, Dewitte D, Goethals M, et al. (1996). The actin binding site of thymosin beta 4 mapped by mutational analysis. EMBO J.
PubMed 8617195

Philp D, Badamchian M, Scheremeta B, et al. (2003). Thymosin beta 4 and a synthetic peptide containing its actin-binding domain promote dermal wound repair in db/db diabetic mice and in aged mice. Wound Repair Regen.
PubMed 12581423

Philp D, Huff T, Gho YS, et al. (2003). The actin binding site on thymosin beta4 promotes angiogenesis. FASEB J.
PubMed 14500546

Esposito S, Deventer K, Goeman J, et al. (2012). Synthesis and characterization of the N-terminal acetylated 17-23 fragment of thymosin beta 4 identified in TB-500. Drug Test Anal.
PubMed 22962027

TB-500 Fragment 17-23 is stocked here in one format: a sealed single-compound lyophilized vial from one supplier brand. Vials are the only listed format and the listed fill is 10mg. Per-vial strength is a product specification only. Each lot is batch tested with a published Certificate of Analysis documenting verified purity and the observed mass for that lot.

• Browse all TB-500 Fragment 17-23 research products
• Verified Peptides Frag (17-23) TB-500, 10mg lyophilized vial
• Collections: Research Vials. Documentation: COA and Lab Testing.

These products are sold for Research Use Only and are not intended for human consumption.