Peptide Fragments: BPC-157, TB-500 and Related Sequences

BPC-157 is GEPPPGKPADDAGLV, a 15-residue sequence described as a stable fragment of a protein found in gastric juice. It contains no methionine, cysteine or tryptophan, so it lacks the residues most prone to oxidation, and its four prolines make it unusually resistant to proteolysis. No specific receptor has been identified for it. TB-500 is Ac-LKKTETQ, residues 17 to 23 of thymosin beta-4 with an acetylated N-terminus (CAS 885340-08-9, about 889 g/mol). This is the actin-binding motif of the full 43-residue protein, and findings on the full-length protein do not automatically transfer to the fragment. GHK-Cu is the tripeptide glycyl-L-histidyl-L-lysine complexed with copper(II).

Work on thymosin beta-4 and its fragment centres on G-actin sequestration: the LKKTETQ motif binds monomeric actin and regulates its polymerisation, measured in pyrene-actin assays and cell migration assays in culture. Studies of BPC-157 report interaction with the nitric oxide pathway and changes in VEGFR2 and FAK-paxillin signalling in endothelial and fibroblast cell culture; because no receptor is known, these are pathway observations rather than a defined binding event. GHK binds copper(II) with high affinity through the histidine imidazole and the N-terminal amine, and studies of the complex measure gene-expression changes in cultured cells.

Identity is established by mass spectrometry: an intact mass, or a precursor and fragment transition (MRM) matched against a reference standard, confirms that the sequence in the vial is the one on the label. Purity is a chromatographic figure, the principal peak area by reversed-phase HPLC, and it bounds peptide-related impurities only; it says nothing about counterion, water or residual solvent content, which is why net peptide content is reported separately. Lyophilised material is stored cold, dry and dark, and a certificate states what was measured on one named lot. For TB-500 the certificate should confirm the heptapeptide specifically: its doubly charged precursor sits near m/z 445, and a mass near 4,963 Da would indicate the full-length protein instead. Blends of these sequences are characterised compound by compound, so a blend certificate reports a purity and a mass for each component rather than one figure for the vial.

The BPC-157 literature is dominated by a single research group and by rodent models, and some papers have been withdrawn; treat an unreplicated result as a hypothesis. Much of what is published as "TB-500" research was performed with full-length thymosin beta-4, so check which molecule a paper used before citing it for the fragment. Regulatory status differs by jurisdiction, and none of these compounds is an approved drug in Canada or the United States.