Peptide

Peptides are chains of amino acids connected by peptide bonds, by convention containing from 2 up to about 50 residues. Beyond roughly 50 residues the same type of molecule is normally called a protein, although this cut-off is a naming habit and not a chemical law. Nearly all catalogue compounds sit well under that line: KPV and GHK-Cu have three residues each, BPC-157 is a pentadecapeptide of 15 residues, and semaglutide is a GLP-1 analog of 31 residues bearing a fatty-acid side chain.

Why chain length matters

The length of a sequence determines how it is manufactured and what its documentation ought to include. Short and medium sequences are built by solid-phase peptide synthesis, which extends the chain residue by residue from the carboxy end; for long or glycosylated molecules, recombinant expression is usual. The production route defines which impurities a lab will encounter — oxidised residues, missing-residue sequences, leftover protecting groups — as well as the counter-ion (typically acetate or trifluoroacetate) that comes with the powder.

What a label cannot tell you

Seeing "peptide" on a label tells you neither what the molecule is, nor how much of the powder is peptide, nor how much is salt. Two vials bearing the same sequence name may differ in their modifications (amidation, acetylation) and in their impurity pattern. Evidence means an HPLC purity value plus a matching MS mass, both reported per lot on the COA. This applies to all material.

Related terms

See also purity, amino acid and peptide bond. Explore the full catalogue, for instance beginning with BPC-157.