Glossary
Peptide
A peptide is a chain of amino acids linked by peptide bonds. Where the line to proteins is drawn, and what the word peptide on a vial label does not tell you.
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. Almost everything in a research peptide catalogue lies far below it: GHK-Cu and KPV are tripeptides, 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, adding one residue at a time starting from the C-terminus; longer or glycosylated molecules are generally produced recombinantly. The production route defines which impurities a lab will encounter — deletion sequences, incomplete deprotection, oxidised residues — as well as the counter-ion (typically acetate or trifluoroacetate) that comes with the powder.
What a label cannot tell you
The word "peptide" on a vial reveals nothing about identity, net peptide content or salt content. Two vials bearing the same sequence name may differ in their modifications (amidation, acetylation) and in their impurity pattern. Proof comes from HPLC purity together with a matching mass spectrometry result, both reported for the specific lot on a certificate of analysis. All material.
Related terms
amino acid · peptide bond · purity. Browse all research peptides or start with BPC-157.