A tripeptide is a peptide of three amino acid residues joined by two peptide bonds, typically 250-500 Da. Despite the minimal size, tripeptides include several of the most studied bioactive sequences in the catalog.
Examples that define the class
GHK (Gly-His-Lys), isolated from human plasma by Loren Pickart in 1973, chelates copper(II) through its histidine imidazole and N-terminal amine to form GHK-Cu — the metal complex, not the free peptide, carries most of the reported activity. KPV (Lys-Pro-Val) is the C-terminal tripeptide of alpha-MSH and retains anti-inflammatory readouts without melanocortin receptor pigmentation effects. Glutathione is a tripeptide with an unusual gamma-glutamyl linkage that makes it resistant to ordinary aminopeptidases. TRH (pGlu-His-Pro-NH2) shows how N- and C-terminal capping stabilises a three-residue hormone.
Handling follows from size: tripeptides are cheap and clean to synthesise, give simple HPLC traces, and have short circulating half-lives unless modified. Palmitoylation — as in Palmitoyl Tripeptide-1 — is the standard route to make one lipophilic enough for topical formulation.
Related terms and material
tetrapeptide · half-life · matrikine. Reference material: GHK-Cu, KPV, Palmitoyl Tripeptide-1. Further reading: what is GHK-Cu.