What is a tripeptide?
A tripeptide is three amino acids joined by two peptide bonds. Some of the best-known molecules in biochemistry are tripeptides, glutathione and GHK among them. Here is how one forms, how to name it and weigh it, and real examples with their PubChem records.
Three residues, two peptide bonds.
Each peptide bond joins the carboxyl group of one amino acid to the amino group of the next and removes one water (IUPAC-IUB rules 3AA-11 and 3AA-12). A tripeptide has three residues and two such bonds, so two waters are lost. Triglycine shows it: three glycines, C2H5NO2 each, minus two H2O give C6H11N3O4, 189.17 g/mol. See the peptide bond guide and the dipeptide guide for the one-bond case.
8,000 possible sequences.
Names run from the N-terminus to the C-terminus, with every residue except the last ending in -yl: glycyl-histidyl-lysine is Gly-His-Lys, or GHK in one-letter code. Because order matters and residues can repeat, the 20 standard amino acids give 20 × 20 × 20 = 8,000 possible tripeptides.
IUPAC's own example is glutathione, named γ-glutamylcysteinylglycine. The gamma marks a bond through glutamate's side-chain carboxyl rather than its alpha-carboxyl, an isopeptide bond.
Working out the weight.
Add the three free amino acids and subtract two waters. For GHK: glycine 75.07 + histidine 155.15 + lysine 146.19 − 2 × 18.015 = 340.38 g/mol, exactly PubChem's value. The molecular weight calculator does it from the sequence, and the isoelectric point calculator gives GHK's charge at any pH.
Six well-known tripeptides.
| Tripeptide | Sequence | Formula | MW (g/mol) | PubChem CID | Note |
|---|---|---|---|---|---|
| Triglycine | Gly-Gly-Gly | C6H11N3O4 | 189.17 | 11161 | The simplest tripeptide |
| Glutathione (reduced) | γ-Glu-Cys-Gly | C10H17N3O6S | 307.33 | 124886 | Gamma (isopeptide) link; the most abundant non-protein thiol in mammalian tissues |
| GHK | Gly-His-Lys | C14H24N6O4 | 340.38 | 73587 | Binds copper(II) as a 1:1 complex, GHK-Cu |
| KPV | Lys-Pro-Val | C16H30N4O4 | 342.43 | 125672 | Residues 11-13 of alpha-MSH (free acid record) |
| Thyrotropin-releasing hormone | pGlu-His-Pro-NH2 | C16H22N6O4 | 362.38 | 638678 | Both ends capped: pyroglutamyl ring and prolinamide |
| Ala-Glu-Asp | Ala-Glu-Asp (AED) | C12H19N3O8 | 333.29 | 87815447 | Listed as "Cartalax" among the Khavinson peptides |
Formulas, weights and CIDs from PubChem (read 11/2026). Only GHK, as GHK-Cu, is a Helion product.
When a tripeptide has no free ends.
Thyrotropin-releasing hormone shows how much the ends matter. Its N-terminal glutamate is cyclized into a pyroglutamyl ring and its C-terminus is an amide, so it has neither a free amine nor a free acid. A 1969 paper identified the hormone as pyroglutamyl-histidyl-proline amide. Caps like these change a peptide's mass, charge and stability; the N-terminus vs C-terminus guide covers them.
How cells take up tripeptides.
Like dipeptides, tripeptides cross cell membranes on the proton-coupled carriers PEPT1 (gene SLC15A1) and PEPT2 (SLC15A2), which handle di- and tripeptides but not free amino acids or longer chains. The dipeptide guide covers the same transporters.
The tripeptide in Helion's catalog.
GHK binds copper(II) tightly. A 1982 solution study showed a 1:1 complex at neutral pH in which the histidine ring nitrogen is one of the copper ligands, and that complex is what gives GHK-Cu its deep blue colour; see why GHK-Cu is blue and AHK-Cu vs GHK-Cu.
GHK-Cu, tested by lot.
Helion sells GHK-Cu 50mg (vial code CU50); lot CU501 tested 99.90% HPLC purity at ILS Laboratories, and the report is in the COA Portal. Helion supplies these compounds as lyophilized research reference materials for laboratory use only, to buyers 21 and over.
Specs and storage by compound.
Questions (6)
What is a tripeptide?
Three amino acids joined by two peptide bonds. Two molecules of water are lost in forming it, so it weighs the sum of its three amino acids minus about 36.03 g/mol.
How many tripeptides are possible?
From the 20 standard amino acids, 8,000 (20 x 20 x 20), because order matters and residues can repeat.
What are examples of tripeptides?
Glutathione (gamma-Glu-Cys-Gly), GHK (Gly-His-Lys), KPV (Lys-Pro-Val), thyrotropin-releasing hormone (pGlu-His-Pro-NH2) and triglycine (Gly-Gly-Gly).
Is glutathione a tripeptide?
Yes. It is gamma-glutamyl-cysteinyl-glycine; the first bond runs through glutamate's side-chain (gamma) carboxyl, an isopeptide bond.
Is GHK-Cu a tripeptide?
GHK is a tripeptide, glycyl-histidyl-lysine. GHK-Cu is that tripeptide bound to a copper(II) ion as a 1:1 complex.
What is the difference between a tripeptide and a polypeptide?
A tripeptide has exactly three residues. A polypeptide is a longer chain, usually more than about 10 to 20 residues.
Published studies (4)
- Glutathione synthesis
- Structure of the Glycyl-L-histidyl-L-lysine--copper(II) complex in solution
- The identity of chemical and hormonal properties of the thyrotropin releasing hormone and pyroglutamyl-histidyl-proline amide
- The proton oligopeptide cotransporter family SLC15 in physiology and pharmacology
Citations from PubMed for reference. They describe the compound in the literature, not any Helion lot, and nothing here is guidance on use.