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biochemistry · three residues · two bonds

Tripeptide: definition, examples and calculator

A tripeptide is three amino acids joined by two peptide bonds, with two water molecules lost. From the 20 standard amino acids there are 20 × 20 × 20 = 8,000 possible tripeptides. Examples include glutathione, the copper-binding GHK (340.38 g/mol) and the hormone TRH.

Open Peptide Calculator editorial teamUpdated 9 sources

tripeptide_mw

sequence → formula and molecular weight

Modifications

Calculating…

Formula. MW = sum of residue masses + H2O (IUPAC atomic weights). The code and its checks are on the peptide calculator page.

What a tripeptide is

A tripeptide is a peptide of three amino acid residues joined by two peptide bonds; the prefix tri- counts the residues under IUPAC–IUBMB naming rules.[1] Forming it releases two molecules of water, one per bond. See what is a peptide bond.

How many tripeptides are possible?

8,000 linear tripeptides can be built from the 20 standard amino acids, because each of the three positions can hold any of the 20.

The rule is 20n possible chains of length n;[3] for n = 3 that is 20 × 20 × 20 = 8,000. The number counts each order separately (GHK and KHG are different) and leaves out side-chain links, D-amino acids and modified ends, all of which occur in real tripeptides below.

Tripeptide examples

Four tripeptides show the range: an antioxidant made in every cell, a copper-binding skin peptide, a fragment of a hormone, and a hormone that was once an approved drug.

Tripeptide examples
TripeptideSequenceFormulaMW (PubChem)Note
Glutathione[4]γ-Glu-Cys-GlyC10H17N3O6S307.33The first link runs through glutamate's side-chain (γ) carboxyl, an isopeptide bond[1]
GHK[5]Gly-His-LysC14H24N6O4340.38Binds copper as GHK-Cu, the "copper peptide"
KPV[6]Lys-Pro-ValC16H30N4O4342.43The last three residues of α-MSH
TRH (protirelin)[7][2]pGlu-His-Pro-NH2C16H22N6O4362.38Thyrotropin-releasing hormone; ring-closed first residue, amide end
  • Glutathione's γ-link does not change its formula. The linear α-sequence Glu-Cys-Gly gives the same C10H17N3O6S (307.32 g/mol calculated), which is why a sequence calculator matches PubChem within rounding.
  • TRH as a drug. Protirelin was FDA-approved as Thyrel TRH (NDA 018087), now listed as discontinued.[8] Its first residue is pyroglutamate, a ring formed from glutamine: Gln-His-Pro-NH2 is C16H25N7O4, and losing ammonia (NH3) on ring closure gives C16H22N6O4.
  • GHK and KPV have their own pages here: GHK-Cu and KPV, including their FDA status.

Calculate a tripeptide's molecular weight

Add the three amino acids and subtract two waters (2 × 18.02 g/mol), or let the calculator above do it from the one-letter code. GHK, for example, comes out at 340.38 g/mol and KPV at 342.44 g/mol, matching PubChem's 340.38 and 342.43 within rounding of the IUPAC atomic weights.[9]

What the calculator can modelThe 20 standard amino acids, an acetylated start, an amidated end and disulfide bonds. It cannot model pyroglutamate, β-amino acids or metal ions such as the copper in GHK-Cu; for those, start from its result and adjust as shown above.

Frequently asked questions

What is a tripeptide?

Three amino acids joined by two peptide bonds, with two molecules of water lost as they form.[1]

How many tripeptides are possible?

8,000 (20 × 20 × 20) from the 20 standard amino acids, counting each order separately.[3]

Is glutathione a tripeptide?

Yes: γ-glutamyl-cysteinyl-glycine. Its first link uses glutamate's side-chain carboxyl, so it is an isopeptide bond rather than the usual α-link.[4][1]

What is the copper tripeptide?

GHK-Cu, the tripeptide Gly-His-Lys bound to a copper ion, used in skin-care products. See the copper peptide serum page.

Sources

  1. IUPAC-IUB JCBN: Nomenclature and symbolism for amino acids and peptides, 3AA-11 to 3AA-13 (peptides, residues, peptide bonds) · IUPAC–IUBMB (web version, Queen Mary University of London), 1983 recommendations
  2. IUPAC-IUB JCBN: peptide symbolism, 3AA-18 and 3AA-19 (thyroliberin, glutathione) · IUPAC–IUBMB (web version, Queen Mary University of London), 1983 recommendations
  3. Alberts B et al. Molecular Biology of the Cell, 4th ed., chapter 3: The shape and structure of proteins · Garland Science, via NCBI Bookshelf, 2002
  4. PubChem CID 124886: glutathione · PubChem, NCBI, accessed November 13, 2026
  5. PubChem CID 73587: glycyl-L-histidyl-L-lysine (GHK) · PubChem, NCBI, accessed November 13, 2026
  6. PubChem CID 125672: KPV (Lys-Pro-Val) · PubChem, NCBI, accessed November 13, 2026
  7. PubChem CID 638678: protirelin (TRH) · PubChem, NCBI, accessed November 13, 2026
  8. Drugs@FDA: Thyrel TRH (protirelin), NDA 018087 (discontinued) · U.S. Food and Drug Administration, accessed November 13, 2026
  9. Abridged standard atomic weights 2024 · IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW), 2024