A tripeptide is a peptide consisting of three amino acids joined by peptide bonds. The exact nature and function of proteins is determined by the amino acids present and the order they occur. Simple examples are the tripeptides made by combining either three glycine molecules or two glycines and one alanine. The three glycine tripeptide can have only one structure: glycine-glycine-glycine. The other tripeptides can have different orders: glycine-alanine-glycine, glycine-glycine-alanine, and alanine-glycine-glycine. Each is a distinct molecule.
Examples of tripeptides are:
- Eisenin (pGlu-Gln-Ala-OH) is a peptide with immunological activity that is isolated from the Japanese marine alga, Eisenia bicyclis, which more commonly is known as, Arame
- GHK-Cu (glycyl-L-histidyl-L-lysine) is a human copper binding peptide with wound healing and skin remodeling activity, which is used in anti-aging cosmetics and more commonly referred to as copper peptide
- Glutathione (γ-L-Glutamyl-L-cysteinylglycine) is an important antioxidant in animal cells
- Isoleucine-proline-proline (IPP) found in milk products, acts as an ACE inhibitor
- Leupeptin (N-acetyl-L-leucyl-L-leucyl-L-argininal) is a protease inhibitor that also acts as an inhibitor of calpain
- Melanostatin (prolyl-leucyl-glycinamide) is a peptide hormone produced in the hypothalamus that inhibits the release of melanocyte-stimulating hormone (MSH)
- Ophthalmic acid (L-γ-glutamyl-L-α-aminobutyryl-glycine) is an analogue of glutathione isolated from crystalline lens
- Norophthalmic acid (y-glutamyl-alanyl-glycine) is an analogue of glutathione (L-cysteine replaced by L-alanine) isolated from crystalline lens
- Thyrotropin-releasing hormone (TRH, thyroliberin or protirelin) (L-pyroglutamyl-L-histidinyl-L-prolinamide) is a peptide hormone that stimulates the release of thyroid-stimulating hormone and prolactin by the anterior pituitary
- ACV (δ-(L-α-aminoadipyl)-L-Cys-D-Val) is a key precursor in penicillin and cephalosporin biosyntheses.