GHK-Cu is the copper(II) complex of the tripeptide glycyl-L-histidyl-L-lysine (GHK), also catalogued as prezatide copper or copper tripeptide-1. GHK was first described in 1973 as a tripeptide in human serum that prolonged the survival of normal liver cells in culture, and it has an affinity for copper(II) ions. Subsequent research has focused on connective tissue: collagen and glycosaminoglycan synthesis in fibroblast cultures, extracellular matrix accumulation and remodelling in rat wound chamber models, and, more recently, gene expression analyses. The presence of a GHK triplet in the alpha 2(I) chain of type I collagen has been noted as a possible source of the tripeptide at sites of tissue injury.