GHK-Cu is three amino acids joined together, glycine then histidine then lysine, holding a single copper ion. The three amino acids on their own are called GHK; add the copper and it becomes GHK-Cu, and the two are different substances that do not always behave the same way. The tripeptide was first found in human blood plasma. Research on it has centered on skin cells and the material they build around themselves, and on lung tissue in animals.