GHK-Cu Explained: Copper Tripeptide, CAS and Identifiers

GHK-Cu, the copper tripeptide explained

GHK-Cu is one of the more frequently misdescribed compounds in the research chemical market, largely because two closely related materials share a name. This page sets out what the compound is, how the copper complex forms, and which identifiers belong to which material.

What GHK is

GHK is a tripeptide. Three amino acids (glycine, L-histidine and L-lysine) in that order, written Gly-His-Lys. It was first described in human plasma in the early 1970s. On its own it is a small, water-soluble peptide with the molecular formula C14H24N6O4 and a molecular weight of 340.38 g/mol. Its CAS number is 49557-75-7.

How the copper complex forms

The histidine imidazole nitrogen, the deprotonated amide nitrogen and the N-terminal amine sit at positions that let three nitrogen donor atoms coordinate a single copper(II) ion. The result is a stable coordination complex. That is why GHK gets discussed as a copper-carrying peptide at all, and it is why the complexed and uncomplexed forms behave as two distinct materials in the laboratory. They have different masses, they behave differently in solution, and buffer composition affects them differently.

Why it is blue

The colour comes from a d-d electronic transition at the copper(II) centre, the same class of transition that makes copper sulfate blue. Its intensity varies with hydration state and with the geometry of the complex. That is why the shade of a lyophilised batch can run from deep blue to noticeably lighter with no difference in purity, and why colour is not a quality indicator.

The identifiers, and which one belongs to which material

Free tripeptide (GHK): CAS 49557-75-7, PubChem CID 73587, C14H24N6O4, 340.38 g/mol
Copper complex, neutral 1:1: PubChem CID 165429100, C14H22CuN6O4, 401.91 g/mol
Copper complex, cationic form (prezatide copper): CAS 89030-95-5, PubChem CID 71587328, C14H23CuN6O4+, 402.92 g/mol
2:1 species (bisprezatide copper): CAS 300801-03-0, PubChem CID 133697840, C28H48CuN12O8, 744.3 g/mol

A copper-complex product should be identified by CAS 89030-95-5. Listings carrying 49557-75-7 are quoting the free tripeptide. Because the complex is catalogued in several protonation states, quoted molecular weights differ by a unit or two between sources, which is expected. What is not interchangeable is the complexed versus uncomplexed material. Roughly 15% of the complex mass is copper and associated coordination, so 50mg of GHK-Cu does not contain 50mg of GHK.

How the material is characterised

Identity and purity are established by reverse-phase HPLC against a reference standard. A purity figure quoted without a stated method is not comparable between suppliers, since the number depends heavily on how it was measured.

Stability and storage

Lyophilised material, sealed, stored at -20°C in the dark and dry, is the stable presentation. Once in solution, degradation is faster and is driven by temperature, light, pH and any competing chelators present. That last point is specific to metal complexes. A stronger chelating agent will displace copper from the peptide, so buffer selection matters here in a way it does not for uncomplexed peptides.

Research use only

GHK-Cu is supplied by UK Peptides strictly as a laboratory research chemical. It is not a medicine. It is not for human or veterinary use, and it is not for use in food or cosmetics. We do not provide preparation, handling or usage guidance.