GHK and GHK-Cu: Two Registry Numbers, Two Masses, One Vial
GHK-Cu is one of the few compounds in a peptide catalogue that is not, strictly speaking, a peptide. It is a coordination complex: a tripeptide with a copper ion bound to it, and the two have different formulas, different masses and different registry numbers. That distinction is not pedantry. It decides what a 50mg or 100mg figure on a label refers to, and it changes how a certificate of analysis should be read.
Two registry numbers, and why both are correct
The free tripeptide glycyl-L-histidyl-L-lysine carries CAS 49557-75-7. The copper complex, named copper tripeptide-1 in cosmetic ingredient nomenclature, carries CAS 89030-95-5. A listing quoting either number is quoting a real substance; a listing quoting one number and supplying the other is describing something it is not selling. When comparing two suppliers, the registry number is the first thing to line up, because the names are used loosely and the numbers are not.
The tripeptide on its own
GHK is three residues: glycine, histidine, lysine, in that order, N-terminus to C-terminus. Its molecular formula is C14H24N6O4 and its monoisotopic mass is about 340.4 g/mol. It is a small, highly polar molecule, which is why it elutes early on a reversed-phase column and why its chromatography looks different from that of a longer, more hydrophobic peptide.
What the copper adds
The complex is C14H23CuN6O4, roughly 402.9 g/mol. Copper contributes about 63 of those daltons, and one hydrogen is lost when the metal binds, which is why the complex is not simply the peptide mass plus the metal mass. That missing hydrogen is a clue to how the binding works.
Where the copper actually sits
Copper(II) in this complex is held by three nitrogen donors from the peptide: the N-terminal amine of glycine, the deprotonated amide nitrogen of the glycine-histidine bond, and the imidazole nitrogen of the histidine side chain. Deprotonating that backbone amide is what releases the hydrogen and what makes the arrangement unusually stable for a small peptide. The lysine side chain is not part of the coordination sphere; it sits outside it, and it is the reason the complex remains highly water-soluble.
The colour is a real analytical signal
The complex is blue. That is not a dye and not an additive — it is the d-d absorption of copper(II) in this ligand field, and it appears at around 620 nm. A vial of GHK-Cu that reconstitutes colourless is worth questioning, because the colour is a property of the complex rather than of the container. It is the only compound in most catalogues where the eye is a first-pass identity check.
What a 50mg or 100mg figure refers to
This is where the two masses matter commercially. If a label figure refers to the complex, then a 100mg vial holds roughly 84mg of tripeptide and roughly 16mg of copper. If it refers to the free peptide, the total mass in the vial is higher. Neither convention is dishonest, but they are not interchangeable, and comparing a price per milligram across two suppliers using different conventions produces a number that means nothing. The general version of this problem is covered in comparing peptide prices per milligram.
Purity of a complex is not purity of a peptide
An HPLC purity figure for GHK-Cu describes the peak area of the complex against everything else the detector recorded. It does not, on its own, establish that the copper is fully coordinated. Partially complexed material and free tripeptide can appear as separate peaks, and a certificate that resolves them is telling you more than one that reports a single number. Copper content itself is a separate determination — typically by atomic absorption or ICP — and it is not part of a routine peptide certificate. What is and is not on a standard report is set out in what third-party peptide testing measures.
How it is written
The same material appears as GHK-Cu, GHKCu, GHK copper peptide, copper tripeptide-1, and occasionally as the copper peptide. All of them refer to the complex described above. GHK on its own, without the copper, refers to the free tripeptide and is a different item with a different registry number.
Stability, and what actually degrades it
The complex is stable as a lyophilised solid and less so in solution, where the relevant variables are pH and competing ligands rather than temperature alone. Copper coordination is pH-dependent, and a buffer containing a stronger chelator will strip the metal from the peptide given the chance. That is a reason to be deliberate about reconstitution solvent rather than defaulting to whatever is nearest; the general considerations are in choosing a reconstitution solvent, and the storage side in storage and stability of lyophilised peptides.
Reading the certificate for this compound
Three things are worth locating on a GHK-Cu report. The registry number, so you know which substance was tested. The detection wavelength, because a small polar tripeptide analysed at the wrong wavelength gives a purity figure that flatters it. And the mass, so you can confirm the analysis was run on the complex rather than on the free peptide. Every report we hold is published in full on the certificates of analysis page.
What we supply
GHK-Cu is stocked as a 100mg vial and a 50mg vial, lyophilised, with the identity data and registry numbers published on each product page. It is supplied for laboratory research use only, and we publish no dosing information, no protocols involving human or veterinary subjects, and no statements about what the compound does in a person.
