GHK-Cu in the USA: Two CAS Numbers on One Product
GHK-Cu is one of the few things in a peptide catalog that is not, strictly, a peptide. It is a coordination complex — a tripeptide with a copper ion bound to it — and the peptide and the complex have different formulas, different masses and different registry numbers. That is not pedantry. It determines what a 50mg or 100mg figure on a label actually refers to, and it changes how the certificate should be read.
Two registry numbers, both correct
The free tripeptide glycyl-L-histidyl-L-lysine is CAS 49557-75-7. The copper complex, called copper tripeptide-1 in cosmetic ingredient nomenclature, is CAS 89030-95-5. A listing quoting either number is naming a real substance; a listing quoting one and shipping the other is describing something it is not selling. When comparing suppliers the registry number is the first thing to line up, because the names are used loosely and the numbers are not.
The tripeptide by itself
Three residues — glycine, histidine, lysine, N-terminus to C-terminus. Molecular formula C14H24N6O4, monoisotopic mass about 340.4 g/mol. It is small and highly polar, which is why it elutes early on a reversed-phase column and why its chromatography looks nothing like that of a longer, more hydrophobic peptide.
What the metal adds
The complex is C14H23CuN6O4, around 402.9 g/mol. Copper accounts for roughly 63 of those daltons, and one hydrogen is lost when the metal binds — which is why the complex is not simply peptide mass plus metal mass. That missing hydrogen is a clue to how the binding works.
Where the copper sits
Copper(II) 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 it is what makes the arrangement unusually stable for a peptide this small. The lysine side chain takes no part in the coordination sphere; it sits outside it, and it is why the complex stays so water-soluble.
The color is a genuine analytical signal
The complex is blue, and the blue is not a dye or an additive. It is the d-d absorption of copper(II) in this ligand field, centered around 620 nm. A vial of GHK-Cu that reconstitutes colorless is worth a question, because the color belongs to the complex rather than to the container. It is the one compound in most catalogs where the eye works as a first-pass identity check.
What a 50mg or 100mg figure refers to
Here is where the two masses matter commercially. If the label figure describes the complex, a 100mg vial holds roughly 84mg of tripeptide and roughly 16mg of copper. If it describes the free peptide, the total mass in the vial is higher. Neither convention is dishonest, but they are not interchangeable, and a price-per-milligram comparison across two suppliers using different conventions produces a number that means nothing at all. The general form of this problem is 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 saw. On its own it does not establish that the copper is fully coordinated. Partially complexed material and free tripeptide can show as separate peaks, and a certificate that resolves them is telling you more than one reporting a single number. Copper content is a separate determination altogether — usually atomic absorption or ICP — and it is not part of a routine peptide certificate. What is and is not on a standard report is covered in what third-party peptide testing measures.
Names you will see
GHK-Cu, GHKCu, GHK copper peptide, copper tripeptide-1, and sometimes just the copper peptide. All refer to the complex described here. GHK on its own, without the copper, is the free tripeptide and a different item with a different registry number.
Stability, and what actually degrades it
The complex is stable as a lyophilized solid and less so in solution, where the variables that matter 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 off the peptide given the opportunity. That is a reason to choose the reconstitution solvent deliberately rather than reaching for whatever is closest; the general considerations are in choosing a reconstitution solvent, and the storage side in storage and stability of lyophilized peptides.
Reading the certificate for this one
Three things to locate on a GHK-Cu report. The registry number, so you know which substance was tested. The detection wavelength, because a small polar tripeptide analyzed at the wrong wavelength produces a purity figure that flatters it. And the mass, so you can confirm the analysis ran 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, lyophilized, with identity data and registry numbers published on each product page. Supplied for laboratory research use only; we publish no dosing information, no protocols involving human or veterinary subjects, and no statements about what the compound does in a person.