GHK-Cu is usually filed alongside the other peptides in a catalogue, and that is misleading. It is a coordination complex: a three-residue peptide holding a copper ion. The metal is part of the compound, and it changes what a certificate has to prove.
Two things with two sets of numbers
The peptide on its own is glycyl-L-histidyl-L-lysine, which is where the letters come from.
- GHK, free tripeptide: C14H24N6O4, about 340 g/mol, CAS 49557-75-7, PubChem CID 73587.
- The copper complex: CAS 89030-95-5, listed in PubChem as C14H23CuN6O4+ at about 403 g/mol (CID 71587328).
Notice that the complex is written as a cation. That is not a typographical quirk, and it is the first thing worth understanding about this material.
Why the formula moves around
A peptide has one formula. A metal complex's written formula depends on how you account for it: whether the peptide is deprotonated at the nitrogen that binds the metal, what the overall charge is, which counterion balances it, and whether the entry describes one peptide per copper or two. Different databases and suppliers resolve those choices differently, which is why you will see several formulas and several masses attached to the same name.
For an ordinary peptide, the name plus the sequence effectively defines the material. For this one it does not, so the certificate is carrying more weight than usual.
How the copper is held
Short peptides with a histidine near the amino terminus are a well known class of copper binders, because several donor atoms can be brought into position around the metal at once. (Reference: Harford & Sarkar, 1997) For this particular tripeptide, the geometry of the copper complex in solution was worked out in 1982, and the binding involves the terminal amine, the imidazole of the histidine and a backbone nitrogen, with the metal held in a roughly planar arrangement. (Reference: Freedman et al., 1982)
Binding a metal through a backbone nitrogen requires that nitrogen to lose its proton, which is why the complex carries a different charge from the free peptide and why pH matters to how the species is distributed. Our note on copper peptides introduces the family, and AHK-Cu is a related complex built on a different tripeptide.
The copper leaves a fingerprint
This compound is easier to verify than most, if the method is right. Copper has two stable isotopes, copper-63 and copper-65, present in nature at roughly 69 and 31 percent. Any species that contains a single copper atom therefore shows a pair of peaks two mass units apart in that ratio.
That pattern is hard to fake and easy to read. A mass spectrum of genuine material shows it; a spectrum of the free peptide with no metal does not. It is one of the few cases where the identity measurement carries a built-in internal check.
The one thing you can see
Almost nothing about a research peptide is visible to the eye. This compound is the exception, up to a point. Copper(II) complexes with nitrogen donors absorb in the visible range, so the material is coloured, while the free tripeptide is not. A vial of genuine complex does not look like a vial of white powder.
That is a useful sanity check and nothing more. Colour tells you a copper species is present; it does not tell you the stoichiometry, the purity of the peptide, or whether the complex is the intended one. Treat it the way you would treat a seal on a box: worth noticing if it is wrong, not evidence of much if it is right.
Why purity alone tells you less here
A purity percentage from reversed-phase chromatography answers a question about the peptide: what share of the detected material was the target sequence. It does not, on its own, tell you how much copper is present or whether it is bound in the intended one-to-one ratio.
There is also a methodological trap. Reversed-phase methods for peptides normally run at low pH with an acidic additive, and acidic conditions can shift a labile metal complex toward its dissociated form. A run that reports a clean peak may be reporting a clean peak of the free tripeptide. For a metal complex, then, the conditions of the analysis are part of the result in a way that goes beyond the usual, and copper content is worth reporting as its own figure rather than inferred from peptide purity. Our guide to reading a certificate covers what a complete document carries.
Where the sequence comes from
Unlike engineered agonists, GHK is a sequence that occurs naturally in human plasma. The research-grade material is made synthetically by solid-phase synthesis and then complexed with copper under controlled conditions, so the ratio and the purity are defined rather than inherited. Natural origin is part of the story; it is not a substitute for a batch record.
This is laboratory work. GHK-Cu is supplied strictly as a research compound, and nothing here describes use in people or animals.
Handling and verification
Material ships lyophilized and the usual rules apply: dry, cool, away from light, and let a cold vial warm before opening so condensation does not form inside. Any Codex Research vial can be checked against its paperwork by batch number.
Research use only
All products sold by Codex Research, including GHK-Cu, are strictly for laboratory research and development. They are not for human or animal consumption and are not intended to diagnose, treat, cure, or prevent any disease.
The compound at Codex Research
GHK-Cu, 100 mg per vial · batch-verified, with its certificate of analysis.
Frequently asked questions
What is GHK-Cu?
A coordination complex of the tripeptide glycyl-L-histidyl-L-lysine with a copper ion. The free peptide is C14H24N6O4 at about 340 g/mol, CAS 49557-75-7; the copper complex carries CAS 89030-95-5 and is listed in PubChem as a cation of about 403 g/mol.
Why do different sources give different formulas for GHK-Cu?
Because a metal complex can be written several ways depending on whether the binding nitrogen is counted as deprotonated, what the overall charge is, which counterion balances it, and whether the entry describes one peptide per copper or two. The name does not define the material as tightly as it would for an ordinary peptide.
How does the peptide bind copper?
Through several donor atoms brought into position at once: the terminal amine, the imidazole nitrogen of the histidine, and a backbone nitrogen, holding the metal in a roughly planar arrangement. The geometry of the complex in solution was determined in 1982.
Can mass spectrometry confirm the copper is there?
Yes, and distinctively. Copper has two stable isotopes at roughly 69 and 31 percent natural abundance, so any species containing one copper atom shows a characteristic pair of peaks two mass units apart in that ratio. The free peptide shows no such pattern.
Is an HPLC purity figure enough for GHK-Cu?
No. It reports what share of the detected material was the target sequence, not how much copper is present or whether it is bound in the intended ratio. Copper content is worth reporting as its own figure.
Can the complex come apart during analysis?
It can. Reversed-phase peptide methods usually run at low pH with an acidic additive, and acidic conditions can shift a labile metal complex toward its dissociated form, so a clean peak may correspond to the free tripeptide. For a metal complex the analytical conditions matter more than usual.
References
- Glycyl-L-histidyl-L-lysine compound summary. PubChem, National Library of Medicine (CID 73587).
- Prezatide copper (GHK-Cu) compound summary. PubChem, National Library of Medicine (CID 71587328).
- Freedman, J.H., Pickart, L., Weinstein, B., Mims, W.B., & Peisach, J. (1982). Structure of the glycyl-L-histidyl-L-lysine-copper(II) complex in solution. Biochemistry, 21(19), 4540-4544.
- Harford, C., & Sarkar, B. (1997). Amino terminal Cu(II)- and Ni(II)-binding (ATCUN) motif of proteins and peptides. Accounts of Chemical Research, 30(3), 123-130.