The GHK peptide and GHK-Cu are often used as interchangeable names, but they describe two different materials. GHK is the free tripeptide glycyl-L-histidyl-L-lysine. GHK-Cu is the same tripeptide bound to a copper(II) ion. This article sets out how the two differ in identity, chemistry, appearance and analysis, and why the difference matters when sourcing or documenting research material.
For laboratory research use only. Not for human or veterinary use. See our research use only policy.
At a glance
- Name: GHK (free tripeptide) and GHK-Cu (copper(II) complex)
- Synonyms: Glycyl-L-histidyl-L-lysine; GHK-Cu is also called copper peptide or copper tripeptide-1
- Sequence: Gly-His-Lys (GHK); Gly-His-Lys, copper(II) complex (GHK-Cu)
- Molecular formula: C14H24N6O4 (GHK); C14H22CuN6O4 (GHK-Cu neutral complex, per PubChem)
- Molecular weight: approximately 340.4 g/mol (GHK); approximately 401.9 g/mol (GHK-Cu, per PubChem)
- CAS number: 49557-75-7 (GHK); 89030-95-5 (GHK-Cu)
- Form: Lyophilised powder
- Storage: 2-8°C, dark, upright - do not freeze. Keep sealed until use (Compound Cave GHK-Cu)
For the full background on the copper complex, including history and research overview, see our pillar article on GHK-Cu copper peptide.
The free tripeptide: GHK
GHK is a linear tripeptide of glycine, histidine and lysine. It was first described in human plasma by Pickart and Thaler in 1973, and its sequence was later confirmed as Gly-His-Lys. As a free peptide it is a white to off-white, colourless compound in solid form. It carries three potential metal-binding groups close together near its N-terminus: the free glycine amine, the peptide backbone nitrogen and the histidine imidazole ring.
Those groups give the free peptide a strong affinity for copper(II). In biological fluids and in many experimental media, trace copper is present, which means the free peptide may not stay free for long. Researchers who specifically want to study the metal-free form therefore have to consider the copper content of their buffers and media.
The copper complex: GHK-Cu
When GHK binds copper(II), it forms a compact chelate in which the copper ion is held by the glycine amine nitrogen, a deprotonated amide nitrogen and a histidine imidazole nitrogen. Binding releases protons, which is why the formula of the neutral complex has two fewer hydrogens than the free peptide. This gives a material with a distinct blue to violet colour, a higher molecular weight and different chromatographic behaviour.
Early solution chemistry work, including a 1981 study by Lau and Sarkar in the Biochemical Journal, examined how this complex forms and how it behaves across a range of pH values. A 1988 paper by Maquart and colleagues in FEBS Letters investigated the copper complex in fibroblast cultures and reported changes in collagen synthesis. Much of the subsequent literature focused on the copper-bound form.
Key differences side by side
Identity and registry
The most practical difference is the CAS number. GHK is 49557-75-7 and GHK-Cu is 89030-95-5. Supplier listings occasionally quote the free peptide's number for the copper complex, or the reverse. When checking a label, product page or batch document, confirm that the CAS number matches the form actually described.
Appearance
- GHK: white to off-white powder, colourless in solution.
- GHK-Cu: blue to violet powder, blue in solution.
Colour is a quick first check but it is not proof of identity or purity. A pale or uneven colour in material sold as GHK-Cu could reflect partial complexation, a mixture of forms or moisture uptake, and would justify further analysis.
Molecular weight and mass spectrometry
The free peptide has a monoisotopic mass that gives a protonated ion near 341 m/z in positive-mode ESI-MS. Copper-containing species appear at higher m/z values and show the characteristic copper isotope pattern from copper-63 and copper-65. Under acidic conditions the complex can dissociate, so spectra of GHK-Cu frequently show the free peptide signal as well. Reading these spectra correctly depends on knowing which form was submitted and under what conditions.
Chromatography
Reversed-phase HPLC methods typically use acidic mobile phases, which can strip copper from the complex during the run. Consequently, the HPLC purity figure for GHK-Cu often describes the peptide component rather than the intact complex. Some laboratories add a separate copper determination to characterise the metal content. Our guide on how to read a peptide certificate of analysis explains HPLC and mass spectrometry data in more general terms.
Stability considerations
The free peptide is susceptible to the usual peptide degradation routes, such as hydrolysis and oxidation, and its histidine and lysine side chains are reactive. In the copper complex, the metal can be displaced by stronger chelating agents or reduced by reducing agents, both of which change the material. Practical points on keeping copper complexes in good condition are covered in handling copper peptides in the lab.
Why the distinction matters for research
Published studies have used both forms, and some reported different observations depending on whether copper was present. If an experiment is designed around the copper complex, then free peptide contaminated by variable trace copper is a source of uncontrolled variation. Equally, if the aim is to study the metal-free peptide, inadvertent copper complexation in the medium is a confounder. Recording the exact form, CAS number and source of the material makes work easier to reproduce.
For blended research materials, the same principle applies. Multi-peptide blends that list GHK-Cu as a component contain the copper complex, not the free peptide, which is one reason they are typically blue. We cover these in Glow vs Klow peptide blends.
Which form Compound Cave supplies
Compound Cave supplies the copper complex, GHK-Cu, CAS 89030-95-5, as a lyophilised powder at >99% purity by HPLC. We do not currently list the free tripeptide as a separate product. View GHK-Cu 50mg in the catalogue.
Frequently asked questions
Is GHK the same as GHK-Cu?
No. GHK is the free tripeptide glycyl-histidyl-lysine. GHK-Cu is that tripeptide bound to a copper(II) ion. They have different CAS numbers, formulas, molecular weights and colours.
What is the CAS number of the GHK peptide?
The free GHK tripeptide is CAS 49557-75-7. The copper complex GHK-Cu is CAS 89030-95-5.
Why is GHK-Cu blue?
The blue to violet colour comes from the copper(II) ion held in the peptide's binding site. The free GHK peptide is colourless.
Can free GHK pick up copper on its own?
GHK has a high affinity for copper(II), so in media or fluids that contain trace copper the free peptide may become partly complexed. Researchers studying the metal-free form need to account for this.
Which form does Compound Cave sell?
We supply the copper complex, GHK-Cu, as a lyophilised powder at >99% purity by HPLC, for laboratory research use only.
References
- Pickart L, Thaler MM. Tripeptide in human serum which prolongs survival of normal liver cells and stimulates growth in neoplastic liver. Nature New Biology, 1973.
- Lau SJ, Sarkar B. The interaction of copper(II) and glycyl-L-histidyl-L-lysine, a growth-modulating tripeptide from plasma. Biochemical Journal, 1981.
- Maquart FX, Pickart L, Laurent M, Gillery P, Monboisse JC, Borel JP. Stimulation of collagen synthesis in fibroblast cultures by the tripeptide-copper complex glycyl-L-histidyl-L-lysine-Cu2+. FEBS Letters, 1988.
- Pickart L, Margolina A. Regenerative and protective actions of the GHK-Cu peptide in the light of the new gene data. International Journal of Molecular Sciences, 2018.
- PubChem compound records for glycyl-L-histidyl-L-lysine and its copper(II) complex, National Center for Biotechnology Information.
For laboratory research use only. Not for human or veterinary use. See our research use only policy.