What Is GHK-Cu? Copper-Binding Tripeptide Structure Explained

Key takeaways

• GHK-Cu is the tripeptide glycyl-L-histidyl-L-lysine (Gly-His-Lys, single-letter GHK) bound to a copper(II) ion as a 1:1 coordination complex.
• The free GHK peptide has a molecular formula of C14H24N6O4 and a monoisotopic mass near 340.4 g/mol; the copper-bound GHK-Cu complex adds a Cu(II) center, pushing the formula weight to roughly 401-403 g/mol depending on counter-ions and hydration.
• Copper is coordinated chiefly through the histidine imidazole nitrogen, the deprotonated peptide-bond nitrogen, and the N-terminal amine, with structural studies describing a square-planar geometry around Cu(II).
• GHK-Cu is supplied as a lyophilized powder, reconstituted with bacteriostatic or sterile water, and stored cold and protected from light to preserve the copper-peptide complex.
• Ascend Bio Labs publishes a per-batch Certificate of Analysis with third-party HPLC purity and LC-MS identity data, linked by a unique batch ID on every vial.

GHK-Cu is one of the most frequently discussed copper-peptide complexes in laboratory peptide catalogs, and it is also one of the most commonly misdescribed. It is not simply a short peptide; it is a metal-peptide coordination complex in which a copper(II) ion is held by a three-residue peptide. Understanding GHK-Cu as a research material means understanding both halves of that name: the GHK tripeptide and the copper it carries.

This guide is a structural and handling reference. It describes what the molecule is at the level of sequence, coordination chemistry, molecular weight, and physical form, plus how the lyophilized material is reconstituted and stored in a research setting. It makes no claims about biological activity, outcomes, or use in any organism. GHK-Cu sold by Ascend Bio Labs is a research chemical, labeled for research use only.

The GHK tripeptide: sequence and identity

GHK stands for the three amino acids in the peptide, written N-terminus to C-terminus in single-letter code: glycine (G), histidine (H), and lysine (K). Spelled out, the sequence is glycyl-L-histidyl-L-lysine. It is a tripeptide, meaning a sequence length of exactly three residues joined by two peptide bonds.

The free, copper-free peptide has the molecular formula C14H24N6O4 and a monoisotopic mass of approximately 340.4 g/mol. Each residue contributes a distinct chemical handle: glycine provides the free N-terminal amine, histidine contributes an imidazole side chain, and lysine adds a second basic side-chain amine. As we will see, two of those features, the N-terminal amine and the histidine imidazole, are central to how the peptide binds copper.

For a comparison of how other short research peptides are described by sequence and class, see What Is BPC-157? Peptide Class, Sequence, and Reconstitution and What Is Epithalon? Tetrapeptide Sequence and Molecular Weight.

• Sequence (single-letter): GHK
• Sequence (full): glycyl-L-histidyl-L-lysine
• Sequence length: 3 residues (a tripeptide)
• Free-peptide formula: C14H24N6O4
• Free-peptide monoisotopic mass: ~340.4 g/mol

Why the '-Cu': copper coordination chemistry

The '-Cu' suffix denotes a bound copper(II) ion. GHK-Cu is a coordination complex in which one GHK peptide chelates one Cu(II) center, typically described as a 1:1 stoichiometry. This is the defining structural feature that distinguishes GHK-Cu from the bare GHK peptide; chemically they are different species.

Crystallographic and spectroscopic studies of the complex describe copper held in an approximately square-planar arrangement. The donor atoms reported for the principal binding mode include the imidazole nitrogen of the histidine side chain, the deprotonated amide (peptide-bond) nitrogen between glycine and histidine, and the terminal amine nitrogen of the glycine residue. A water molecule or additional donor can occupy an axial position, and the histidine residue is the linchpin of high-affinity copper binding in this tripeptide.

Because the bound copper is integral to the molecule, GHK-Cu is generally a blue-tinted solid or solution rather than a colorless one, a visual consequence of the d-d electronic transitions of the coordinated Cu(II) ion. The exact color intensity depends on concentration and the salt form.

• Metal center: copper(II), Cu(II)
• Stoichiometry: 1 peptide : 1 copper ion (1:1 complex)
• Principal donor atoms: histidine imidazole N, deprotonated amide N, N-terminal amine N
• Reported geometry: approximately square-planar around Cu(II)
• Characteristic property: blue coloration from coordinated Cu(II)

Molecular weight of the complex

Molecular weight is where GHK and GHK-Cu are most often confused, because the two species have different masses. The free GHK peptide has a formula weight near 340 g/mol. Adding a copper(II) center, while losing protons from the coordinating nitrogens during chelation, produces the GHK-Cu complex.

For the copper-bound complex, the commonly cited formula weight is in the range of roughly 401 to 403 g/mol, often given for the neutral 1:1 complex (a representative formula such as C14H22CuN6O4). The precise figure reported on a Certificate of Analysis can vary slightly depending on whether the value describes the neutral complex, a salt form, or a hydrate, and on how counter-ions are accounted for.

When verifying material, the practical check is identity by mass spectrometry against the expected complex mass. LC-MS confirms that the species present is the copper-bound tripeptide rather than free peptide or a degradation product, which is exactly why batch-level identity testing matters for a metal-peptide complex.

• Free GHK peptide: C14H24N6O4, ~340.4 g/mol
• GHK-Cu complex: representative ~401-403 g/mol (e.g., C14H22CuN6O4 for the neutral 1:1 complex)
• Exact MW depends on salt form, hydration, and counter-ions; defer to the batch COA
• Confirm identity by LC-MS against the expected complex mass

Physical form, reconstitution, and storage

GHK-Cu is supplied as a lyophilized (freeze-dried) powder in a sealed vial. In a research workflow it is reconstituted by adding a measured volume of solvent, typically bacteriostatic water or sterile water for laboratory preparations, and gently swirling rather than vigorously shaking to bring the powder into solution. The volume of solvent chosen sets the concentration of the resulting stock; that calculation is a function of the labeled peptide mass per vial and the desired working concentration.

Because the copper is part of the structure, handling that protects the complex matters more than for a plain peptide. Lyophilized GHK-Cu is generally stored frozen and protected from light; once reconstituted, solutions are kept refrigerated, protected from light, and used within a limited window, as copper-peptide complexes can be sensitive to oxidation, pH, and prolonged warmth. Repeated freeze-thaw cycles of the reconstituted solution are typically minimized.

For a fuller treatment of cold-chain principles that apply to lyophilized peptides and metal-peptide complexes alike, see Peptide Storage and Cold-Chain Handling: A Research Reference.

• Supplied form: lyophilized powder in a sealed vial
• Reconstitution: add bacteriostatic or sterile water; swirl gently, do not shake hard
• Lyophilized storage: frozen, protected from light
• Reconstituted storage: refrigerated, protected from light, freeze-thaw minimized
• Concentration is set by solvent volume relative to labeled peptide mass

Verifying a GHK-Cu batch: COA, HPLC, and LC-MS

For any research peptide, but especially for a metal-peptide complex, the documentation that accompanies the material is what lets a lab trust what is in the vial. A complete Certificate of Analysis for GHK-Cu pairs an HPLC chromatogram (chromatographic purity) with an LC-MS spectrum (molecular identity confirming the copper-bound complex by mass). The batch identifier on the COA should match the identifier on the physical vial.

Ascend Bio Labs publishes a per-batch COA for every compound, with independent third-party HPLC purity testing and LC-MS identity confirmation, and links each report to a unique batch ID printed on the vial. Synthesis, testing, storage, and shipping are US-domestic, with no overseas transshipment, and material ships insulated and tracked. Several other vendors in this space also publish testing documentation; the table below compares verifiable, publicly stated attributes so a buyer can confirm specifics directly with each source.

The neutral rule when comparing vendors is to read each supplier's own COA and verify the batch ID against the vial. Where an attribute is not publicly listed, treat it as something to confirm with the vendor rather than as a deficiency.

Related research notes

• What Is BPC-157? Peptide Class, Sequence, and Reconstitution
• What Is Epithalon? Tetrapeptide Sequence and Molecular Weight
• BPC-157 + TB-500 Blend: What the Combined Vial Contains
• Peptide Storage and Cold-Chain Handling: A Research Reference