GHK-Cu: The Copper-Binding Tripeptide Explained
Research Use Only. This article is written for laboratory and research professionals. The compounds discussed are supplied strictly for in-vitro laboratory research. They are not drugs, dietary supplements, or foods. They are not for human or veterinary use, and not for diagnostic or therapeutic use. Nothing here is medical, legal, or regulatory advice.
The short answer
GHK-Cu is the copper(II) complex of a three-residue peptide, glycyl-L-histidyl-L-lysine. The peptide itself was identified in human plasma in 1973. Its histidine side chain, together with the N-terminal amine and one backbone amide nitrogen, forms a nitrogen-rich site that holds a single Cu(II) ion with high affinity. The published literature studies the complex in cell culture and animal models, principally around collagen and glycosaminoglycan synthesis pathways, metalloproteinase and TIMP expression, redox behaviour, and copper transfer between binding partners. Those are laboratory observations in defined systems, not statements about people.
This article covers structure and mechanism. It is not a guide to use of any kind.
What GHK-Cu is, chemically
The sequence
The peptide is written Gly-His-Lys, or GHK in single-letter code, and read from the free amino terminus to the free carboxyl terminus. Three residues, two peptide bonds. In full stereochemical notation it is glycyl-L-histidyl-L-lysine, which specifies that both chiral residues are the L enantiomers found in ribosomally synthesised protein. Catalogues and search queries render the name several ways: GHK-Cu, GHK Cu, GHK Cu peptide, GHK Cu peptides, copper-GHK, copper tripeptide-1. All name the same complex, and the hyphen is typographic rather than chemical.
Each residue contributes something different:
- Glycine is the smallest amino acid, with a hydrogen atom for a side chain. Sitting at position one, it leaves the N-terminal amine sterically unhindered and free to coordinate a metal ion.
- Histidine carries an imidazole ring. Imidazole is the standard metal-binding side chain in biology and the reason this particular sequence binds copper rather than simply passing it by.
- Lysine carries a four-carbon chain ending in a primary amine. At physiological pH that amine is protonated, so it does not compete for the copper. It gives the molecule a net positive charge instead.
Molecular formula and mass
Free GHK is C₁₄H₂₄N₆O₄, with an average molecular mass of 340.38 g/mol, catalogued as PubChem CID 73587. The 1:1 copper complex is catalogued separately: PubChem lists the copper species as C₁₄H₂₃CuN₆O₄⁺ at 402.92 g/mol, with CAS number 89030-95-5 and the INCI cosmetic name copper tripeptide-1.
Several database entries exist for one molecule, and the reason is protonation state. Copper binding displaces protons from the ligand, so the formula and the net charge you write down depend on which species you are describing and at what pH. A second entry, C₁₄H₂₁CuN₆O₄⁻ at 400.90 g/mol, describes the doubly deprotonated form. Supplied material is usually a salt, commonly an acetate, adding counterion mass the peptide formula excludes. This is why net peptide content, not gross vial weight, is the meaningful quantity on a certificate of analysis.
Why histidine is the residue that matters
Copper(II) is a borderline Lewis acid. It prefers nitrogen and oxygen donors, and among the amino acid side chains the imidazole of histidine is the strongest common nitrogen donor. Imidazole has two ring nitrogens: one carries a proton, the other has a lone pair available for coordination. Around neutral pH that second nitrogen is largely deprotonated and available.
Position matters as much as identity. Histidine at position two of a peptide creates the classic ATCUN motif (amino-terminal Cu(II) and Ni(II) binding site), the same arrangement found at the N-terminus of human serum albumin, whose sequence begins Asp-Ala-His. A free alpha-amino group with a histidine two residues along produces a chelate geometry that binds Cu(II) far more tightly than the individual donors would predict. Move the histidine, block the N-terminus, or replace the imidazole, and the site is degraded or lost.
Two consequences follow. First, the sequence is not interchangeable with other tripeptides: Maquart and colleagues used L-glutamyl-L-histidyl-L-proline as a negative control in animal work and saw no comparable effect. Second, chemical modification at the N-terminus, including the palmitoyl conjugation used in cosmetic derivatives, changes the copper chemistry rather than leaving it intact.
The copper(II) coordination site
The solution structure was resolved by spectroscopy rather than by crystallography. Freedman and colleagues applied optical spectroscopy, electron paramagnetic resonance and electron spin-echo envelope modulation to the complex, and published the analysis in 1982. Their findings: at neutral pH the peptide forms a mononuclear 1:1 Cu(II) complex whose EPR spectrum matches equatorial coordination by two or three nitrogen atoms, and spin-echo data place one of those nitrogens in the histidyl imidazole ring.
The assignment usually drawn from this is a three-nitrogen equatorial set:
- the N-terminal amine nitrogen of glycine,
- the deprotonated amide nitrogen of the glycine-histidine peptide bond,
- an imidazole nitrogen from the histidine side chain.
Deprotonating a backbone amide nitrogen is the key step and it is pH dependent. The same study's optical titration found apparent pK values near 3.6, 9.2 and 11.4, with the lowest of those marking formation of the species that predominates at physiological pH. Below that transition the complex is not assembled; well above neutral pH the geometry rearranges, though the bound imidazole is retained.
One further detail is easy to miss. An earlier X-ray structure of crystalline material described a polymeric arrangement with oxygen-bridged copper pairs. The 1982 solution work showed that this polymeric form does not exist in solution. Solid-state and solution structure differ here, which matters when interpreting measurements made on dry powder.
Free GHK and the copper complex are not the same reagent
Papers and vendors use both terms loosely. The distinction is real.
Free GHK is the apopeptide: white lyophilized powder, no coordinated metal, and readily able to pick up copper from the environment, including from copper contaminating buffers and glassware. GHK-Cu is the preformed complex, usually blue to blue-violet, in which the metal is already bound.
In cell culture the two are not equivalent inputs, but neither are they cleanly separable, because medium and serum contain copper and competing ligands. Siméon and colleagues reported that the increase in matrix metalloproteinase-2 they measured in fibroblast cultures was reproduced by copper ions but not by the tripeptide alone, which points to copper as the proximate signal in that assay. Other groups have reported effects of copper-free GHK in keratinocyte and skin-equivalent models. Both results can hold: the readouts are different, the models are different, and whether a given experiment is testing the ligand, the metal, or the complex is a question the experimental design has to answer explicitly.
For anyone designing work with either form, a copper salt arm, an apopeptide arm and a chelator arm answer questions a single GHK-Cu arm cannot.
Discovery, plasma occurrence, and the reported age-related decline
1973, and how the peptide was found
GHK was not designed. It was isolated from human plasma by Loren Pickart, working with Marion Thaler, and reported in Nature New Biology in 1973 under the title Tripeptide in human serum which prolongs survival of normal liver cells and stimulates growth in neoplastic liver.
The route to it was activity-guided fractionation, the standard approach of the period. Plasma was separated into fractions, each was tested in a tissue-culture assay, and the active ones were carried forward and separated again until the activity concentrated into a chemically definable species. It travelled with the albumin-containing material. Chromatography and sequencing then resolved it to three residues. Structure came last, after the biology had indicated something was there.
Reported concentrations and the decline with age
The figure quoted almost everywhere traces to Pickart's own review work. A 2015 review in BioMed Research International states that plasma GHK is around 200 ng/mL, roughly 10⁻⁷ M, at age 20, declining to about 80 ng/mL by age 60, and that the peptide is also detectable in saliva and urine. Other work describes its presence in cerebrospinal fluid.
Treat that number as a reported literature value rather than a settled constant. It is a single lineage of measurement, repeated across reviews by the same author group, and quantifying a small peptide in plasma against a background of abundant proteins is not trivial analytically. It is worth citing accurately and worth not over-interpreting.
Sequence sources in the extracellular matrix
Free plasma peptide is not the only proposed source. The GHK triplet occurs within the alpha-2 chain of type I collagen, which led Maquart and colleagues to propose in 1988 that proteases could liberate it locally at a site of tissue damage.
A second source is better characterised. Lane and colleagues showed that proteolysis of SPARC, a matrix-associated glycoprotein, yields KGHK, GHK and longer peptides containing those sequences, and that peptides from the cationic 113 to 130 region of SPARC stimulated endothelial cord formation in vitro. Notably, in that system the activity was sequence specific and did not require prior incubation with Cu(II), so the peptide and the metal complex are not always doing the same job.
What the in-vitro and animal literature examines
Four domains account for most of the published work. The companion literature review covers models and measured endpoints in detail; the summary here is mechanistic.
Collagen and glycosaminoglycan synthesis pathways. The 1988 FEBS Letters study measured collagen synthesis in fibroblast cultures and reported a response beginning between 10⁻¹² and 10⁻¹¹ M and peaking near 10⁻⁹ M, with no accompanying change in cell number. Later work in rats measured glycosaminoglycan composition and the messenger RNA levels of the small proteoglycans decorin and biglycan.
Metalloproteinase modulation. The same Reims group reported that GHK-Cu raised MMP-2 protein and messenger RNA in dermal fibroblast cultures while also raising secretion of the tissue inhibitors TIMP-1 and TIMP-2. That combination is worth noting: an increase in a matrix-degrading enzyme alongside an increase in its inhibitors describes turnover, not simple synthesis.
Redox and antioxidant behaviour. Copper is redox active, which cuts both ways. Free Cu(II)/Cu(I) cycling generates reactive oxygen species; chelated copper behaves differently depending on the ligand and the geometry. Work by Miller and colleagues examined the chelated complex in a ferritin-dependent lipid peroxidation system, the type of cell-free assay used to characterise how a ligand alters the metal's reactivity.
Gene expression profiling. More recent analyses use public transcriptional profiling datasets, notably the Broad Institute's Connectivity Map, to compare the expression signature associated with GHK against those of other small molecules. Reviews from Pickart's group report effects across thousands of transcripts. These are computational comparisons over existing signature databases, not fresh experiments.
Why it is studied as a copper delivery vehicle
This is the mechanistic thread tying the rest together. Copper in plasma is not free. Most is bound to ceruloplasmin, with a smaller exchangeable pool associated with albumin and low-molecular-weight ligands; the NIH Office of Dietary Supplements summary of copper describes that distribution. Ionic copper is reactive and tightly controlled, so any process needing copper needs a way to move it without releasing it.
GHK's affinity places it in an interesting position. Reviews cite an association constant for GHK-Cu (pK near 16.4) marginally above that reported for the albumin site (pK near 16.2), which would allow exchange in either direction under physiological conditions rather than one-way sequestration. A ligand that binds slightly more tightly than the main carrier can accept the metal and still release it to a stronger acceptor downstream.
That reasoning is old. Pickart's 1980 Nature paper was titled Growth-modulating plasma tripeptide may function by facilitating copper uptake into cells, which states the hypothesis directly. Much later work is best read as testing it: if a nitrogen-coordinated, neutral-to-cationic copper complex crosses membranes or hands copper to cellular acceptors more readily than the ionic metal does, then several downstream observations follow without the peptide needing an independent receptor.
What the structure does not tell you
Structural characterisation defines what a molecule is and what it can bind. It does not establish what happens in an intact organism, and that gap is where most overstatement about this compound lives.
Concretely: the plasma affinity argument does not establish cellular uptake; a fibroblast culture result does not establish a tissue result; a rodent chamber result does not establish a human result; and a signature comparison does not establish a phenotype. Each step is a separate empirical question. The published record on GHK-Cu is unusually deep on chemistry and unusually thin on controlled outcomes, and content that blurs the two is describing a different compound from the one in the papers.
Handling GHK-Cu as a laboratory material
The chemistry sets the handling requirements. The complex assembles through pH-dependent amide deprotonation, so the buffer determines which species you have. Copper is redox active, so oxidising conditions and trace metals matter. Strong chelators such as EDTA compete for it directly. Lyophilized powder stored cold, dry and dark is far more stable than the same material in solution.
Documentation carries the rest: identity by mass spectrometry, purity by reversed-phase HPLC, copper content by an elemental method, counterion identified, net peptide content stated, all tied to a specific lot. Material without lot-level documentation is not a characterised reagent. Research-grade GHK-Cu is a different category of material from a formulated consumer product containing the same INCI ingredient, a distinction covered on the GHK-Cu product page.
Working with this material
The certificate of analysis for GHK-Cu, from Horizon Analytical, is on the product page and on Lab results. Our own lot records appear at the lot lookup as lots are released. Supplied for laboratory research use only. Not for human or veterinary use.
Compliance notice. Nothing in this article should be read as guidance for administering any compound to a human or animal subject. "Research Use Only" describes the conditions under which a material is supplied; it is not a determination of legal status and confers no exemption from the Federal Food, Drug, and Cosmetic Act. Researchers are responsible for compliance with all applicable federal, state, and institutional requirements, and for obtaining any approvals their work requires.
Frequently asked questions
What is the GHK-Cu peptide?
GHK-Cu is the copper(II) complex of the tripeptide glycyl-L-histidyl-L-lysine. The free peptide has the formula C₁₄H₂₄N₆O₄ and a molecular mass of 340.38 g/mol; the 1:1 copper species is catalogued at 402.92 g/mol. It was isolated from human plasma in 1973 and is studied in laboratory models as a copper-binding ligand.
What does GHK-Cu do at the molecular level?
It coordinates a single Cu(II) ion through a nitrogen-rich site formed by the N-terminal amine, a deprotonated backbone amide nitrogen, and the histidine imidazole. In cell and animal models the published literature examines its association with collagen and glycosaminoglycan synthesis pathways, metalloproteinase and TIMP expression, and copper transfer between ligands. Those are model-system observations.
What is the difference between GHK and GHK-Cu?
GHK is the free tripeptide with no metal bound. GHK-Cu is the preformed 1:1 copper(II) complex. They differ in colour, charge, formula and reactivity, and in cell culture they are not equivalent inputs, though media components make the separation imperfect because copper and competing ligands are already present.
Why does copper bind to the histidine residue?
Copper(II) prefers nitrogen donors, and the imidazole ring of histidine is the strongest common nitrogen donor among amino acid side chains. Histidine at position two, combined with a free N-terminal amine, creates the amino-terminal copper binding arrangement also present in human serum albumin, which produces much higher affinity than the individual donors would give.
Where does GHK come from in the body?
It was first isolated from human plasma. The same sequence occurs within the alpha-2 chain of type I collagen and within the matrix protein SPARC, and proteolysis of SPARC has been shown to release GHK-containing fragments. It has also been reported in saliva, urine and cerebrospinal fluid.
Does GHK really decline with age?
A frequently cited review reports plasma GHK at roughly 200 ng/mL at age 20 and about 80 ng/mL by age 60. That figure comes from a single lineage of measurement rather than multiple independent groups, so it is best cited as a reported literature value rather than a fixed constant.
Is GHK-Cu the same thing as a copper peptide serum?
No. Copper tripeptide-1 is the INCI name used when the same molecule appears as a cosmetic ingredient, but a formulated consumer product and a lyophilized research reagent differ in concentration, matrix, stability, documentation and regulatory category. The two are not interchangeable materials, and the differences between cosmetic formulations and research-grade copper peptide are set out separately.
Primary sources
The remaining literature cited above, for direct verification:
- Tripeptide in human serum which prolongs survival of normal liver cells and stimulates growth in neoplastic liver: https://pubmed.ncbi.nlm.nih.gov/4349963/
- 2015 review in BioMed Research International: https://pmc.ncbi.nlm.nih.gov/articles/PMC4508379/
- propose in 1988 that proteases could liberate it locally: https://pubmed.ncbi.nlm.nih.gov/3169264/
- yields KGHK, GHK and longer peptides containing those sequences: https://pmc.ncbi.nlm.nih.gov/articles/PMC2120067/
- NIH Office of Dietary Supplements summary of copper: https://ods.od.nih.gov/factsheets/Copper-HealthProfessional/
- Growth-modulating plasma tripeptide may function by facilitating copper uptake into cells: https://www.nature.com/articles/288715a0
