GHK-Cu Peptide: Identity, Copper Chemistry and Analysis

The GHK-Cu peptide is the tripeptide glycyl-L-histidyl-L-lysine (Gly-His-Lys, 340.38 g/mol) bound to a copper(II) ion, mainly as a 1:1 complex of about 402 g/mol. Loren Pickart and M. M. Thaler first isolated the tripeptide from human plasma in 1973, and by 1980 the same group had found that it co-purifies with roughly equimolar copper [1]. Since then GHK-Cu has been studied mostly as a coordination compound: by potentiometry, EPR, X-ray crystallography, NMR, calorimetry and computation.

GHK-Cu at a glance

Source: PubChem compound records 73587 and 71587328; references 1 to 5.

Research materials: Vortex supplies GHK-Cu as a lyophilised research reagent: GHK-Cu 50mg and GHK-Cu 100mg. Lab reports: /coa/.

What GHK-Cu is: identity and discovery

GHK is about as small as a metal-binding peptide gets. It has three groups that can hold a metal ion: the free N-terminal amine on glycine, the imidazole side chain of histidine and, at high pH, the epsilon-amino group on the lysine side chain. Two backbone amide nitrogens can also coordinate once they lose a proton. Which of these groups bind copper at a given pH is the core question of the chemistry literature below.

The discovery history is short. Pickart and Thaler reported a tripeptide fraction from human plasma in 1973 and identified it as Gly-His-Lys. In 1980 Pickart and colleagues reported that during isolation the peptide co-purified through several steps with approximately equimolar copper and about one-fifth molar iron [1]. They noted a sequence similarity between GHK and the copper-transport sites of serum albumin and alpha-fetoprotein, where copper sits on a histidine next to a basic residue. In the same paper they reported that the tripeptide readily formed complexes with copper(II) and increased copper uptake into a cultured cell line [1]. That paper also reported the first X-ray structure of the solid copper complex.

The name has drifted over the decades. The 1980 and 1982 papers abbreviate the peptide GHL, from its three-letter initials. Later work uses the one-letter code, GHK, and the copper complex is written GHK-Cu or Cu(II)-GHK. All of these names describe the same sequence. The “Cu” suffix describes a complex, not a covalent part of the peptide, which matters for how the material is analysed.

Copper coordination chemistry of GHK-Cu

Species in solution and their pH dependence

Lau and Sarkar studied copper(II) and GHK in 1981 by potentiometry and visible-absorption spectrophotometry at 25 °C in 0.15 M sodium chloride [2]. Across pH 3.5 to 10.6 they found several copper-peptide species in solution, not one fixed complex. When L-histidine was also present, ternary complexes formed in large amounts. The lysine epsilon-amino group raised the stability constants compared with the shorter peptides Gly-His and Gly-His-Gly [2].

Freedman and colleagues followed in 1982 with optical, EPR and electron spin-echo spectroscopy [3]. At neutral pH they found a mononuclear 1:1 copper complex with two or three equatorial nitrogen donors, one of them from the histidine imidazole ring. As the pH changed they saw three optical transitions, with apparent pK values of 3.6, 9.2 and 11.4. Copper binds at the lowest of these, forming the species present at neutral pH. At higher pH the copper environment changed while the imidazole stayed bound. They also concluded that the polymeric solid-state structure, with oxygen-bridged copper pairs, does not exist in solution [3].

Conato and colleagues extended this work in 2001 with potentiometry, solution calorimetry, UV-visible spectrophotometry, circular dichroism and EPR [4]. They compared GHK with two synthetic analogues in which histidine was replaced by a non-natural amino acid. All three ligands formed complexes of several stoichiometries, including binuclear species. The lysine side-chain amine joined the copper site only at alkaline pH. At neutral pH it stayed protonated and free [4].

Structure in the solid state and in solution

Hureau and colleagues solved X-ray structures and used EPR, HYSCORE, X-ray absorption and NMR spectroscopy to compare the solid and solution forms [5]. In the crystal, Cu(II)-GHK is a dimer. In solution it is a monomer in which copper is held by three nitrogen atoms: the terminal amine, a deprotonated amide nitrogen and the histidine imidazole. The fourth equatorial position is taken by a labile oxygen donor, a carboxylate oxygen in the crystal. They also studied ternary complexes with glycine and histidine at that fourth position [5].

Two further results from that study are useful to anyone handling the material. Copper exchanged quickly between GHK molecules, which the authors attributed to a transient bis-peptide species, [Cu(GHK)2]. In cyclic voltammetry and ascorbate-oxidation measurements, the complex was inert under moderate redox conditions, but it could be reduced to copper(I) at around −0.62 V (versus AgCl/Ag), with release of the metal [5].

A computational study in 2020 reached a consistent picture [6]. Alshammari and Platts combined ligand-field molecular mechanics, density functional theory and semi-empirical methods. Over a 100 ps molecular-dynamics run, four equatorial bonds in a 3N1O arrangement stayed stable, while a fifth, apical bond from the C-terminal carboxylate was more fluxional. An automated conformer search predicted the correct copper-binding position starting from separated peptide, copper and water [6].

Competition with albumin and ternary complexes

GHK shares plasma with serum albumin, which also binds copper at its N-terminus. In equilibrium-dialysis experiments at pH 7.5 and 6 °C, Lau and Sarkar found that GHK competed with albumin for copper. At equal concentrations of albumin and peptide, about 42% of the copper ended up on the peptide [2]. In 2021, Bossak-Ahmad and colleagues characterised ternary complexes in which a Cu(GHK) unit is bound to a histidine imidazole of human serum albumin [7]. They identified His3 as one site, with a conditional binding constant of 2,900 M^-1 at pH 7.4, and a second site of 1,700 M^-1, probably His128 or His510 [7].

Source: references 1 to 7. All are chemistry or structural studies.

GHK as a tool in protein crystallography

The tight, well-defined copper site of GHK has found a use that has nothing to do with the free peptide. In 2020, Mehr and colleagues fused the GHK sequence to the N-terminus of two test proteins, a GFP variant and an MBP fusion, and used the bound copper to help solve their crystal structures [8]. The tag promoted crystallisation. In the crystals, residues from neighbouring molecules (histidine, aspartate, or histidine and proline) completed a square-pyramidal copper site. The copper atom also provided an anomalous signal for phasing, and structures could be solved by copper SAD phasing even at a very low Bijvoet ratio or after significant radiation damage [8].

This is a useful independent check on the solution chemistry. It shows the same three-nitrogen copper site, with open positions filled by whatever donors are nearby, in a setting where the peptide is part of a larger protein.

What the GHK-Cu literature looks like

A PubMed search on 21 October 2026 returned about 300 records that mention GHK or glycyl-L-histidyl-L-lysine in the title or abstract. The abbreviation also matches some unrelated uses, so the true figure is somewhat lower. The record falls into four broad groups: coordination chemistry and structure (the papers summarised above), cell-culture pharmacology, rodent pharmacology, and reviews. Eleven of the records list the discoverer, Loren Pickart, as an author, and several of the reviews come from that group.

No controlled human studies of isolated GHK-Cu have been published. The next section reports a set of cell-culture measurements, each in the model the authors named. This article does not summarise the rodent pharmacology. Its main scope is what the molecule is, how it holds copper and how a lot is verified.

What cell and molecular studies of GHK-Cu have measured

The cell-culture papers on GHK-Cu report molecular measurements: where copper went, and how much of a matrix molecule or an enzyme cultured cells made. Each finding below is stated in the model the authors used. These are measurements in cell culture. They do not describe outcomes in an organism.

Copper delivery to cultured cells

The 1980 paper that linked GHK to copper reported that the tripeptide readily formed complexes with copper(II) and raised the uptake of copper into a cultured cell line [1]. A 1989 ESR study by Antholine, Petering and Pickart gave a more complicated picture [12]. When CuGHK was added to Ehrlich cells, a mouse cell line, no ESR-detectable copper adducts formed, and the authors read this as consistent with poor uptake of the intact complex. A ternary CuGHK-histidine adduct was not stable in the presence of the cells, and the authors argued that the copper ended up in a Cu(His)2 complex [12]. Which copper species actually crosses the cell membrane is not settled by these two papers.

Collagen and glycosaminoglycan synthesis in cultured fibroblasts

In 1988, Maquart and colleagues measured collagen synthesis in fibroblast cultures exposed to GHK-Cu [13]. They reported higher collagen synthesis than in control cultures, and the change was independent of any change in cell number. They also noted that the GHK sequence occurs within the alpha 2(I) chain of type I collagen [13].

Wegrowski and colleagues followed in 1992 with normal human fibroblasts in culture [14]. They labelled newly made glycosaminoglycans (GAGs) with tritiated glucosamine and ³⁵S-sulfate, then measured the radioactivity of the isolated GAGs. With GHK-Cu present, synthesis of total GAGs was higher, both for GAGs secreted into the medium and for those associated with the cell layer. The response was biphasic: it peaked in a narrow concentration range and returned towards control levels at higher concentrations. Electrophoresis showed the largest changes in extracellular dermatan sulfate and cell-layer heparan sulfate. Hyaluronic acid synthesis did not change [14].

Metalloproteinase expression in cultured fibroblasts

In 2000, Siméon and colleagues measured matrix metalloproteinase-2 (MMP-2) in fibroblast cultures [15]. With GHK-Cu present, MMP-2 levels in the conditioned medium were higher, and so was MMP-2 mRNA. Copper ions alone reproduced the change, but the GHK peptide without copper did not. The same cultures also secreted more of two tissue inhibitors of metalloproteinases, TIMP-1 and TIMP-2 [15]. That result ties the measured response to the copper in the complex rather than to the peptide chain alone, which links it back to the coordination chemistry above.

Source: abstracts of references 1 and 12 to 15, checked on PubMed. All are cell-culture or cell-suspension studies.

Analytical verification of GHK-Cu

GHK-Cu raises analytical questions that a plain peptide does not. The material is a metal complex, so a lab may want to know three things: is the peptide correct, is it pure, and how much of the copper is actually bound.

Identity by mass spectrometry

Electrospray ionisation is the standard way to bring peptides into a mass spectrometer intact [10]. LC-MS confirms identity by matching the observed mass to the expected mass. The free GHK peptide has a monoisotopic mass of 340.186 Da, so its singly protonated ion appears near m/z 341.19. Acidic LC mobile phases protonate the histidine and the terminal amine, which can strip copper from the peptide during the run. A spectrum may therefore show the free peptide ion, a copper-containing ion, or both. The presence of the free-peptide ion alone does not mean the vial contained uncomplexed peptide.

When a copper-containing ion survives, it has a distinctive signature. Copper has two stable isotopes, ⁶³Cu and ⁶⁵Cu, in a natural ratio of about 69 to 31. The singly charged complex [Cu(GHK−H)]⁺ therefore appears as a pair of peaks near m/z 402.11 and 404.11, roughly 2.2 to 1 in height. That pattern is a quick confirmation that the ion carries copper rather than a coincidental contaminant of similar mass.

Purity by HPLC-UV

Reverse-phase HPLC with UV detection separates the main peptide from synthesis-related impurities such as deletion sequences and protecting-group adducts. Column chemistry and organic solvent both shift peptide selectivity, so the method matters [9]. GHK is small and very polar, so on a standard C18 column it elutes early, close to the solvent front, where integration is least reliable. Purity is reported as the main peak area as a percentage of all detected peak area. It is a relative figure. It does not measure water, counter-ions or copper content.

Free copper versus complexed copper, and colour

Copper(II) complexes of GHK absorb visible light [2], which is why the lyophilised material is blue to violet-blue. Colour is a quick visual check, but it is not a quantitative test. A pale or greenish cake can point to a different copper species or excess free copper salt, but only a measurement can confirm that. Labs that need the copper-to-peptide ratio use total-copper analysis, such as ICP-OES or ICP-MS, alongside a peptide assay. Separating bound from unbound copper needs an additional method, such as chelator competition or spectrophotometry. Because copper exchanges quickly between GHK molecules [5], any such measurement describes an equilibrium at the conditions used, not a fixed property of the solid.

Net content

Net content is the measured amount of material in the vial, separate from purity. For a copper complex it includes the copper and any counter-ions, not only the peptide chain. The molar mass used to convert between peptide and complex should be stated, because 340 g/mol and 403 g/mol give answers that differ by about 18%.

Stability chemistry of lyophilised GHK-Cu

Peptides in the solid state are not inert. A review of solid-state peptide chemistry lists the main reactions as deamidation, peptide-bond cleavage, oxidation, the Maillard reaction, beta-elimination and dimerisation or aggregation, with temperature, moisture and the physical state of the solid as the main drivers [11]. GHK has no asparagine or glutamine, so deamidation is not a concern. Its two free amines (the N-terminus and the lysine side chain) can take part in Maillard chemistry if reducing sugars are present. Its histidine is the most oxidation-prone residue, and copper is a redox-active metal. The 2011 voltammetry work found the complex inert under moderate redox conditions [5], which is consistent with the material being handled routinely as a solid.

Practically, that means the same conditions used for other freeze-dried peptides: cold, dry and away from light, with moisture as the main variable to control. The degradation chemistry behind those conditions is covered in storing lyophilised peptides.

Checking a lot of GHK-Cu

The published Vortex report for GHK-Cu 50 mg covers lot VR01-GHK. It was tested for Vortex Research by Freedom Diagnostics and reported on 06/20/2026. The report lists three assays:

• Purity (HPLC-UV): 99.85%
• Identity (LC-MS): confirmed
• Net content: 54.92 mg in a vial labelled 50 mg

This report does not list a separate copper assay, so this article makes no claim about the copper-to-peptide ratio for that lot. The /coa/ page also shows a report for the 100 mg size. That report was issued to a wholesale partner facility for its batch, not commissioned by Vortex, and the page labels it as a partner-facility report. Each report on the page has a verification link to the testing lab. For a walk-through of how to read these documents, see how to read a peptide COA. For criteria that apply across suppliers, see how to evaluate a research peptide supplier.

Open questions in GHK-Cu chemistry

• Which species is in the vial? GHK-Cu is an equilibrium of several species that shift with pH and competing ligands [2, 3, 4]. The solid is a dimer in the crystal [5], but the form in an amorphous lyophilised cake has not been characterised.
• How much copper is free? Commercial certificates rarely report bound and unbound copper separately, and fast exchange [5] makes the answer condition-dependent.
• What is the counter-ion? The complex is a cation, so the solid carries counter-ions. Their identity and amount change the net-content arithmetic.

GHK-Cu is also one component of the GLOW and KLOW blends, whose composition is covered in GLOW vs KLOW blend composition. For an identity-first overview of another catalogue compound, see the BPC-157 research overview.

Frequently asked questions

What is GHK-Cu?

GHK-Cu is the copper(II) complex of the tripeptide glycyl-L-histidyl-L-lysine. The free peptide has a molar mass of 340.38 g/mol, and the 1:1 copper complex cation is about 402.9 g/mol. Pickart and Thaler first isolated the tripeptide from human plasma in 1973.

How does GHK bind copper?

At neutral pH, GHK holds copper(II) as a mononuclear 1:1 complex through three nitrogen atoms: the terminal amine, a deprotonated amide nitrogen and the histidine imidazole. A labile oxygen donor fills the fourth position. In the crystal the complex is a dimer.

Why is GHK-Cu blue?

Copper(II) bound to the peptide’s nitrogen atoms absorbs visible light, so the complex appears blue to violet-blue. Colour is a useful first check, but it does not quantify copper or purity. Those need instrumental tests.

What have cell studies of GHK-Cu measured?

Cell-culture papers report molecular measurements. In fibroblast cultures, researchers reported higher collagen synthesis, higher glycosaminoglycan synthesis and higher MMP-2 protein and mRNA with GHK-Cu present than in control cultures. Copper ions alone reproduced the MMP-2 change. On copper handling, one paper reported higher copper uptake into a cultured cell line, while an ESR study found little uptake of the intact complex.

What does the Vortex GHK-Cu report show?

The report for lot VR01-GHK (50 mg), tested for Vortex by Freedom Diagnostics and reported on 06/20/2026, lists purity of 99.85% by HPLC-UV, identity confirmed by LC-MS and net content of 54.92 mg. It does not list a separate copper assay. The full report is on the /coa/ page.

About this article: Written by the Vortex Research Editorial Team. Sources were chosen from peer-reviewed papers indexed in PubMed, with priority given to primary chemistry and structural studies and to cell-culture papers that state their model and measurement. Each PMID was checked against PubMed for title, journal and year, and each sentence was matched to the paper’s abstract. Identity data come from PubChem records, quoted without linking. Publication counts come from a PubMed search run on 21 October 2026.

Research materials: GHK-Cu 50mg and GHK-Cu 100mg are supplied as lyophilised research reagents. Published lab reports are at /coa/.

References

1. Pickart L, Freedman JH, Loker WJ, et al. Growth-modulating plasma tripeptide may function by facilitating copper uptake into cells. Nature. 1980;288(5792):715-717. PMID: 7453802. doi:10.1038/288715a0
2. Lau SJ, Sarkar B. The interaction of copper(II) and glycyl-L-histidyl-L-lysine, a growth-modulating tripeptide from plasma. Biochem J. 1981;199(3):649-656. PMID: 7340824. doi:10.1042/bj1990649
3. Freedman JH, Pickart L, Weinstein B, Mims WB, Peisach J. Structure of the glycyl-L-histidyl-L-lysine-copper(II) complex in solution. Biochemistry. 1982;21(19):4540-4544. PMID: 6291585. doi:10.1021/bi00262a004
4. Conato C, Gavioli R, Guerrini R, et al. Copper complexes of glycyl-histidyl-lysine and two of its synthetic analogues: chemical behaviour and biological activity. Biochim Biophys Acta. 2001;1526(2):199-210. PMID: 11325542. doi:10.1016/s0304-4165(01)00127-1
5. Hureau C, Eury H, Guillot R, et al. X-ray and solution structures of Cu(II) GHK and Cu(II) DAHK complexes: influence on their redox properties. Chemistry. 2011;17(36):10151-10160. PMID: 21780203. doi:10.1002/chem.201100751
6. Alshammari N, Platts JA. Theoretical study of copper binding to GHK peptide. Comput Biol Chem. 2020;86:107265. PMID: 32371360. doi:10.1016/j.compbiolchem.2020.107265
7. Bossak-Ahmad K, Bal W, Frączyk T, Drew SC. Ternary Cu(2+) complexes of human serum albumin and glycyl-l-histidyl-l-lysine. Inorg Chem. 2021;60(22):16927-16931. PMID: 34730942. doi:10.1021/acs.inorgchem.1c03084
8. Mehr A, Henneberg F, Chari A, Görlich D, Huyton T. The copper(II)-binding tripeptide GHK, a valuable crystallization and phasing tag for macromolecular crystallography. Acta Crystallogr D Struct Biol. 2020;76(Pt 12):1222-1232. PMID: 33263328. doi:10.1107/S2059798320013741
9. Mant CT, Cepeniene D, Hodges RS. Reversed-phase HPLC of peptides: assessing column and solvent selectivity on standard, polar-embedded and polar endcapped columns. J Sep Sci. 2010;33(19):3005-3021. PMID: 21038458. doi:10.1002/jssc.201000518
10. Fenn JB, Mann M, Meng CK, Wong SF, Whitehouse CM. Electrospray ionization for mass spectrometry of large biomolecules. Science. 1989;246(4926):64-71. PMID: 2675315. doi:10.1126/science.2675315
11. Lai MC, Topp EM. Solid-state chemical stability of proteins and peptides. J Pharm Sci. 1999;88(5):489-500. PMID: 10229638. doi:10.1021/js980374e
12. Antholine WE, Petering DH, Pickart L. ESR studies of the interaction of copper(II)GHK, histidine, and Ehrlich cells. J Inorg Biochem. 1989;35(3):215-224. PMID: 2542448. doi:10.1016/0162-0134(89)84011-5
13. 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 Lett. 1988;238(2):343-346. PMID: 3169264. doi:10.1016/0014-5793(88)80509-x
14. Wegrowski Y, Maquart FX, Borel JP. Stimulation of sulfated glycosaminoglycan synthesis by the tripeptide-copper complex glycyl-L-histidyl-L-lysine-Cu2+. Life Sci. 1992;51(13):1049-1056. PMID: 1522753. doi:10.1016/0024-3205(92)90504-i
15. Siméon A, Emonard H, Hornebeck W, Maquart FX. The tripeptide-copper complex glycyl-L-histidyl-L-lysine-Cu2+ stimulates matrix metalloproteinase-2 expression by fibroblast cultures. Life Sci. 2000;67(18):2257-2265. PMID: 11045606. doi:10.1016/s0024-3205(00)00803-1

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