GHK-Cu and AHK-Cu sit next to each other in most copper-peptide catalogues, ours included, and they look like variations on a theme. Chemically they almost are: the two tripeptides differ by a single methyl group. In the published record, though, they are not close at all. One has a randomised controlled trial in people behind it. The other has, as far as we can find, five records in the entire Europe PMC database and a single primary study.
This article compares them on what is actually published, sets out the structural difference and how an analytical report distinguishes them, and is explicit about two places where the popular account of GHK-Cu is not supported by the papers it cites.
The short answer
- They differ by one methyl group. GHK is glycyl-L-histidyl-L-lysine; AHK is alanyl-L-histidyl-L-lysine. Alanine carries one extra CH2, so AHK is 14.0157 Da heavier.
- GHK was first reported in 1973 by Pickart and Thaler in Nature New Biology, as a growth-modulating tripeptide in human serum.
- GHK-Cu has one genuine human randomised trial, in diabetic neuropathic ulcers, published in 1994 — and it tested a finished formulated wound gel, not a research-grade vial.
- AHK-Cu has no human data we could locate, and one primary study: an ex-vivo human hair-follicle and cultured dermal-papilla-cell experiment from 2007.
- No head-to-head comparison exists. We could find no published study comparing GHK-Cu and AHK-Cu directly. Any ranking of one against the other is inference.
- The copper chemistry is not one tidy complex. A 2001 study using five physical methods found multiple stoichiometries and evidence for binuclear species.
- The GHK-Cu antioxidant-gene story does not hold up. The Nrf2 claim traces to a single mislabelled table row in a review written by a copper-peptide company’s own staff.
- Intact mass separates GHK from AHK but not from a sequence isomer. Lys-His-Gly has the identical formula and mass.
Two copper-binding tripeptides
GHK · Gly-His-Lys · AHK · Ala-His-Lys
- GHK formula and mass
- C14H24N6O4; monoisotopic 340.1859, average 340.384
- AHK formula and mass
- C15H26N6O4; monoisotopic 354.20155, average 354.411; CAS 126828-32-8
- Structural difference
- Residue 1 only: glycine against alanine, a single CH2 — 14.0157 Da
- GHK first reported
- Pickart and Thaler, Nature New Biology 1973;243(124):85–87
- GHK-Cu complex
- CAS 89030-95-5; also called prezatide copper and copper tripeptide-1
- Human trial data
- GHK-Cu: one 1994 randomised, vehicle-controlled trial. AHK-Cu: none located
- Head-to-head studies
- None located
Where the evidence stands
- Structure and copper binding
- Cell and ex-vivo work
- Animal work (GHK-Cu only)
- One human trial (GHK-Cu only)
The two compounds are at different stages of evidence entirely. AHK-Cu reaches the second rung; GHK-Cu reaches the fourth, once, in a formulated product.
One methyl group apart
GHK is the tripeptide glycyl-L-histidyl-L-lysine, formula C14H24N6O4, with a monoisotopic mass of 340.1859 and an average mass of 340.384. AHK is alanyl-L-histidyl-L-lysine, C15H26N6O4, monoisotopic 354.20155 and average 354.411. Both share the same His-Lys C-terminal pair; the only difference is at residue one, where glycine’s side chain is a hydrogen and alanine’s is a methyl group.
That single substitution adds one carbon and two hydrogens, which is 14.0157 Da monoisotopic — a figure we computed from the two curated masses and then reproduced from atomic masses. It is a small difference in absolute terms and an enormous one analytically, because 14 Da is far outside the error of any routine mass measurement.
A practical note on what you are actually buying: both are normally supplied as salts of the free peptide rather than as the copper complex. Sigma-Aldrich lists GHK as the acetate salt, CAS 72957-37-0, with a molecular weight of 400.43 and a stated peptide content of around 70 per cent alongside a purity of at least 97 per cent by thin-layer chromatography. Those are two different numbers measuring two different things, and the distinction matters when you read a certificate. Our guide to peptide notation and salt forms works through why a labelled mass is not peptide mass.
What the copper chemistry actually shows
Both tripeptides bind copper(II), and the His imidazole plus the peptide backbone nitrogens are the obvious candidates for coordination. What is often written next — a single clean 1:1 complex with a defined square-planar geometry — is more than the primary literature supports.
The most thorough study we could read is a 2001 paper in Biochimica et Biophysica Acta by Conato and colleagues, which examined copper complexes of GHK and two synthetic analogues using potentiometry, solution calorimetry, UV-visible spectroscopy, circular dichroism and EPR. Its abstract states that “all the ligands formed complexes having different stoichiometries and stabilities”, and reports evidence for binuclear species. It also found that the lysine side-chain amino group participates in complexation only at alkaline pH; at physiological pH it is protonated and does not.
The same work produced a structure-activity result worth knowing, because it cuts against the intuition that the histidine is doing all the work: the copper complex formed via the glycine residue appeared necessary for activity, the histidine residue showed no specific role, and the free lysine side chain appeared essential. Two analogues in which histidine was replaced matched or exceeded GHK’s in-vitro activity.
Reviews generally say only that GHK “has a high affinity for the copper 2+ ion”. We are deliberately not quoting a numerical stability constant here: the figure that circulates is attributed to a 2018 review whose full text, on our reading, does not contain it.
GHK-Cu: what is published, and in what model
GHK was first reported by Pickart and Thaler in Nature New Biology in 1973, volume 243, pages 85 to 87, in a paper about a tripeptide in human serum that prolonged the survival of normal liver cells. Later reviews by Pickart describe it as having been isolated from the albumin fraction of human plasma; the 1973 paper’s own title says serum. We flag that because the two words are used interchangeably in secondary accounts and they are not interchangeable.
The bulk of the GHK-Cu literature sits in cells and animals. A 2018 review in International Journal of Molecular Sciences catalogues the model systems, and reading it carefully is instructive about how much of the evidence is human: adult dermal fibroblasts in culture showing raised elastin and collagen; skin fibroblasts; lung fibroblasts from patients with COPD; several immortalised cell lines; transcriptional profiles from a gene-expression database; mice with LPS-induced lung injury; rabbit and rat wound models; and cortisone-inhibited healing in mice, rats and pigs. The human studies in that review are cosmetic-formulation studies of finished creams, with company-affiliated authors.
Two internal errors in that same review are worth recording, because they bear on how much weight it can carry: it reports a downregulation of “minus 475 per cent”, which is not a possible value for a decrease, and the reference it cites for 1983 sarcoma work is actually a paper about a glycylglycylhistidine complex, not GHK-Cu. For anything load-bearing, go to primary sources rather than that review.
There is, however, one genuine human randomised trial. Mulder and colleagues published a multicentre, randomised, evaluator-blinded, vehicle-controlled study in Wound Repair and Regeneration in 1994, in patients with diabetic neuropathic ulcers, all of whom received standardised wound care including sharp debridement. Median area closure was 98.5 per cent with the GHK-Cu preparation against 60.8 per cent with vehicle, with fewer infections; larger ulcers responded less well. Two caveats belong with that result: it tested a finished, formulated pharmaceutical wound gel, which is a different article from a research-grade vial of peptide, and it is a single trial from over three decades ago.
The antioxidant-gene claim, examined
If you have read about copper peptides anywhere, you have probably met the claim that GHK-Cu activates Nrf2, the transcription factor that governs a large antioxidant gene programme. We went looking for the functional study behind it and could not find one. Here is what the trail actually consists of.
What the source says. The claim traces to a 2015 review in Cosmetics by Pickart, Vasquez-Soltero and Margolina. In that paper the gene NFE2L2, which encodes Nrf2, appears exactly once — in a table, not in the body text — annotated “Nuclear respiratory factor 2 helps activate antioxidant responsive element-regulated genes”. That expansion is wrong: NFE2L2 is nuclear factor erythroid 2-related factor 2, a different protein from nuclear respiratory factor 2. There is no body-text discussion and no functional experiment. The gene-expression data are the authors’ own re-analysis of Connectivity Map profiles retrieved in March 2013, and the paper states that two of the three profiles came from the PC3 cell line and the third from MCF7 — both cancer cell lines, neither a fibroblast. All three authors list a single affiliation, the research and development department of a copper-peptide company, and the paper declares no conflict of interest.
A 2018 review by the same group does not mention Nrf2 or NFE2L2 at all in the text we were able to read. So the position is this: there is no published functional evidence that GHK or GHK-Cu activates Nrf2. The claim rests on one mislabelled row in a table, in a review, resting on a re-analysis of public cancer-cell-line data. If you want to understand what an Nrf2 claim would actually have to demonstrate, our article on Nrf2 and oxidative stress sets out the pathway and the standard of evidence; and how to read a peptide study covers the general move of treating a transcriptional signature as a mechanism.
AHK-Cu: the whole published record
This section is short because the literature is. A search of Europe PMC across titles, abstracts and full text for “AHK-Cu” returns five records for the entire database. Of those, one is a primary research article.
That article is Pyo and colleagues, 2007, in Archives of Pharmacal Research. It tested AHK-Cu only; GHK-Cu was not tested, and appears in the paper only as a citation in the reference list. The models were ex-vivo human hair-follicle organ culture and cultured human dermal papilla cells. There was no animal model. The reported findings were stimulation of follicle elongation ex vivo and of dermal papilla cell proliferation in vitro, with a raised Bcl-2 to Bax ratio and reduced cleaved caspase-3 and PARP. The reduction in apoptotic dermal papilla cells is reported in the paper’s own words as a decrease that “was not statistically significant”.
The remaining four records are a 2026 review, a case series of a multi-ingredient formulation, another review, and a paper on trace metals in cryogels. None is comparative. The 2026 review grades AHK-Cu’s evidence as experimental, ex vivo, and says its “specific signaling mechanism is less well characterized than GHK-Cu”, citing only the Pyo paper. It tabulates GHK-Cu and AHK-Cu in separate rows with separate citations; it does not compare them.
So: no animal data, no human data, one primary study, one endpoint family. That is the honest shape of it, and it is a long way from the way AHK-Cu is often presented as an established alternative to GHK-Cu.
Telling them apart on a certificate
A 14 Da gap is comfortable for any mass spectrometer, so an intact-mass measurement separates GHK from AHK without difficulty. There is a subtler trap, though, and it is worth stating because it limits what an intact mass proves.
| Question | Which measurement answers it | What it cannot tell you |
|---|---|---|
| Is this GHK or AHK? | Intact mass: about 340.2 against about 354.2 monoisotopic | Nothing — the 14 Da gap settles this |
| Is the sequence correct? | Tandem mass spectrometry, or sequencing | Intact mass alone cannot. Lys-His-Gly has the identical formula and mass to Gly-His-Lys |
| How much of the vial is peptide? | Net peptide content, separate from purity | A purity percentage. Sigma’s GHK acetate lists around 70 per cent peptide content alongside at least 97 per cent purity |
| Was the copper complex characterised, or the free peptide? | Reading which species the certificate names | The product name. Both are commonly supplied as free-peptide salts |
The sequence-isomer point is the one most often missed. A curated database entry exists for Lys-His-Gly with formula C14H24N6O4 and a monoisotopic mass of 340.18590 — identical to GHK. So a mass measurement that lands on 340.19 is consistent with GHK but does not by itself establish that the residues are in the right order. Confirming sequence needs fragmentation. Retention time does not settle it either, since retention is method-dependent. Our guide to reading a mass spectrum covers what fragmentation data looks like, and the COA guide covers what else a useful report contains.
What’s established and what isn’t
Reasonably well established
- GHK is Gly-His-Lys, C14H24N6O4; AHK is Ala-His-Lys, C15H26N6O4. They differ by one methyl group, 14.0157 Da.
- GHK was first reported by Pickart and Thaler in Nature New Biology in 1973.
- Both tripeptides bind copper(II), forming complexes of more than one stoichiometry, with binuclear species reported.
- GHK-Cu raised elastin and collagen markers in cultured human dermal fibroblasts and accelerated healing in several animal wound models.
- One randomised, vehicle-controlled human trial of a formulated GHK-Cu wound gel reported greater median ulcer area closure than vehicle.
- AHK-Cu stimulated hair-follicle elongation ex vivo and dermal papilla cell proliferation in vitro in a single 2007 study.
Open questions
- Whether either compound does anything comparable when applied as a research-grade peptide rather than in a finished formulation.
- Whether AHK-Cu has any effect in a whole animal or a person. No such data was located.
- How the two compare. No head-to-head study exists, so any ordering of them is inference.
- Whether GHK-Cu influences antioxidant gene expression at all. The Nrf2 claim has no functional study behind it.
- What the copper complex’s geometry and stoichiometry are under physiological conditions, given that multiple species form.
- Whether the 1994 ulcer result would replicate, more than thirty years on and with modern wound care as the comparator.
Sourcing copper tripeptides in Canada
Copper peptides raise one documentation question that ordinary peptides do not: which chemical species the certificate actually characterised.
- Check whether the report describes the free peptide, a salt, or the copper complex. These have different masses, and the product name rarely says which was measured.
- Look for peptide content as well as purity. They are different numbers. A high purity figure alongside a much lower peptide content is normal for an acetate salt, not a red flag — but you need both to know what you have.
- Treat an intact mass as identity, not sequence. Sequence isomers share a mass; fragmentation is what confirms the order.
- Match the batch number on the certificate to the one on your vial. Our GHK-Cu research guide covers the compound’s literature in more depth.
Research peptides with published test reports
Both tripeptides are in the catalogue as separate products, along with two blends that contain GHK-Cu. Janoshik test reports are listed by batch on our Lab Testing page.
Looking for copper peptides for skin rather than for the lab? Our GHK-Cu skincare is a separate line of cosmetics for external use, and the guide to copper peptides for skin explains how it fits into a routine. Never apply a research reagent to your skin.
GHK-CuThe tripeptide with the larger published literatureView product
AHK-CuThe alanine analogue, studied ex vivo in one 2007 paperView product
GHK-Cu + KPV BlendCo-formulated with the tripeptide KPVView product
GLOW BlendGHK-Cu with BPC-157 and TB-500View product
Research use only. Pure Peptides Canada products are laboratory reagents for in-vitro research, not for human or veterinary use. This article explains published research for education; it is not medical, dietary or dosing guidance.
Frequently asked questions
What is the difference between GHK-Cu and AHK-Cu?
Chemically, one methyl group. GHK is glycyl-L-histidyl-L-lysine and AHK is alanyl-L-histidyl-L-lysine, so they share the same histidine and lysine and differ only at the first residue. Alanine carries a methyl group where glycine carries a hydrogen, making AHK heavier by 14.0157 daltons monoisotopic. In published evidence the gap is much wider: GHK-Cu has cell, animal and one human randomised trial behind it, while for AHK-Cu we located a single primary study in ex-vivo and cultured cells.
Is there a study comparing GHK-Cu and AHK-Cu directly?
We could find no published head-to-head comparison of the two compounds. The one primary AHK-Cu paper we located tested AHK-Cu only, with GHK-Cu appearing just as a citation in its reference list. A 2026 review tabulates the two in separate rows with separate citations rather than comparing them, and describes AHK-Cu’s signalling mechanism as less well characterised. Any claim that one outperforms the other is therefore inference rather than evidence.
Does GHK-Cu activate Nrf2?
There is no published functional study showing that it does. The claim traces to a 2015 review in Cosmetics in which the gene NFE2L2, which encodes Nrf2, appears once in a table and nowhere in the body text, annotated with the wrong protein name. The underlying gene-expression data are the authors’ own re-analysis of public Connectivity Map profiles from the PC3 and MCF7 cancer cell lines, not their own experiments, and all three authors were affiliated with a copper-peptide company. A later review by the same group does not mention Nrf2 at all.
Has GHK-Cu been tested in people?
Yes, once, in a trial we were able to verify. Mulder and colleagues reported a multicentre, randomised, evaluator-blinded, vehicle-controlled study in patients with diabetic neuropathic ulcers in Wound Repair and Regeneration in 1994, with all patients receiving standardised wound care. Median area closure was 98.5 per cent with the GHK-Cu preparation against 60.8 per cent with vehicle. Two things qualify it: the trial tested a finished formulated wound gel rather than a research-grade peptide, and it is a single study from 1994.
Can a mass spectrometry result confirm I have GHK?
It can confirm the molecular formula but not the sequence. A curated database entry exists for Lys-His-Gly with exactly the same formula and the same monoisotopic mass of 340.18590 as Gly-His-Lys, so a mass landing on that value is consistent with GHK without establishing that the residues are in the right order. Confirming sequence requires fragmentation, meaning tandem mass spectrometry, or a sequencing method. Retention time does not settle it either, because retention depends on the method used.
Why does a GHK certificate show a purity figure and a lower peptide content?
Because they measure different things, and both are normal. Purity is the share of detected material that is the target compound. Peptide content is the share of the vial’s mass that is peptide rather than counter-ions and water, since these compounds are usually supplied as salts. Sigma-Aldrich’s GHK acetate salt, for instance, lists a purity of at least 97 per cent by thin-layer chromatography alongside a peptide content of around 70 per cent. Seeing both is more informative than seeing either alone.
Is GHK-Cu a single well-defined copper complex?
Not according to the physical chemistry. A 2001 study using potentiometry, calorimetry, UV-visible spectroscopy, circular dichroism and EPR reported that the ligands formed complexes of different stoichiometries and stabilities, with evidence for binuclear species, and found that the lysine side-chain amino group only participates in binding at alkaline pH rather than at physiological pH. Statements that assign a single geometry and a single 1 to 1 ratio go beyond what that work supports.
Copper tripeptides, documented by batch
GHK-Cu, AHK-Cu and the blends that contain them, priced in Canadian dollars and shipped tracked from inside Canada.
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;243(124):85–87. Bibliographic record consulted; article text not read.
- Conato C, Gavioli R, Guerrini R, Kozlowski H, Mlynarz P, Pasti C, Pulidori F, Remelli M. Copper complexes of glycyl-histidyl-lysine and two of its synthetic analogues: chemical behaviour and biological activity. Biochim Biophys Acta Gen Subj. 2001;1526(2):199–210. Abstract consulted. DOI
- Mulder GD, Patt LM, Sanders L, Rosenstock J, Altman MI, Hanley ME, Duncan GW. Enhanced healing of ulcers in patients with diabetes by topical treatment with glycyl-L-histidyl-L-lysine copper. Wound Repair and Regeneration. 1994;2(4):259–269. Abstract consulted. DOI
- Pyo HK, Yoo HG, Won CH, Lee SH, Kang YJ, Eun HC, Cho KH, Kim KH. The effect of tripeptide-copper complex on human hair growth in vitro. Arch Pharm Res. 2007;30(7):834–839. Abstract consulted. DOI
- Pickart L, Vasquez-Soltero JM, Margolina A. GHK-Cu may Prevent Oxidative Stress in Skin by Regulating Copper and Modifying Expression of Numerous Antioxidant Genes. Cosmetics. 2015;2(3):236–247. DOI
- Pickart L, Margolina A. Regenerative and Protective Actions of the GHK-Cu Peptide in the Light of the New Gene Data. Int J Mol Sci. 2018;19(7):1987. DOI
- Pickart L, Margolina A. Skin Regenerative and Anti-Cancer Actions of Copper Peptides. Cosmetics. 2018;5(2):29. DOI
- Sigma-Aldrich. Product G1887, Gly-His-Lys acetate salt; CAS 72957-37-0; stated peptide content and purity. Product page consulted.
- Chemical Entities of Biological Interest (ChEBI). Entry CHEBI:158225, L-alanyl-L-histidyl-L-lysine; and entry CHEBI:159994, Lys-His-Gly. European Bioinformatics Institute.
For laboratory research use only. Not for human or veterinary use. This article summarizes published research for educational purposes and is not medical advice.
