| Huang 2026 Eur J Pharm Sci Chemical characterisation | ChemistryNo organism Ball-milled co-amorphous mixtures GHK without copper | The study found that GHK fully amorphised three model compounds within 15 minutes of milling, whereas single amino-acid co-formers mostly left partly crystalline mixtures. | GHK is used here as an excipient, not studied as an active substance. | Evidence grade D |
| Ye 2026 Curr Issues Mol Biol Collagen and extracellular matrix · Skin research | In vitroCell culture Dermal fibroblasts Multi-ingredient product | The study measured elastin expression and secretion by dermal fibroblasts exposed to copper tripeptide-1, alongside two other ingredients tested for elastase and scaffold-gene effects. | Cell culture; combination study. | Evidence grade D |
| Mazzola 2026 Res Sq Non-topical routes | Animalintraperitoneal and intranasal Aged C57BL/6J mice (20–21 months) GHK-Cu (copper complex) | This preprint measured spatial-navigation escape latency and hippocampal gene expression and reported different, partly opposite, transcriptional programmes after intraperitoneal versus intranasal dosing. | Preprint, not peer reviewed; mice; the two routes also differed in duration. | Evidence grade C |
| Ogórek 2026 J Chromatogr A Laboratory analytical methods · Chemical characterisation | ChemistryNo organism Oil-in-water emulsion and serum cosmetic matrices GHK-Cu (copper complex) | The study measured the stability of liposome-encapsulated GHK-Cu after incorporation into model emulsion and serum formulations. | Model formulations; abstract truncated in PubMed. | Evidence grade D |
| Dkhar 2025 J Phys Chem B Laboratory analytical methods | ChemistryNo organism Solution GHK-Cu (copper complex) | The study designed donor–acceptor fluorescent probes selective for Cu(II) over competing metal ions and applied them to detecting copper tripeptide. | Sensor chemistry; not a validated quality-control assay. | Evidence grade D |
| Patel 2025 Cureus Skin research | Humantopical Women with acne scars Multi-ingredient product · n = Not reported in the abstract | The study assessed visible scar change on the Manchester Scar Scale by a dermatologist with a multi-ingredient gel. | No control group; four actives in one gel, so no attribution to the copper peptide. | Evidence grade B |
| Patel 2024 Cureus Hair research · Skin research | Humantopical Adults with mild-to-moderate scalp flaking Multi-ingredient product · n = Not reported in the abstract | The study measured adherent scalp flaking, scalp hydration, hair density and hair thickness over 15 days of a two-product regimen. | No control group; 15 days; two products and several actives, so no attribution to the copper peptide. | Evidence grade B |
| Zajda 2024 Electrophoresis Laboratory analytical methods | ChemistryNo organism Liposome preparations GHK-Cu (copper complex) | The study used CE-ICP-MS/MS copper and phosphorus signals to confirm liposome formation and to measure the amount of GHK-Cu encapsulated. | Method demonstration in model liposomes. | Evidence grade D |
| Jiang 2023 J Cosmet Dermatol Collagen and extracellular matrix · Skin research | Ex vivoCell culture Human dermal fibroblasts; ex vivo skin Multi-ingredient product | The study measured collagen I, IV and VII expression across GHK-Cu and hyaluronic acid ratios and reported collagen IV increases of 25.4-fold in cells and 2.03-fold in ex vivo skin at a 1:9 ratio. | Combination with hyaluronic acid; mRNA in cells and staining in excised skin. | Evidence grade D |
| Sahu 2023 J Org Chem Laboratory analytical methods | ChemistryNo organism Methanol solution GHK-Cu (copper complex) | The study reported a phenothiazine fluorescent sensor selective for Cu(II) over other transition-metal salts and applied it to GHK-Cu sensing. | Sensor chemistry; not a validated quality-control assay. | Evidence grade D |
| Dymek 2023 Pharmaceutics Laboratory analytical methods · Chemical characterisation | ChemistryNo organism Hydrogenated-lecithin liposomes GHK-Cu (copper complex) | The study prepared anionic and cationic liposomes of about 100 nm and measured GHK-Cu encapsulation efficiencies of 31.7 ± 0.9% (cationic) and 20.0 ± 2.8% (anionic) for the selected formulations. | Formulation characterisation; enzyme-inhibition assays are cell-free. | Evidence grade D |
| Lee 2022 Pharmaceutics Skin research | Ex vivotopical Pig and mouse skin in Franz diffusion cells GHK-Cu (copper complex) | The study found that all tested laser modalities increased skin permeation of the peptides in vitro, with non-ablative lasers disrupting the stratum corneum ultrastructure. | Animal skin; delivery outcome only. | Evidence grade D |
| Bossak-Ahmad 2021 Inorg Chem Copper binding · Chemical characterisation | ChemistryNo organism Aqueous solution with human serum albumin GHK-Cu (copper complex) | The study identified two ternary Cu(GHK)–albumin complexes formed through albumin histidine imidazoles, with His3 as one site (conditional constant 2,900 M⁻¹ at pH 7.4). | The second site is assigned only as likely His128 or His510. | Evidence grade D |
| Ufnalska 2021 Inorg Chem Copper binding · Chemical characterisation | ChemistryNo organism Aqueous solution GHK-Cu (copper complex) | The study characterised a transient glutathione–Cu(II)–GHK intermediate in the reduction of Cu(II)–GHK by glutathione and measured how temperature, oxygen and ternary ligands changed the reduction rate. | Chemical reaction study; the biological role proposed by the authors is a hypothesis. | Evidence grade D |
| Hur 2020 J Pept Sci Skin research · Collagen and extracellular matrix | In vitroCell culture Cell cultures and skin delivery models Derivative or conjugate | The study compared GHK with a tetra-arginine conjugate and found faster cellular penetration and higher in vitro collagen biosynthesis with the conjugate. | Conjugate differs from GHK-Cu; the authors attribute part of the effect to the arginine tail itself. | Evidence grade D |
| Bossak-Ahmad 2020 Int J Mol Sci Copper binding · Chemical characterisation | ChemistryNo organism Aqueous solution GHK-Cu (copper complex) | The study found that cis-urocanic acid also coordinates Cu(II) and that GHK, Cu(II) and cis-urocanic acid form a ternary complex. | The physiological relevance is inferred from published tissue concentrations, not measured in tissue. | Evidence grade D |
| Kapoor 2020 Plast Reconstr Surg Glob Open Hair research · Safety and tolerability data · Non-topical routes | Animalintradermal Human keratinocyte and fibroblast assays; animal hair-growth model Multi-ingredient product | The study measured cytotoxicity of each ingredient in keratinocyte and fibroblast assays and hair growth after intradermal injection of the full formulation in animals. | Multi-ingredient; authors connected to the formulation; abstract truncated in PubMed. | Evidence grade C |
| Kapoor 2018 J Cosmet Laser Ther Hair research · Non-topical routes | Humanintradermal Adults with hair loss Multi-ingredient product · n = 1000 | The study assessed hair regrowth and adverse events after repeated intradermal scalp injections of a multi-ingredient formulation. | No control group; at least six actives, so no effect or safety finding can be attributed to copper tripeptide-1. | Evidence grade B |
| Beuning 2018 Inorg Chem Copper binding · Laboratory analytical methods | ChemistryNo organism Aqueous solution GHK-Cu (copper complex) | The study measured second-order rate constants for Cu(II) transfer from a tryptophan analogue complex to GHK of 1.6 × 10² M⁻¹ s⁻¹ and to DAHK of 5.0 × 10¹ M⁻¹ s⁻¹. | Model exchange reaction using a substituted peptide as the copper donor. | Evidence grade D |
| Tanaka 2018 J Clin Aesthet Dermatol Hair research · Non-topical routes | Humanintradermal Men treated in one clinic, 2011–2017 Multi-ingredient product · n = 18,918 treated | The series assessed pre- and post-treatment photographs of men given a combination regimen in which copper tripeptide was one of many ingredients of one component. | Uncontrolled; approved drugs in the same regimen; the copper peptide contribution cannot be separated. | Evidence grade B |
| Wang 2017 Wound Repair Regen Collagen and extracellular matrix · Skin research | Animaltopical HUVEC cultures; mouse scald model GHK-Cu (copper complex) | The study measured a 33.1% higher endothelial-cell proliferation rate with GHK-Cu liposomes and compared CD31 and Ki67 staining and healing time in mice treated with liposomal versus free GHK-Cu. | Mice; liposomal formulation; abstract truncated in PubMed. | Evidence grade C |
| Badenhorst 2016 Pharm Dev Technol Chemical characterisation · Laboratory analytical methods | ChemistryNo organism Aqueous buffers, octanol–PBS, stress conditions GHK-Cu (copper complex) | The study measured hydrolytic degradation under basic and oxidative stress (less under acid), stability in water and pH 4.5–7.4 buffers for at least two weeks at 60 °C, and three degradation products by HPLC-MS, one being histidine. | Preformulation data for one material source; no product or shelf-life study. | Evidence grade D |
| Byun 2016 J Cosmet Laser Ther Skin research · Collagen and extracellular matrix | Humantopical One adult, periocular skin Multi-ingredient product · n = 1 | The case report described photographs and biopsy staining (collagen, fibrillin-1, procollagen type 1) from treated and untreated areas in one person. | One person; five active ingredients plus a device; cannot attribute any finding to GHK-Cu. | Evidence grade B |
| Lee 2016 Ann Dermatol Hair research | Humantopical Men with pattern hair loss Derivative or conjugate · n = 45 | The study measured hair count, length and thickness at 1, 3 and 6 months; hair-count change differed from placebo in the lower-strength group, while length and thickness did not differ between groups. | Copper-free GHK complexed with 5-ALA, so it is not a GHK-Cu study; small groups; single centre. | Evidence grade B |
| Li 2016 Sci Rep Skin research · Safety and tolerability data | In vitroCell culture Human keratinocyte model GHK-Cu (copper complex) | The study compared irritation potential at the same concentrations and found GHK-Cu not cytotoxic and without significant change in the irritation markers measured, while the copper salts differed. | Keratinocyte culture model; not a human patch test; tested concentrations are those of the paper. | Evidence grade D |
| Li 2015 Pharm Res Skin research · Safety and tolerability data | Ex vivotopical Two in vitro skin models; cell and pig models for safety GHK-Cu (copper complex) | The study found that microneedle depth depended on application force and measured 134 ± 12 nmol of peptide and 705 ± 84 nmol of copper permeating through microneedle-treated skin in 9 hours. | Delivery study; does not measure any skin outcome in people. | Evidence grade D |
| Gruchlik 2014 Acta Pol Pharm Skin research | In vitroCell culture Normal human dermal fibroblasts GHK-Cu (copper complex) | The study measured IGF-2-dependent TGF-β1 secretion by dermal fibroblasts exposed to 1 nM GHK, GHK-Cu or copper chloride. | Abstract truncated in PubMed; single cell type. | Evidence grade D |
| Parker 2013 Otolaryngol Head Neck Surg Collagen and extracellular matrix · Skin research | Animaltopical Irradiated rat dorsal skin flaps GHK-Cu (copper complex) · n = 23 (13 test, 10 control) | The study measured ischaemic flap area, caveolin-1 and VEGF staining; mean ischaemic area was 5.0 cm² with GHK-Cu gel and 3.8 cm² with the control ointment. | Rats; the measured ischaemic area was larger in the GHK-Cu group. | Evidence grade C |
| Trapaidze 2012 J Biol Inorg Chem Copper binding · Chemical characterisation | ChemistryNo organism Aqueous buffer, pH 7.4 GHK-Cu (copper complex) | The study measured predominantly 1:1 binding and a conditional dissociation constant at pH 7.4 of 7.0 × 10⁻¹⁴ M for GHK (2.6 × 10⁻¹⁴ M for DAHK), with the enthalpic and entropic contributions. | Conditional constant: valid for the stated pH and with competitor and buffer contributions removed. | Evidence grade D |
| Choi 2012 J Pept Sci Skin research | In vitroCell culture Normal human keratinocytes; skin-equivalent models GHK without copper | The study measured keratinocyte proliferation and staining for integrins α6 and β1, p63 and PCNA in skin equivalents cultured with copper-free GHK. | Cultured cells and engineered tissue. | Evidence grade D |
| Gruchlik 2012 Acta Pol Pharm Skin research | In vitroCell culture Normal human dermal fibroblasts (NHDF) GHK-Cu (copper complex) | The study measured TNF-α-dependent IL-6 secretion and reported decreases with GHK, GGH, copper chloride and their copper complexes. | Single cell type; copper chloride alone also changed the readout. | Evidence grade D |
| Hostynek 2011 Inflamm Res Skin research · Laboratory analytical methods | Ex vivotopical Human skin layers in flow-through diffusion cells GHK-Cu (copper complex) | The study reported the same permeability coefficient (2.43 ± 0.51 × 10⁻⁴ cm/h) and 136.2 µg/cm² copper permeated, with 97 µg/cm² retained in dermatomed skin. | Near-duplicate of the 2010 report by the same group with a different retained-copper figure; measures copper, not intact peptide. | Evidence grade D |
| Hureau 2011 Chemistry Copper binding · Chemical characterisation | ChemistryNo organism Single crystals and aqueous solution GHK-Cu (copper complex) | The study reported a dimeric Cu(II)–GHK structure in the solid state and a monomer in solution with three nitrogen ligands (glycine amine, deprotonated amide and histidine imidazole) and a labile oxygen in the fourth equatorial position. | No openly licensed copy of the coordinates was found (Crystallography Open Database searched 2026-11-11), so this site does not render them. | Evidence grade D |
| Hostynek 2010 Inflamm Res Skin research · Laboratory analytical methods | Ex vivotopical Human skin layers in flow-through diffusion cells GHK-Cu (copper complex) | The study measured a permeability coefficient through dermatomed skin of 2.43 ± 0.51 × 10⁻⁴ cm/h, with 136.2 µg/cm² copper permeated over 48 h and 82 µg/cm² retained. | Measures copper, not intact peptide; infinite-dose conditions; excised skin. | Evidence grade D |
| Chirita 2009 Anal Chim Acta Laboratory analytical methods | ChemistryNo organism Cosmetic creams Derivative or conjugate | The study validated an LC-MS/MS method (quantification limits, linearity, accuracy, precision) for palmitoyl peptides in creams, using palmitoyl-GHK as the internal standard. | Pal-GHK is the internal standard, not the analyte. | Evidence grade D |
| Trookman 2009 J Clin Aesthet Dermatol Skin research | Humantopical Women 22–40 with mild-to-moderate lip dryness Multi-ingredient product · n = 32 | The study measured visual grading, corneometry, lip caliper dimensions and self-assessment over four weeks of a multi-ingredient lip product. | No control group; palmitoyl-GHK is one of many ingredients and not GHK-Cu, so no effect can be attributed to it. | Evidence grade B |
| Mazurowska 2008 J Cosmet Sci Skin research | Ex vivotopical Skin barrier models GHK-Cu (copper complex) | The study measured penetration of copper complexes of GHK and of glutathione through the stratum corneum in vitro. | Abstract truncated in PubMed; in vitro barrier model. | Evidence grade D |
| Beretta 2008 J Pharm Biomed Anal Chemical characterisation · Laboratory analytical methods | ChemistryNo organism Phosphate buffer, pH 7.4 GHK without copper | The study characterised the products of GHK reacting with acrolein by ESI-MS/MS and found sequential addition of up to three acrolein molecules, including at the lysine ε-amine. | Cell-free chemistry. | Evidence grade D |
| Huang 2007 Photomed Laser Surg Collagen and extracellular matrix | In vitroCell culture Human fibroblast line HS68 GHK-Cu (copper complex) | The study measured fibroblast viability, procollagen type I C-peptide and bFGF with LED light alone or combined with Cu-GHK. | Cell line; combined with a light treatment; abstract truncated in PubMed. | Evidence grade D |
| Beretta 2007 Chem Res Toxicol Chemical characterisation | ChemistryNo organism Phosphate buffer, pH 7.4 GHK without copper | The study measured HNE consumption in the presence of GHK, confirmed GHK–HNE adducts by mass spectrometry and NMR, and found GHK less potent than carnosine as an HNE quencher. | Cell-free chemistry at millimolar peptide concentration. | Evidence grade D |
| Mazurowska 2007 Talanta Laboratory analytical methods · Skin research · Copper binding | ChemistryNo organism Flynn diffusion cell with a liposome model membrane GHK-Cu (copper complex) | The study identified the copper complexes present at different pH by ESI-MS and measured permeability coefficients through a model stratum corneum membrane that increased with pH. | Artificial membrane, not skin. | Evidence grade D |
| Miller 2006 Arch Facial Plast Surg Skin research | Humantopical Adults after circumoral CO₂ laser resurfacing GHK-Cu (copper complex) · n = 13 completed | The trial found no significant difference in resolution of post-laser redness, wrinkles or overall skin quality on objective and blinded assessment; only patient-reported satisfaction differed (P = .04). | 13 completers; primary objective measures were null. | Evidence grade A |
| Cangul 2006 Vet Dermatol Collagen and extracellular matrix · Skin research | Animaltopical New Zealand rabbits, full-thickness dorsal wounds GHK-Cu (copper complex) · n = 18 | The study measured unhealed wound area and contraction on days 7, 14 and 21; the copper-complex group had smaller unhealed areas than the untreated group at each time point. | Rabbits; small groups. | Evidence grade C |
| Pollard 2005 Arch Facial Plast Surg Skin research | In vitroCell culture Primary human dermal fibroblasts, normal and previously irradiated, serum-free GHK-Cu (copper complex) | The study measured faster population-doubling times in normal and irradiated fibroblasts exposed to GHK-Cu than in untreated controls, and their bFGF, TGF-β1 and VEGF output. | Cultured cells from surgical specimens. | Evidence grade D |
| Canapp 2003 Vet Surg Collagen and extracellular matrix · Skin research | Animaltopical Rat full-thickness wounds in an ischaemic skin flap GHK-Cu (copper complex) · n = 24 | The study measured wound area daily for 13 days and TNF-α, MMP-2 and MMP-9 in biopsies; wound area decreased in the gel group but not the vehicle group compared with no treatment. | Rats; abstract truncated in PubMed. | Evidence grade C |
| McCormack 2001 Arch Facial Plast Surg Skin research | In vitroCell culture Primary human facial dermal fibroblasts (normal and keloid-derived), serum-free GHK-Cu (copper complex) | The study measured fibroblast viability and secretion of basic FGF and TGF-β1 after copper tripeptide or tretinoin exposure. | Primary cell lines from surgical samples; abstract truncated in PubMed. | Evidence grade D |
| Conato 2001 Biochim Biophys Acta Copper binding · Chemical characterisation | ChemistryNo organism Aqueous solution; human serum (stability) GHK-Cu (copper complex) | The study measured complex stoichiometries and stabilities, reported binuclear species, and concluded that the lysine side-chain amine joins the copper complex only at alkaline pH and stays protonated at physiological pH. | The serum-stability measurement covered the synthetic analogues for 3 hours. | Evidence grade D |
| Siméon 2000 Life Sci Collagen and extracellular matrix | In vitroCell culture Dermal fibroblast cultures GHK-Cu (copper complex) | The study measured higher MMP-2, TIMP-1 and TIMP-2 secretion with GHK-Cu; copper ions reproduced the MMP-2 effect and GHK alone did not. | Cultured cells; the copper-only result complicates attribution to the complex. | Evidence grade D |
| Siméon 2000 J Invest Dermatol Collagen and extracellular matrix | Animalwound chamber Rat wound-chamber model and rat dermal fibroblasts GHK-Cu (copper complex) | The study measured increased wound-tissue dry weight, protein, type I collagen and glycosaminoglycans with repeated GHK-Cu injections, with greater chondroitin and dermatan sulfate accumulation. | Rats; chamber delivery. | Evidence grade C |
| Siméon 1999 J Invest Dermatol Collagen and extracellular matrix | Animalwound chamber Rat wound-chamber model GHK-Cu (copper complex) | The study measured matrix metalloproteinase expression and activation in wound fluid; GHK-Cu did not alter interstitial collagenase activity and changed MMP-2 and MMP-9 profiles. | Rats; chamber delivery; abstract truncated in PubMed. | Evidence grade C |
| Endo 1997 J Chromatogr B Biomed Sci Appl Laboratory analytical methods · Non-topical routes | Chemistryintravenous Rat plasma GHK without copper | The method reached detection limits of 50 ng/mL (GHK) and 15 ng/mL (His-Lys) in rat plasma; in the applied rat study, intravenously given GHK was rapidly degraded to His-Lys, which was rapidly eliminated. | Rats only; copper-free peptide; the abstract gives no half-life values. | Evidence grade D |
| Pesáková 1995 Biomaterials Collagen and extracellular matrix | In vitroCell culture Chick embryo chondrocytes on three supports GHK-Cu (copper complex) | The study measured chondrocyte proliferation and synthesis of collagen types I, II and III with the copper-tripeptide supplement on plastic and collagen supports. | Avian cells; biomaterials context; abstract truncated in PubMed. | Evidence grade D |
| Godet 1995 Cell Mol Biol (Noisy-le-grand) Collagen and extracellular matrix | In vitroCell culture Rat calvaria cells, human trabecular osteoblasts, human marrow stromal cells GHK-Cu (copper complex) | The study found that GHK-Cu and GHK coatings (10⁻¹⁰–10⁻⁸ M) did not change cell spreading but increased the attachment of rat and human osteoblastic cells. | Cultured cells on coated surfaces. | Evidence grade D |
| Buffoni 1995 Arch Int Pharmacodyn Ther Collagen and extracellular matrix · Skin research | Animaltopical Guinea-pig dorsal skin wounds; cultured fibroblasts GHK-Cu (copper complex) | The study measured hydroxyproline, protein, DNA and amine-oxidase activity and observed slower skin reorganisation and delayed fibroblast activation with the copper-peptide complexes. | Guinea pigs; findings run opposite to several other animal reports. | Evidence grade C |
| Mulder 1994 Wound Repair Regen Skin research · Collagen and extracellular matrix | Humantopical Adults with neuropathic plantar ulcers GHK-Cu (copper complex) · n = Not reported in the abstract | The trial reported median plantar-ulcer area closure of 98.5% with the gel vs 60.8% with vehicle (p < 0.05), a larger difference in ulcers over 100 mm², and fewer ulcer infections (7% vs 34%). | Sample size not given in the abstract; one 1994 topical gel; the authors note the effect depended on starting immediately after debridement. No independent replication is indexed. | Evidence grade A |
| Maquart 1993 J Clin Invest Collagen and extracellular matrix | Animalwound chamber Rat wound-chamber model (mesh chamber implanted under the skin) GHK-Cu (copper complex) | The study measured concentration-dependent increases in dry weight and connective-tissue components (collagen, DNA, glycosaminoglycans) in GHK-Cu-injected wound chambers compared with saline. | Rats; material delivered directly into an implanted chamber, which is not a route of administration to a person. | Evidence grade C |
| Bishop 1992 J Vasc Surg Skin research · Collagen and extracellular matrix | Humantopical Adults with venous leg ulcers GHK-Cu (copper complex) · n = 86 evaluable | The trial measured ulcer size: silver sulfadiazine reduced it more than the copper tripeptide cream or placebo, and there was no difference between the copper tripeptide cream and placebo. | Single trial of one 1992 topical formulation; the comparison with placebo was null. | Evidence grade A |
| Wegrowski 1992 Life Sci Collagen and extracellular matrix | In vitroCell culture Normal human fibroblast cultures GHK-Cu (copper complex) | The study measured a biphasic increase in glycosaminoglycan synthesis, maximal at 10⁻⁹–10⁻⁸ M and returning to control at higher concentrations, mainly dermatan sulfate and heparan sulfate. | Cultured cells. | Evidence grade D |
| Maquart 1988 FEBS Lett Collagen and extracellular matrix | In vitroCell culture Fibroblast cultures GHK-Cu (copper complex) | The study measured collagen synthesis in fibroblast cultures that rose from 10⁻¹²–10⁻¹¹ M GHK-Cu and peaked at 10⁻⁹ M, independent of cell number. | Cultured cells; the wound-site liberation hypothesis is the authors’ suggestion. | Evidence grade D |
| Laussac 1983 Biochem J Copper binding · Chemical characterisation | ChemistryNo organism Aqueous solution GHK-Cu (copper complex) | The EPR spectra between pH 6.0 and 9.6 showed seven-line nitrogen superhyperfine splitting, read by the authors as three nitrogen atoms coordinated to Cu(II); the study cautioned that NMR line broadening mainly reflected minor species. | Spectroscopic inference; no crystal structure in this paper. | Evidence grade D |
| Freedman 1982 Biochemistry Copper binding · Chemical characterisation | ChemistryNo organism Aqueous solution GHK-Cu (copper complex) | The study found a mononuclear 1:1 complex at neutral pH with Cu(II) equatorially bound by two or three nitrogen atoms, one of them in the histidine imidazole ring, and transitions with apparent pK values of 3.6, 9.2 and 11.4. | Solution structure inferred from spectroscopy; differs from the oxygen-bridged solid-state structure. | Evidence grade D |
| Lau 1981 Biochem J Copper binding · Chemical characterisation | ChemistryNo organism Aqueous solution, 25 °C, 0.15 M NaCl GHK-Cu (copper complex) | The study measured multiple Cu(II)–GHK species across pH 3.5–10.6, derived their stability constants, and found by equilibrium dialysis that GHK competed with albumin for Cu(II) at pH 7.5. | Solution equilibria at fixed temperature and ionic strength; species assignments are proposed from the data. | Evidence grade D |
| Pickart 1980 J Cell Physiol Copper binding | In vitroCell culture Human plasma fractions; rat hepatoma cell line (HTC4) GHK-Cu (copper complex) | The study reported that GHK in plasma was associated with copper and iron, and that at physiological pH in vitro it associated with several transition-metal ions but not with calcium, potassium or sodium. | 1980 methods; the cell-growth findings are in a single transformed cell line. | Evidence grade D |
| Rabenstein 1977 Biochemistry Chemical characterisation | ChemistryNo organism Aqueous solution, proton NMR GHK without copper | The study measured the acid dissociation constants of the glycyl amine, histidyl imidazole and lysyl amine groups; the lysyl amine titrated over a much higher pH range than the other two groups. | Copper-free peptide; solution chemistry only. | Evidence grade D |
| Schlesinger 1977 Experientia Chemical characterisation | ChemistryNo organism Human serum fraction GHK without copper | This 1977 report identified the growth-modulating tripeptide isolated from human serum as glycyl-histidyl-lysine. | No abstract is indexed; the identification is reported from the title and later citing work. | Evidence grade D |