# GHK-Cu: The Copper-Tripeptide Literature, Pressed Plate by Plate > GHK-Cu is the glycyl-L-histidyl-L-lysine copper(II) complex, an endogenous plasma tripeptide that stimulates collagen synthesis, follicle repair, and modulates about a third of human genes in study models. A cited literature herbarium. Each study is pressed and pinned here as its own specimen plate — the dose, the species, the route, and the honest gap beside it. Every quantitative claim is cited to its paper. ## What the GHK-Cu record holds GHK-Cu is the glycyl-L-histidyl-L-lysine copper(II) complex — a copper-binding tripeptide present endogenously in human plasma, saliva, and urine. It was first isolated by Loren Pickart in 1973 as a plasma factor that caused aged human liver tissue to synthesize proteins like younger tissue [6]. The molecule carries a single Cu(II) ion in a 1:1 chelate (molecular weight 402.92 Da), and the same Gly-His-Lys sequence appears inside the alpha-2(I) chain of type I collagen and in SPARC/osteonectin — a motif clipped from living tissue and, here, mounted plate by plate. The research record is wide and unusually quantitative for a peptide. In human fibroblast cultures, GHK-Cu stimulated collagen synthesis beginning between 10^-12 and 10^-11 M and peaking near 10^-9 M, with no change in cell number — a specific metabolic effect rather than a growth response [1]. Gene-expression analyses report that GHK modulates roughly 31.2% of human genes at a 50%-or-greater change threshold, upregulating wound-repair, DNA-repair, and antioxidant programs [2]. Plasma GHK itself declines with age, from about 200 ng/mL at age 20 to about 80 ng/mL by age 60 [3]. The most-cited clinical signals are dermatologic: topical GHK-Cu raised procollagen in 70% of treated subjects versus 40% for retinoic acid in reviewed trials [9], and a 6-month hair-count RCT of a GHK-containing complex beat placebo significantly [4]. This site reads that literature as a naturalist reads a folio: one specimen at a time, labelled by what it can bear. The flagship lenses are skin and the dermal matrix, the hair follicle, and — as the most recently pressed specimens — the 2023-2024 neuroprotection work, where free GHK prevented copper-induced CNS cell death in vitro [10] and intranasal GHK improved memory in aged and Alzheimer-model mice [8]. Browse the [copper peptide skin research](/skin-research), the [copper peptide hair growth research](/hair-growth), and the [GHK-Cu neuroprotection research](/research), or start with the [frequently asked questions about GHK-Cu](/faq). Where the evidence stops — and for systemic human use it stops early — the margin says so. ## What Is a Copper Peptide? A copper peptide is a short amino-acid chain that binds a copper(II) ion and carries it as a stable, reactivity-modified complex. The copper peptide class is defined by this chelation: the peptide scaffold holds the metal through multiple coordination sites, which raises its stability constant and changes how the copper behaves in tissue. In GHK-Cu, the Cu(II) ion is held through the histidine imidazole nitrogen, the glycine alpha-amino nitrogen, and a deprotonated amide nitrogen, leaving the lysine side chain free. GHK-Cu is the most-studied member of the class — its copper stability constant is very high (log K approximately 16.4), far above that of the free peptide, which limits release of pro-oxidant free copper [7]. That stability is what separates a copper peptide from loose copper salts. A free copper ion is a reactive pro-oxidant; bound inside the GHK scaffold, the same metal is delivered as a controlled, biologically legible signal. The blue-violet color of a reconstituted GHK-Cu solution is the expected Cu(II) absorption and the visible sign of an intact complex [7]. The distinction between the metal-bound and metal-free forms matters throughout this literature. GHK is the free tripeptide (MW 340.38); GHK-Cu is its copper chelate (MW 402.92). Copper coordination is required for most documented matrix-remodeling activities — the free peptide does not reproduce MMP-2 stimulation in fibroblast cultures [1]. When this site says "copper peptide," it means the chelated complex unless a study explicitly used free GHK, which several neuroprotection papers did. Reading the [GHK vs GHK-Cu](/research) distinction carefully is the single most useful habit for interpreting any claim in this folio. ## GHK Copper Peptide: The Copper-Binding Tripeptide Studied for Tissue Repair The GHK copper peptide acts as both a copper chaperone and a pleiotropic signaling molecule. At picomolar-to-nanomolar concentrations it directly stimulates dermal fibroblast synthesis of collagen, elastin, glycosaminoglycans, and the proteoglycan decorin, while rebalancing matrix metalloproteinases against their TIMP inhibitors [3]. The copper ion enables lysyl-oxidase-mediated collagen and elastin cross-linking and a superoxide-dismutase-like antioxidant activity. The effect is regulatory, not structural: the peptide does not become part of the new collagen — it instructs the cell to make more. In tissue-remodeling reviews, GHK-Cu increases protein synthesis of collagen, elastin, VEGF, FGF-2, NGF, neurotrophins 3 and 4, and erythropoietin, while suppressing free radicals, thromboxane, TGF-beta-1, TNF-alpha, and protein glycation, and chemoattracting macrophages, mast cells, and capillary cells to a wound [6]. This is the angiogenic-plus-antioxidant-plus-matrix-regulatory profile that recurs across the skin, hair, and wound literature — the same molecule doing the same kinds of things in dermis, follicle, and granulation tissue. The recurrence is itself a finding: across five decades and many models, the copper peptide keeps producing a controlled-repair signature rather than a single narrow effect. The [doses studied in the GHK-Cu literature](/dosage) span picomolar cell-culture concentrations to topical formulations of roughly 0.05% to 2%, and the [GHK-Cu side effects and safety](/dosage) record is dominated by topical cosmetic use rather than systemic dosing. That asymmetry — deep topical and dermatologic evidence, thin systemic human data — is the honest shape of the record, and it frames every page here. --- A dried herbarium of the GHK-Cu copper-tripeptide literature, pressed plate by plate and traced to its paper — the place where the materia is catalogued and studied, never a clinic, a counter, or anything dispensed.