GHK-CU 100 mg

Compound profile

GHK-Cu: compound profile, literature landscape and handling notes

Where GHK-Cu came from

The tripeptide entered the literature in the 1970s as an activity rather than as a molecule. Work on human plasma fractions reported that something in plasma modulated the behavior of hepatic tissue in culture, and that the effect differed between fractions from younger and older donors. Purification of that activity converged on a very small peptide, and the sequence turned out to be glycyl-L-histidyl-L-lysine. At that stage it was described as a growth-modulating factor, and the copper had nothing to do with the story.

The copper-binding property was recognized afterward, and it reframed the compound completely. The tripeptide has a donor-atom arrangement that binds copper(II) with high affinity under physiological conditions, and once that was appreciated it became clear that most of the reported activity tracked the complex rather than the free ligand. Preparations that had been characterized as GHK were, in plasma or in serum-containing medium, almost certainly GHK-Cu. Modern work generally specifies the complex, and the naming convention GHK-Cu exists precisely to force that distinction.

Two further points about provenance matter for how the record should be read. The first is that GHK is a real human sequence rather than a synthetic construct. It appears within the collagen alpha-2(I) chain and is described in the literature as being liberated by proteolysis during tissue remodeling, which gives it a plausible endogenous source and makes it one of the very few compounds in this catalog with a non-hypothetical physiological counterpart.

The second is that a large share of the GHK corpus, including several of the most-cited review articles, traces back to a small number of investigators with continuous involvement in the field since the original isolation. This is not an accusation; it is a structural feature of the literature that affects how much independent confirmation any given claim actually has. The frequently repeated statement that plasma GHK abundance declines substantially with age is the clearest example. It is asserted far more often than it is measured, the underlying measurements are few and old, and the figure gets passed from review to review without anyone returning to a primary determination.

Reading the structure of GHK-Cu

Three residues, in the order glycine, histidine, lysine, with a free N-terminal amine and a free C-terminal carboxylate. The sequence, formula and mass for this listing appear in the specification table further down this page. What that table cannot convey, and what actually defines the compound, is the coordination chemistry.

Copper(II) in GHK-Cu is held by nitrogen donors contributed by the first two residues. The alpha-amino nitrogen of the glycine, the deprotonated amide nitrogen of the peptide bond between glycine and histidine, and an imidazole nitrogen of the histidine side chain form the primary coordination sphere. The fourth equatorial position is occupied by an exchangeable ligand, which in practice means water, a buffer component, or a donor atom from another molecule in solution. This gives an approximately square-planar arrangement, the geometry expected for a d9 copper(II) center subject to Jahn-Teller distortion, with weak axial interactions completing the picture.

The deprotonated amide nitrogen is the feature to hold on to, because it is what makes the complex pH-dependent in a way that a plain peptide never is. Amide nitrogens are not acidic in isolation; they only deprotonate because the metal center stabilizes the resulting anion. Take the pH down and that stabilization is lost, the amide reprotonates, and the complex comes apart. This is why the speciation of GHK-Cu is a function of pH rather than a fixed property of the powder.

The lysine side chain sits outside the coordination sphere entirely. It is not a donor, but it is not inert either. Its protonated epsilon-amino group carries positive charge that affects solubility, chromatographic retention and interaction with polyanionic matrix components, and in a physiological setting the lysine face is implicated in ternary complex formation with serum albumin, which has its own high-affinity N-terminal copper site. The relevant species in serum-containing medium is therefore frequently not the isolated binary complex.

One consequence of all this deserves emphasis because it has no analog anywhere else in the catalog: the ratio of peptide to copper is a genuine specification parameter. A plain peptide has a sequence and a purity. A metal complex has a sequence, a purity, and a stoichiometry, and material sold at a nominal one-to-one ratio can in practice carry excess free ligand or, worse, excess uncomplexed copper.

The target and the pathway in more detail

There is no GHK-Cu receptor. Searching for one is the single most common conceptual error made about this compound, and the published mechanistic work does not support the framing. What the literature actually describes is better summarized as copper-dependent enzyme cofactor logistics: the complex participates in the movement of copper between ligands of differing affinity, and the downstream observations follow from where the copper ends up.

Copper in biological systems is never free. It is handed between proteins in a thermodynamic hierarchy, and the relevant partners named in the GHK literature include serum albumin, which has a dedicated high-affinity N-terminal site, ceruloplasmin as the dominant circulating copper protein, metallothioneins as high-capacity intracellular sinks, and cuproenzymes that require the metal to function. The stability of GHK-Cu sits in an intermediate window, high enough to hold copper against casual competition and low enough that transfer to stronger acceptors remains accessible. That intermediate position is exactly what makes a shuttle role plausible and also exactly what makes the compound behave differently in defined medium, in serum-containing medium and in a tissue matrix. Direction of transfer is a property of the system, not of the vial.

Two cuproenzymes recur throughout the work. Lysyl oxidase, which requires copper and initiates the covalent cross-linking of collagen and elastin, connects copper availability directly to extracellular-matrix maturation. Copper-zinc superoxide dismutase connects it to antioxidant capacity. Neither of these is activated by GHK-Cu in a receptor sense; the proposed relationship is cofactor supply.

Beyond the enzymes, the reported effects concentrate on extracellular-matrix gene expression. Published work describes changes in collagen transcripts, in glycosaminoglycan and proteoglycan synthesis, and in the balance between matrix metalloproteinases and their tissue inhibitors, the TIMPs. That balance is the more interesting readout of the two, because a compound that raised both synthesis and degradation would look very different in a remodeling assay from one that shifted the ratio.

Finally there is a substantial body of cell-culture observation on fibroblast behavior, including proliferation, migration and matrix deposition, with a smaller keratinocyte literature alongside it. These are the assays where an effect is most reproducibly reported and also where copper artifacts are hardest to exclude.

What the published literature on GHK-Cu actually measures

The GHK-Cu literature is large, old and unusually heterogeneous in quality, and sorting it by type before citing anything from it saves a great deal of trouble.

The first and most defensible body of work is dermatological and wound-model research in animals. These studies typically apply the complex in a controlled injury model and score closure, tensile properties of the repaired tissue, histology and matrix composition. The models are standard, the endpoints are measurable, and the reported direction of effect is reasonably consistent across groups. This is the part of the record that most resembles conventional preclinical pharmacology, and it is the part worth citing when the question is whether the compound does anything at all in a living tissue.

The second body is cell culture: fibroblasts, keratinocytes and to a lesser extent endothelial and neural cell models, with proliferation, migration, matrix protein output and enzyme activity as readouts. Concentrations used span a wide range, and the useful studies are the ones that include a copper-salt control arm and a free-peptide arm rather than only vehicle. Many do not.

The third body is gene-expression profiling. There is a well-known set of analyses reporting broad transcriptional shifts in fibroblasts exposed to the complex, sometimes framed through comparison against reference expression databases. These are hypothesis-generating datasets. They report that transcript abundance changed, which is not the same claim as that a function changed, and the gap between those two statements is where most over-reading of this compound happens.

The fourth body is cosmetic science, and it is the largest by sheer count. It ranges from careful formulation and stability work, which is genuinely useful because it addresses how the complex survives in a real matrix, to small, uncontrolled, unblinded, industry-funded panel studies of multi-ingredient preparations in which the complex is one component among many. A study of a finished formulation cannot attribute an effect to any single ingredient in it, and a great deal of secondary writing about GHK-Cu does exactly that.

Cutting across all four bodies is a reporting problem worth checking for in any paper you intend to rely on. Because the compound is a metal complex, the methods section needs to state which species was used, how the copper content was established, what the medium contained by way of copper, chelators and reductants, and whether a copper-salt control was run. Papers that report only a concentration in micromolar terms and a compound name have left the most important variables unspecified.

Where the GHK-Cu literature is thin or frequently misread

The recurring problem with this compound is attribution, and it appears in four distinct forms.

The first is the free-peptide versus complex ambiguity. Papers, abstracts and vendor documents use GHK and GHK-Cu interchangeably, and older work predates the convention entirely. Since the two are different chemical species with different properties, a citation that does not specify which was used, and ideally how the copper content was verified, is of limited value. When the experiment was run in serum-containing medium the distinction partly collapses anyway, because free GHK will acquire copper from the medium, but that only means the effective species was never under the experimenter's control.

The second is stoichiometry. Material sold as GHK-Cu is frequently supplied without an independent determination of copper content, and a name on a label is not a measurement. Preparations with the correct peptide and too little copper, and preparations carrying free copper salt in addition to the complex, are both consistent with a clean peptide purity figure.

The third, and the one with real experimental consequences, is copper redox chemistry. Copper cycles between the divalent and monovalent states and, in the presence of a reductant and any peroxide, participates in Fenton-type chemistry that generates hydroxyl radicals. Cell-culture medium is not a benign environment in this respect: it commonly contains ascorbate or other reductants. An excess of loosely bound copper in such a system produces oxidative stress, and oxidative stress produces transcriptional and proliferative changes that are easily read as biological activity of the compound. Coordination within the tripeptide is generally described as attenuating this behavior relative to a free copper salt, which is a good argument for the complex and a very good argument for knowing exactly how much uncomplexed copper is present.

The fourth is the over-reading of expression profiling already noted, compounded by the age-related decline claim, which is repeated with a confidence that the primary measurements do not support.

How GHK-Cu behaves in solution

GHK-Cu in solution is blue, and the color is not decorative. It arises from d-d transitions of the copper(II) center in its nitrogen-rich coordination environment, which means the color is a direct report on the coordination sphere. A correctly constituted solution is a clear blue to blue-violet. That gives you a diagnostic that no other compound in this catalog offers: if a solution of this material is colorless, the copper is no longer coordinated the way it should be, and if it is green or has drifted toward green, the coordination environment has changed, most often through displacement of a nitrogen donor by a different ligand or through partial dissociation. Faint turbidity with a colorless supernatant suggests copper has come out as an insoluble salt.

The pH dependence follows directly from the deprotonated amide nitrogen discussed above. In acidic conditions the complex dissociates, and the blue fades. Neutral to mildly alkaline conditions favor the intact complex. Strongly alkaline conditions introduce a different problem, precipitation of copper hydroxide and, in phosphate buffers, of copper phosphate. Buffer choice therefore matters more here than for a plain peptide, and buffers containing strong donor or chelating components are best avoided.

Two classes of additive are outright incompatible. Chelators, EDTA above all, have far higher affinity for copper(II) than the tripeptide does and will strip the metal quantitatively; a GHK-Cu solution in an EDTA-containing buffer is a solution of free GHK and a copper-EDTA complex. Reducing agents are the other class. Ascorbate, dithiothreitol and TCEP reduce copper(II) to copper(I), and the donor set that stabilizes the divalent ion does not stabilize the monovalent one, so the complex is destroyed and the released copper becomes redox-active. Any protocol that includes a reduction step is incompatible with keeping this material intact.

Copper complexes are also photosensitive, and light exposure can drive both ligand oxidation and metal-centered photochemistry, so amber containers and dark storage are ordinary practice.

The 100 mg quantity in this listing is much larger than the 5 to 20 mg typical elsewhere in the catalog, and the reason is straightforward: the published work uses this compound at micromolar to millimolar working concentrations rather than the nanomolar concentrations at which receptor agonists are studied, and formulation and matrix-stability work consumes material quickly. Vial size here reflects how the compound is used, not how potent it is.

Analytical notes specific to GHK-Cu

Analytical characterization of a metal complex is not the same exercise as characterization of a peptide, and the standard package is incomplete for this material in a specific and predictable way.

Mass spectrometry first. Electrospray of a coordination complex is unreliable in a way that catches people out: the complex can dissociate in the source, so the ion you observe may well be the free tripeptide rather than the copper adduct. Observing free GHK on a spectrum is therefore not evidence that the sample contained no copper, and reporting it as such is a real error that appears in supplied documentation. Gentle source conditions improve survival of the complex, and when it does survive there is a genuinely useful signature: copper has two stable isotopes, with the lighter accounting for roughly sixty-nine percent of natural abundance and the heavier roughly thirty-one percent. That produces a characteristic doublet separated by two mass units with an approximately two-to-one intensity ratio, which is unmistakable against the ordinary isotope envelope of a small peptide and is one of the few unambiguous confirmations that the metal is present in the ionized species. Note also that coordination involves loss of protons from the ligand, so the observed mass of the complex is not simply the peptide mass plus the copper mass.

Chromatography next. Reversed-phase methods for peptides typically run in acid, most often with trifluoroacetic acid, and acid dissociates this complex. A conventional purity chromatogram is therefore largely a purity chromatogram of the tripeptide, which is worth knowing but is not a measurement of the complex. Where the complex does partially survive, on-column dissociation and re-equilibration during the run produce peak splitting, shoulders and pronounced tailing, and these are chemistry rather than a bad column. Residual metal in the flow path adds further irreproducibility.

The measurement that actually settles the question is orthogonal copper quantitation. Atomic absorption spectroscopy or ICP-MS on a digested sample gives total copper independent of the peptide, and combining that with peptide content establishes stoichiometry rather than assuming it. ICP-MS has the additional benefit of reporting other metals, which is how you learn whether iron or zinc has partly displaced the copper. Ultraviolet-visible spectroscopy of the d-d absorption band is a cheap, non-destructive complement that reports on coordination rather than on total metal, and the two together are far more informative than either alone.

Compounds researchers confuse with GHK-Cu

Questions specific to GHK-Cu