GHK-Cu and AHK-Cu are two copper-binding tripeptides that differ by a single residue — glycine versus alanine at position one — and that one substitution is why the published literature points them at different questions. GHK-Cu (Gly-His-Lys, copper(II) complex, CAS 89030-95-5, 403.93 g/mol) is the far more heavily studied of the pair, dominating matrix-biology and skin-model work. AHK-Cu (Ala-His-Lys, CAS 1245800-58-7, roughly 417.96 g/mol as the copper complex, INCI name copper tripeptide-3) appears almost exclusively in hair-follicle and dermal papilla research. In a GHK-Cu vs AHK-Cu comparison the practical question is not which peptide is stronger but which literature base your assay is meant to extend.
Both are supplied here as lyophilized blue powders with lot-matched HPLC certificates: GHK-Cu in 50 mg, 100 mg and 200 mg vials, and AHK-Cu in 50 mg and 100 mg vials. Both belong to the same chemical family — see the copper peptides collection — and both are research chemicals, not therapeutic products.
GHK-Cu vs AHK-Cu at a glance
| Attribute | GHK-Cu | AHK-Cu |
|---|---|---|
| Sequence | Gly-His-Lys, complexed with copper(II) | Ala-His-Lys, complexed with copper(II) |
| CAS number | 89030-95-5 | 1245800-58-7 |
| Molecular formula | C14H24N6O4·Cu | C15H26N6O4·Cu |
| Molecular weight | 403.93 g/mol (copper complex) | ≈417.96 g/mol as complex; 354.41 g/mol free tripeptide |
| Cosmetic INCI name | Copper tripeptide-1 | Copper tripeptide-3 |
| Biological origin | Identified in human plasma; matches a fragment of collagen alpha-2(I) | Synthetic analogue of the GHK motif; no established endogenous pool |
| Copper coordination | His imidazole, N-terminal amine and backbone nitrogen — a well-characterised square-planar Cu(II) site | Same His-anchored geometry; the extra methyl group at residue 1 slightly alters hydrophobicity |
| Dominant research area | Collagen and glycosaminoglycan synthesis, matrix remodelling, wound models, skin appearance | Hair follicle organ culture, dermal papilla cells, follicular angiogenic signalling |
| Depth of literature | Extensive, dating to the 1970s isolation work | Narrow, mostly 2000s cosmetic-science and follicle papers |
| Appearance in solution | Blue; colour tracks copper coordination | Blue to blue-violet; same colour indicator |
| Sizes stocked | 50 mg, 100 mg, 200 mg | 50 mg, 100 mg |
| Purity | ≥99% by HPLC, lot-matched COA | ≥99% by HPLC, lot-matched COA |
| Product page | GHK-Cu (Copper Peptide) | AHK-Cu (Copper Tripeptide-3) |
Structural difference: one methyl group, two literatures
Chemically these are near-twins. Both are tripeptides whose histidine imidazole and N-terminal amine form the primary donor set for a copper(II) ion, giving the characteristic blue complex that makes copper coordination visible without instrumentation. Replacing glycine with alanine adds a single methyl group to the first residue. That change is small enough to preserve the copper-binding geometry and large enough to alter the peptide's hydrophobicity, its surface interactions in a formulation, and — in principle — how it presents to any receptor or transporter that recognises the N-terminus.
The consequential difference is provenance rather than chemistry. GHK was identified as a naturally occurring plasma tripeptide in human research beginning in the 1970s and corresponds to a sequence found in collagen alpha-2(I), which is why so much of its literature sits in matrix biology. AHK has no comparable endogenous story; it was designed as a GHK analogue and entered the literature through cosmetic-science and hair-follicle work. If your protocol needs a molecule with a described physiological counterpart, that asymmetry matters. For background on the class, see copper peptide in the glossary and the longer treatment in What is GHK-Cu?.
What the research has examined
GHK-Cu: matrix, wound and skin models
The GHK-Cu literature is broad and mostly preclinical. Cell-culture reports have described increased collagen, elastin, decorin and glycosaminoglycan production in fibroblast systems, alongside modulation of matrix metalloproteinases and their tissue inhibitors — a remodelling profile rather than a single-target effect. Rodent and rabbit wound models published from the 1980s onward reported faster closure and altered granulation tissue in copper-tripeptide-treated groups compared with vehicle. Gene-expression profiling work has reported that GHK influences a large number of transcripts in cultured cells, which is why reviews often describe it as a matrix signalling molecule rather than a receptor agonist. Human data exist chiefly for cosmetic formulations, where controlled facial studies of GHK-containing creams reported measurable changes in skin roughness and density readouts; those are appearance endpoints in finished cosmetic products, not claims about research-grade powder.
AHK-Cu: hair follicle and dermal papilla systems
AHK-Cu shows up in a much narrower slice of the literature. Published work using human hair follicle organ culture has reported prolonged follicle elongation and delayed transition out of the growth phase relative to control media, and dermal papilla cell studies have reported increased proliferation and elevated VEGF expression. The proposed reading in those papers is follicular angiogenic and papilla-support signalling. The evidence base is thinner, the model systems are more specialised, and independent replication is limited — all of which should be stated plainly in any protocol that builds on it. Our fuller write-up sits at What is AHK-Cu?, and the broader field is mapped in Peptides for Hair Growth: Research Overview.
Where the two overlap
Both peptides are studied as copper carriers, and a recurring methodological problem in the field is separating peptide-specific signalling from the effects of delivering bioavailable copper. Copper alone influences lysyl oxidase activity and several redox-sensitive pathways. Well-designed comparisons therefore include a copper-salt control and a copper-free peptide control; without them, a positive result cannot distinguish the tripeptide from its cargo. This applies equally to GHK-Cu and AHK-Cu and is the single most common weakness in copper-peptide experiments.
Which to choose for which research question
- Collagen, elastin or extracellular-matrix endpoints in fibroblast or dermal models: GHK-Cu, because the comparison literature and the assay conventions already exist there. Start with GHK-Cu vials.
- Hair follicle organ culture, dermal papilla proliferation or follicular angiogenesis readouts: AHK-Cu is the peptide the existing follicle papers used; AHK-Cu vials keep your work comparable to that literature.
- Head-to-head analogue studies: run both at matched molarity rather than matched mass — the 14 g/mol difference is small but the free-peptide and complex weights are not interchangeable. The molecular weight and molarity guide covers the arithmetic.
- Topical formulation science: both are used, and the pre-formulated GHK-Cu + AHK-Cu Hair Serum exists for work on finished-format stability rather than raw peptide chemistry.
- Multi-peptide follicle panels: the Hair Growth Stack pairs both copper tripeptides with PTD-DBM for comparative screening designs.
Handling, stability and storage differences
Handling is nearly identical, with one shared caution that matters more than any difference between them: the copper complex is the active species in both cases, and strongly acidic media can dissociate it. A solution that loses its blue colour has told you something about its integrity. Both peptides dissolve readily in bacteriostatic or sterile water; both are stored lyophilized at −20 °C, sealed and protected from light and moisture; and reconstituted stocks are held at 2–8 °C, protected from light, and used within the study window. Repeated freeze–thaw of aqueous stocks is the usual cause of unexplained potency drift, so aliquoting on first reconstitution is standard practice. Practical detail lives in How to Store Peptides and the reconstitution guide.
One formulation note specific to topical research: copper tripeptides are chemically incompatible with several common cosmetic actives — strong reducing agents and high-concentration acids in particular — and combining them in a single vehicle can strip the copper before the peptide reaches the model system. Formulation-side considerations are discussed in Topical Peptides in Cosmetic Research.
Purity, COA and what to verify
For copper peptides a purity figure alone is incomplete. The certificate should confirm peptide identity by mass spectrometry, HPLC purity of the peptide component, and ideally copper content or the complex stoichiometry, because a nominally pure tripeptide that is only partially complexed will behave differently in a copper-sensitive assay. Both products here are supplied at ≥99% HPLC purity with a lot-matched certificate; how to read one is covered in How to Read a Peptide COA. Lot-to-lot consistency matters most in longitudinal work, so record lot numbers alongside your results.
Summary for protocol selection
GHK-Cu is the reference copper tripeptide: deeper literature, an identified endogenous counterpart, and the standard choice for matrix and skin-model research. AHK-Cu is the narrower, follicle-oriented analogue, appropriate when you are extending hair-research findings specifically. Neither should be described in therapeutic terms, and neither is intended for human or veterinary use. Related comparisons and family context are available across the hair research peptides collection and the skin research overview.