GHK Chemistry: The Gly-His-Lys Tripeptide
A bench-level reference overview of free GHK, the copper-free glycyl-histidyl-lysine tripeptide: its sequence, how it is assembled by Fmoc synthesis, how it is characterized and handled, and how it differs from the copper-loaded GHK-Cu complex.
Sequence and Structure
GHK is one of the smallest peptides in the catalog: glycyl-L-histidyl-L-lysine, a three-residue chain abbreviated Gly-His-Lys. In its free form it is a simple, water-soluble, colorless molecule with a free N-terminal amine on the glycine, a histidine imidazole side chain in the middle position, and a lysine that carries a basic side-chain amine at the C-terminus. That short, well defined sequence is the entire molecule, with no bound metal, which is the distinction worth fixing in mind from the start.
The qualifier that matters here is copper-free. The same Gly-His-Lys sequence is best known as the peptide half of GHK-Cu, the copper(II) complex covered in its own GHK-Cu chemistry overview. Free GHK is the apo peptide: the starting material before any copper is loaded, characterized and stored as a peptide in its own right. For a research chemist the practical takeaway is to read this molecule as a plain tripeptide reference standard, because the chemistry of the free peptide and the chemistry of the copper-loaded complex are genuinely different. The sections below walk through the sequence detail, how it is assembled, and how its identity is confirmed.
Origin and Family: A Signaling Tripeptide
GHK belongs to the small group of short signaling peptides built around a histidine that can present donor atoms to a transition metal. Its place in the catalog is in the copper and signaling class, alongside related entries such as the alanine-histidine-lysine peptide AHK. What sets GHK apart within that family is that the very feature making it notable, the N-terminus and histidine that can grip a copper(II) ion, is in this material left unoccupied, so the free peptide is the metal-binding scaffold studied on its own.
Because the free tripeptide is the apo form of a well known metallopeptide, it is most useful to position it relative to its copper-loaded counterpart. Free GHK is what a chemist starts from; the GHK-Cu complex is what results once copper is coordinated under controlled conditions. Keeping the two distinct is the whole point of carrying a copper-free reference standard: it lets the peptide be assembled, purified, analyzed, and stored without the added variable of a bound metal, and it serves as the defined baseline against which the loaded complex is compared. Broader context on the class sits in the wider set of research overviews.
Synthesis: Fmoc Solid-Phase Assembly
Free GHK is made by Fmoc solid-phase peptide synthesis, the same strategy used across the peptide catalog, adding lysine, then histidine, then glycine to a resin one protected residue at a time. Because the chain is only three residues long, the synthesis is short and the coupling chemistry is straightforward compared with the longer sequences in the GH-axis or incretin classes. After assembly the peptide is cleaved from the resin, the side-chain protecting groups are removed, and the free Gly-His-Lys is purified to give the finished copper-free standard.
What distinguishes free GHK from its complex is what is absent: there is no copper-loading step. The route stops at the purified apo peptide rather than continuing into a separate metal-coordination stage. That makes the synthesis a single-stage exercise, and it is one reason the free peptide is a clean starting point. A chemist who wants the loaded complex takes this same purified GHK and combines it with a copper(II) source under controlled conditions, the additional step described in the GHK-Cu overview. For the copper-free reference standard, purification of the tripeptide is the final operation.
Characterization
Identity for free GHK rests on the same two complementary tools used across the reference catalog. Reversed-phase HPLC separates the target peptide from closely related impurities, such as deletion or truncation sequences, and reports the purity figure as the proportion of total peak area attributable to the intended compound. Mass spectrometry confirms identity by matching the measured mass to the expected mass for the Gly-His-Lys sequence, distinguishing the right molecule from any same-length variant.
Because this is the copper-free form, there is no copper content step in its characterization; the analysis is the peptide-only case. The point here is method rather than numbers: HPLC describes peptide purity and mass spectrometry confirms sequence identity, and a research chemist reads the two together. It is also worth noting that the free peptide presents the donor atoms that would bind a metal, so analytical handling avoids inadvertent copper or other transition-metal contact that could partially load the sample. The documentation supplied with a given standard is the reference of record for how its own identity was confirmed.
Stability and Storage
As a lyophilized solid, free GHK is comparatively stable when kept cold, dry, and out of light. Long-term storage of the dry powder is typically at freezer temperatures, with the container protected from moisture so the hygroscopic solid does not pick up water on opening. Allowing a sealed vial to reach room temperature before it is opened helps avoid condensation on the cold contents, a general handling habit that applies to GHK as much as to the rest of the catalog described in the research overviews.
Once reconstituted, the working solution is less forgiving. Peptides in solution are subject to hydrolysis, oxidation, and adsorption to surfaces, so reconstituted material is generally held cold, shielded from light, and used within a short window with freeze-thaw cycles minimized. One consideration specific to the free peptide is its metal-binding scaffold: because the N-terminus and histidine can coordinate copper and similar ions, solutions are best prepared with clean glassware and metal-free water so the sample stays the copper-free form rather than partly loading from trace contamination. These are general handling principles for a research reference standard rather than claims about any one preparation, and the documentation for a given lot should be the reference of record for its own conditions.
What GHK Is Studied For (Chemistry Only)
In a research-chemistry context, free GHK is of interest as a compact, well defined model of a metal-binding peptide in its unloaded state. It lets chemists study how a short sequence presents potential donor atoms before any metal is bound, and it serves as the apo baseline for coordination work: the copper-free reference against which the spectroscopic, chromatographic, and color changes of the loaded GHK-Cu complex are measured. As one of the simplest such peptides, it is also a clean subject for validating synthesis and analytical methods on more complex sequences.
That framing is deliberately limited to the bench. GHK supplied as a reference standard is for laboratory research use only, and nothing here describes or implies any human, cosmetic, or veterinary use or outcome. Its value to a research chemist is as a chemistry subject: a defined copper-free tripeptide whose assembly, analysis, and storage are well understood and worth knowing in detail. For the analytical side in more depth, the reference articles on characterization cover the same HPLC and mass-spectrometry methods applied across the catalog.
This overview is provided for laboratory and research use only. It is educational chemistry reference material and is not for human, cosmetic, or veterinary use. Buyers are responsible for compliance with all applicable laws and regulations.
Common questions
What is GHK?
GHK is the tripeptide glycyl-L-histidyl-L-lysine (Gly-His-Lys) in its free, copper-free form. It is a short three-residue chain with a free N-terminal amine, a histidine imidazole side chain, and a basic lysine side chain, and it is water-soluble and colorless on its own. As a research reference standard it is the apo peptide, handled as a single characterized chemical entity in the copper and signaling peptide class.
What is the difference between GHK and GHK-Cu?
GHK is the free tripeptide on its own, while GHK-Cu is that same Gly-His-Lys sequence coordinated to a copper(II) ion. Chemically they are two distinct reference standards: free GHK is a colorless peptide with no bound metal, whereas GHK-Cu is a blue metal-peptide complex with a defined 1:1 peptide-to-copper ratio. Free GHK is what you start from before any copper loading, and its handling and analysis are the peptide-only case without a copper content step.
How is GHK synthesized?
GHK is assembled by Fmoc solid-phase peptide synthesis, adding lysine, then histidine, then glycine to a resin one protected residue at a time. Because the chain is only three residues long the synthesis is short and the coupling chemistry is straightforward. The peptide is then cleaved from the resin, the side-chain protecting groups are removed, and the free tripeptide is purified. No copper-loading step is involved, since this is the copper-free form.
How should GHK be stored? (research use only)
As a lyophilized solid, GHK is kept cold, dry, and out of light, with the container protected from moisture. Reconstituted solutions are less stable and are generally held cold, used within a short window, and shielded from light, with freeze-thaw cycles minimized. Because the free peptide presents donor atoms with no bound metal, solutions can also pick up trace metal ions, so contact with copper or other transition-metal surfaces is best avoided. These are general handling principles for a research reference standard, which is for laboratory research use only and not for human or veterinary use.