AHK-Cu

AHK-Cu, also designated copper tripeptide-3, is the copper(II) complex of alanyl-L-histidyl-L-lysine. The metal is held in an approximately square-planar coordination sphere built from the imidazole nitrogen of histidine, the N-terminal amine, and a deprotonated backbone amide nitrogen, with the remaining site occupied by water or a buffer component. The lysine side chain sits outside the coordination sphere and carries a positive charge across the usual working pH range.

It differs from the more widely studied GHK-Cu at a single position: alanine replaces glycine at residue one, adding a methyl group adjacent to the coordinating amine. That one substitution changes the steric environment of the metal and the stability constant of the complex, which is why the two are studied as separate entities rather than treated as interchangeable copper carriers.

The functional unit is the complex rather than either component alone. The peptide acts as a chelating ligand that holds copper in a defined coordination environment, and the coordination chemistry, not the sequence, is what most of the reported activity depends on.

Cultured dermal papilla cells and fibroblast monolayers make up the bulk of the in vitro literature, with reported endpoints covering proliferation, extracellular matrix protein deposition, and expression of collagen and elastin genes. Rodent follicle preparations extend the same work into an in vivo system.

Copper-dependent enzymology is the mechanistic thread that runs through this literature. Lysyl oxidase, which catalyses the cross-linking of collagen and elastin, and superoxide dismutase both require copper at the active site, so any compound that alters copper availability inside a cell has a plausible route to matrix and redox endpoints. Comparative work against GHK-Cu is common, and the two complexes do not behave identically in the same assay.

A peptide-only Certificate of Analysis does not fully describe this material. Reversed-phase HPLC and mass spectrometry confirm the Ala-His-Lys sequence and its purity, but neither speaks to the copper. Metal content is established separately, by inductively coupled plasma mass spectrometry or atomic absorption, and the ratio of copper to peptide is the number that says whether the complex is fully formed.

Ultraviolet-visible spectroscopy is the fastest confirmation available at the bench. The complex carries a broad copper d-d absorption in the region of 600 to 640 nanometres, and it is the origin of the characteristic deep blue colour. Material that dissolves to a pale or colourless solution has not formed the complex, whatever the peptide purity figure says.