GHK, GHK-Cu and AHK-Cu often get listed side by side, like three spellings of one thing. They're a letter or two apart, after all. But search PubMed for the exact name "GHK-Cu" and you get 83 papers. "AHK-Cu" gets one. Same thing? Nope.
GHK, GHK-Cu and AHK-Cu are three different molecules
A peptide is a short chain of amino acids, the building blocks of protein. GHK has three: glycine, histidine and lysine. GHK-Cu is that same chain holding one copper ion. AHK-Cu swaps the first link, glycine, for alanine, and holds copper too. One swap, one metal. On a certificate, that's three different weights.
The proof: one swapped link and one copper coin
Here's what's actually going on.
Start with the chain. Alanine is glycine plus one extra carbon and two hydrogens. Swap it in at the front and GHK becomes AHK, 14 daltons heavier. A dalton is the unit chemists weigh molecules in. Here's how PubChem, the U.S. government's chemistry database, lists all four:
| Sequence | Formula | Weight (g/mol) | |
|---|---|---|---|
| GHK | Gly-His-Lys | C14H24N6O4 | 340.38 |
| GHK-Cu | GHK + one copper | C14H22CuN6O4 | 401.91 |
| AHK | Ala-His-Lys | C15H26N6O4 | 354.41 |
| AHK-Cu | AHK + one copper, filed as a hydrochloride salt | C15H24ClCuN6O4 (charge -1) | 451.39 |
Copper sits in a three-finger grip. In 2011, a CNRS team led from Toulouse used X-ray crystallography and a stack of other methods to study how GHK holds copper. In solution, they confirmed, three nitrogen atoms do the holding: one at the start of the chain, one in its backbone, one on histidine's ring (Hureau et al., Chemistry 2011). Picture a coin pinched between a thumb and two fingers. One GHK holds one copper (Freedman et al., Biochemistry 1982).
AHK fits the same pattern. Chemists call it the Xxx-His motif: any amino acid, then histidine, at the front of a chain. A 2017 Strasbourg-led paper names GHK as one of two textbook examples of this copper grip (Gonzalez et al., Inorg Chem 2017). In AHK, alanine just fills the "any" slot.
What copper adds: about 62 daltons and a color. Copper weighs 63.55. GHK gives up two hydrogens to make room for it (Freedman's team measured them leaving), so GHK-Cu lands near 402, not 404. Copper is also where the blue comes from.
So why should you care? Weight is how a vial proves its name. LC-MS identity testing confirms a molecule by its weight. GHK and AHK sit 14 daltons apart, so identity has to land on the right one. Color can't make that call.
"Why does AHK-Cu weigh 451?" Fair catch. PubChem files it as a hydrochloride salt, so its formula carries an extra chlorine, about 35 daltons on its own. Before you compare two weights, check they describe the same form.
The big learning lesson
Keep reading: What is GHK-Cu? The copper peptide, explained · How to read a peptide certificate of analysis · TB-500 vs thymosin beta-4
Frequently asked questions
Is GHK the same as GHK-Cu?
Same chain, different molecule. GHK-Cu is GHK holding one copper ion, which makes it about 62 daltons heavier and gives it its blue color.
What's the difference between GHK-Cu and AHK-Cu?
The first amino acid. GHK-Cu starts with glycine, AHK-Cu with alanine, which adds one carbon and two hydrogens. GHK-Cu also has a far bigger published record: 83 PubMed papers by name, against one for AHK-Cu.
Why do GHK-Cu molecular weights differ between sources?
Copper complexes can be recorded with different charges or as salts. PubChem itself lists GHK-Cu at 401.91 in one record and 402.92 in another, so check which form a number refers to.