GHK-Cu explained: three residues and a copper ion

GHK-Cu is the shortest peptide in this catalogue and the only one whose molecular formula contains a metal. That is exactly what makes it a special case analytically.

Gly-His-Lys, plus a copper ion

The peptide consists of three amino acids: glycine, histidine and lysine. The sequence is written Gly-His-Lys and carries the note Cu²⁺ complex in the specification table. The molecular formula C₁₄H₂₄CuN₆O₄ therefore includes the copper explicitly, and the molar mass of 403.93 g/mol takes it into account.

The histidine in the middle is the reason: its ring binds metal ions. Without this binding site there would be no complex, and GHK-Cu would simply be a tripeptide.

The CAS number 89030-95-5 refers to the complex, not to the free peptide. When checking a certificate, compare this number: the plain tripeptide without copper is a different substance with its own number.

Why copper changes the analysis

For an ordinary peptide, mass spectrometry confirms a single expected mass. Copper occurs naturally in two forms of different mass, both of them common. The spectrum therefore shows not a single signal but a pattern of two signals in a fixed ratio.

For interpretation this is more help than hindrance: the pattern is a fingerprint. If it is missing, the copper is not on the molecule, whatever the label says.

The complex can also be recognised by eye. Copper compounds of this type are coloured, so the lyophilised material is not white. For this substance, a colourless cake is a reason to look at the certificate.

Eight reports, all from the smaller vial size

The certificate library holds eight analytical reports for this substance. All eight come from 50 mg lots, while the vial sold here is 100 mg. The product page states this openly rather than assigning the reports to a different fill size: a report belongs to the lot it comes from.

All eight carry a numerical purity figure: two give 99.23%, four give above 99.8%, one gives 99.686% and one gives 99.3%. This shop states no blanket minimum purity; what counts is the measured value in the report for each lot.

The shortest molecule in the catalogue

403.93 g/mol is roughly a tenth of what retatrutide weighs. Three residues mean two coupling steps in solid-phase synthesis, so little can go wrong, and purity values are correspondingly high as a rule. That is no merit of any particular supplier; it follows from the chain length.

The real difficulty lies elsewhere: after synthesis the complex has to be formed in the first place, and the bound copper quantified. That is a step a plain peptide does not need.

Also part of two blends

GHK-Cu is contained in GLOW 70 (BPC-157, GHK-Cu and TB-500) and KLOW 80 mg (BPC-157, TB-500, GHK-Cu and KPV). For blends the specification applies per component; there is no shared purity figure for a blend. The library holds no report for GLOW 70 or KLOW 80 mg; its only blend report is for BPC-157 + TB-500, which gives no numerical purity figure. More on blends in Research blends and their certificates.

The material goes into solution with bacteriostatic water; the resulting concentration follows from the vial mass and the volume added, as described under reconstitution.

In brief

Three amino acids, one copper ion, 403.93 g/mol, CAS 89030-95-5, eight analytical reports from 50 mg lots for a 100 mg vial. Why the peptide content of a vial differs from its purity is explained in What is really in the vial.

Questions

Is GHK-Cu the same as GHK?

No. GHK-Cu is the complex of the tripeptide and a copper ion, with its own molecular formula and its own CAS number, 89030-95-5. The free tripeptide without copper is a different substance.

Why is the powder not white?

Because copper compounds of this type are coloured. For this substance the colour is part of the molecule; a colourless cake is a reason to look at the certificate of analysis.

Why are the reports for 50 mg when the product is 100 mg?

Because an analytical report belongs to the lot it comes from. The eight available reports come from 50 mg lots; the product page states this.