What is GHK-Cu's molecular weight?

402.92 Da for the copper complex. 340.38 Da is free GHK without the copper — a different compound.

Why is the wrong figure so widespread?

A 62 Da difference on a 400 Da molecule is 15% — large enough to matter, small enough to pass unexamined.

How do I confirm the copper is present?

The isotope pattern. Copper has two stable isotopes in a distinctive ratio, which shows directly in a mass spectrum.

GLOW (Blend)

The GHK-Cu Component

JMWritten & reviewed by Jack Muncaster · Founder, UK PeptidesLast reviewed 2026-08-234 cited sources

GHK-Cu is the copper complex at 402.92 Da, PubChem CID 71587328. Free GHK without copper is 340.38 Da, CID 73587. Quoting the free peptide's mass for the complex is a 15% error and is the most commonly repeated mistake about this compound.

Key facts

GHK-Cu complex: 402.92 Da, CID 71587328
Free GHK: 340.38 Da, CID 73587
Difference: About 15%
Sequence: Gly-His-Lys
Metal: Copper(II)
Research area: Collagen and matrix remodelling

Two compounds, two masses

GHK is a tripeptide — glycine, histidine, lysine — at 340.38 Da. GHK-Cu is that tripeptide with a copper(II) ion bound, at 402.92 Da. They are different entities with different PubChem records, and the copper is not an optional accessory: it is the reason the complex is a distinct compound.

Why the error is so common

Because the free peptide's record is easier to find and the difference is not large enough to look obviously wrong. A 62 Da gap on a 400 Da molecule is 15% — big enough to matter for any calculation, small enough to pass unexamined. This site carried the wrong figure in six places before it was corrected.

Research material referenced

GLOW 70mg — third-party HPLC tested

View — £59.99

How copper is held

The glycine-histidine-lysine motif is a recognised copper-binding arrangement, coordinating the metal through the N-terminal amine, backbone nitrogens and the histidine imidazole. The binding is specific and structural rather than incidental association, which is why the complex behaves as one compound.

What it contributes to the blend

The collagen and matrix remodelling research literature, which is the largest of the three components' and the oldest. Pickart's work spans decades, including the 2015 Biomed Research International review and the 2017 gene expression work in Brain Sciences.

And the chemistry it brings

A redox-active metal in a vial with two other peptides. That would be a problem with cysteine- or methionine-containing partners, and it is not one here because neither BPC-157 nor TB-500 contains either residue. The copper question has a clean answer for this particular combination.

Verifying it

Mass spectrometry against 402.92 Da, not 340.38. A copper complex also shows a characteristic isotope pattern, since copper has two stable isotopes in a distinctive ratio — that pattern is a direct confirmation the metal is present and bound rather than absent.

Extended research context

The GLOW (Blend) deep dive

Deep dive: the copper question, and why this particular set of partners answers it

Copper is redox-active and catalyses oxidation. In protein chemistry this is well established - trace copper accelerates thiol oxidation, disulfide scrambling and methionine oxidation, which is why chelating agents appear in so many formulation buffers. So putting a copper complex in a vial with two other peptides is a fair thing to interrogate rather than wave through. Copper attacks two residues in particular: cysteine, whose free thiol is the most readily oxidised side chain in the standard set, and methionine, whose thioether becomes the sulfoxide at plus 16 daltons. Now look at what is actually in the vial. BPC-157 is Gly-Glu-Pro-Pro-Pro-Gly-Lys-Pro-Ala-Asp-Asp-Ala-Gly-Leu-Val - no cysteine, no methionine. TB-500 is an acetylated seven-residue fragment with the same absence. The reaction copper would catalyse has no substrate present. That is a real finding rather than a reassurance, because it would not have held for many other combinations: glutathione is defined by a free thiol that oxidises in air with no catalyst at all, and IGF-1 LR3 carries three disulfide bonds whose correct pairing copper would actively disrupt. Neither belongs in a vial with GHK-Cu. This set does.

Deep dive: a blend takes the fixed ratio without the single profile

There are three ways to combine compounds and they are genuinely different propositions. Separate vials, each used independently. A blend, combined at manufacture. Or one molecule engineered to hit several targets, as retatrutide does across three receptors. The real advantage of the third is not that it hits several targets - it is that it has ONE pharmacokinetic profile. Retatrutide's three activities cannot fall out of step with each other because absorption, distribution and clearance apply to all three at once, and that is why the field pursues multi-agonism despite how hard the chemistry is. A blend buys none of that. Three peptides in one vial remain three peptides with three masses, three solubilities, three stabilities and three clearance behaviours; combining them changes the packaging, not the pharmacology. What it does cost is the ratio, which is fixed at manufacture - reconstituting in a different volume moves all three concentrations together and never their relationship. So a blend carries the inflexibility of a multi-agonist without the simplification that justifies it. What it offers instead is convenience: fewer vials, fewer reconstitutions, fewer transfers, less material lost to surfaces at each step. That is a real benefit and it is a practical one, not a pharmacological one.

Deep dive: why a blend cannot answer the question it invites

Blends invite the word synergy, so it is worth being precise about what that word means. Not that a combination works - that a combination produces MORE than its components produce independently. Two compounds each giving one unit of effect, combined giving two, is additive and entirely unremarkable. Three units would be synergy. Demonstrating it requires each component alone at the concentration present in the combination, the combination itself, and matched conditions throughout; without the individual arms there is no baseline to exceed, so a combination result on its own can never establish synergy however large it is. Here is the structural problem: those individual arms need the components separately at known concentrations, and a fixed-ratio blend whose per-component split is not stated supplies neither. The experiment that would test the claim cannot be designed from the product that prompts it. The honest position is not that synergy has been ruled out for this combination - it is that no published work addresses this combination at all, which is a different and more accurate statement. The rationale for putting these three together is overlapping research literatures in collagen, repair and cell migration, and that is a reasonable basis for a product without being evidence that the compounds interact.

Research applications

▸Combined connective tissue and matrix research protocols
▸Collagen synthesis and remodelling model systems
▸Comparative work on single compounds versus fixed combinations
▸Copper peptide coordination chemistry
▸Co-lyophilisation and multi-component formulation methodology
▸Cell migration and wound model research

Handling checklist

✓Verify GHK-Cu against 402.92 Da (CID 71587328), not 340.38 - that is free GHK
✓Verify BPC-157 against 1419.5 Da and TB-500 against 889.0 Da, not 4.9 kDa
✓Expect per-component certification - a single purity figure for a blend is a category error
✓Note the per-component mass split is not stated; no molar calculation is possible without it
✓Store lyophilised, cold, dry and protected from light - the copper complex governs
✓Reconstitute gently down the vial wall; uneven dissolution is expected and needs time, not shaking
✓Expect no disulfide or +16 Da oxidation species - no component carries cysteine or methionine

Common research-handling mistakes

Learnt from thousands of researcher orders across our UK labs.

✗ Quoting 340.38 Da for the GHK-Cu component

Fix: That is free GHK without copper, CID 73587. The complex is 402.92 Da, CID 71587328 - a 15% difference.

✗ Quoting 4.9 kDa for the TB-500 component

Fix: That is full thymosin beta-4, the 43-residue parent protein. TB-500 is a seven-residue fragment at 889.0 Da - a 5.6-fold error.

✗ Expecting a single purity figure for the blend

Fix: With three intended compounds the other two are neither impurities nor the analyte. Each component must be verified separately before blending.

✗ Shaking to help an unevenly dissolving cake

Fix: Components of different size and solubility dissolve at different rates. Shaking creates interfaces where peptides aggregate irreversibly. Swirl and wait.

✗ Reading a blend as evidence the components act together

Fix: No published work addresses this combination. The rationale is overlapping research areas, which is not evidence of interaction.

Continue researching

Peer-reviewed guides, comparators and matched reference materials.

Frequently asked questions

What is GHK-Cu's molecular weight?: 402.92 Da for the copper complex. 340.38 Da is free GHK without the copper — a different compound.
Why is the wrong figure so widespread?: A 62 Da difference on a 400 Da molecule is 15% — large enough to matter, small enough to pass unexamined.
How do I confirm the copper is present?: The isotope pattern. Copper has two stable isotopes in a distinctive ratio, which shows directly in a mass spectrum.

Primary sources & clinical trials

Peer-reviewed research and registered trials from PubMed, ClinicalTrials.gov, PubChem, FDA and NIH. All links open in a new tab and point to the primary source, so every claim can be verified at origin.

Written and reviewed by

Jack Muncaster · Founder, UK Peptides

Jack founded UK Peptides in Manchester after repeatedly receiving research compounds with missing or recycled paperwork. He is responsible for supplier selection, batch release decisions and the content published in this research library. Every article here is sourced to primary literature and every product page to a signed third-party certificate.

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