These Side Notes go deeper into how two copper-dependent enzymes take part in producing chemical messengers in the nervous system, with tables on the reference value and food sources, plus the full wording of the authorized EU claim.
Not every messenger of the nervous system is ready for use the moment it leaves a cell. Small molecules such as dopamine or serotonin already exist in their working form as soon as they're formed. Neuropeptides — messengers that are themselves made of a short chain of amino acids — take a longer detour instead: they first form as part of a larger precursor protein, out of which several cuts and chemical changes eventually separate the finished molecule.
One of these final steps concerns a glycine at the end of the chain, which for many neuropeptides has to be removed and converted into an amide group before the molecule can act at its receptor. These Side Notes trace exactly that one step — and the metal without which it doesn't happen.
It starts with a gene that codes for a long precursor protein, the so-called prepropeptide. Specialized enzymes cut several shorter segments out of it. Some of these segments carry an extra glycine at the end that serves as a signal for the next processing step.
The enzyme peptidylglycine alpha-amidating monooxygenase is made up of two parts that work one after the other. Both sit in the same storage vesicles as the maturing peptide itself.
The PHM subunit carries two spatially separate copper ions. With oxygen and ascorbic acid as helper substances, they add a hydroxyl group to the terminal glycine.
The neighboring PAL subunit doesn't itself need copper. It splits off the hydroxylated glycine as glyoxylate and leaves the finished amide group on the peptide.
Only with this amide group does the molecule fit into the binding pocket of many receptors. Without the previous step, the effect wouldn't occur, no matter how much precursor protein the cell provides.
“Copper contributes to normal functioning of the nervous system”
EU-authorized wording · Regulation (EU) No 432/2012
A second enzyme with a comparable structure, dopamine beta-hydroxylase, occurs in certain nerve cells and converts one messenger into another there. Both enzymes belong to the same family of copper-dependent monooxygenases and are included here purely for scientific context, not as part of the official wording itself.
1,000 micrograms of copper a day: that's the figure EU food labeling sets as the reference value for adults, regardless of any one person's individual need. The table below shows rounded approximate values for a few foods; origin and preparation shift the actual amount.
| Food | Copper (mg per 100 g) |
|---|---|
| Beef liver, cooked | approx. 10 |
| Cocoa powder, unsweetened | approx. 3.8 |
| Sesame seeds | approx. 4.1 |
| Cashews | approx. 2.2 |
| Shiitake mushrooms, dried | approx. 5.0 |
| Lentils, cooked | approx. 0.25 |
| Whole-wheat pasta, cooked | approx. 0.15 |
Copper is absorbed mainly in the upper small intestine. At very high single doses from supplements, zinc and copper can affect each other's absorption, since both partly use the same channels in the intestinal lining. With an ordinary mixed diet, and at amounts in line with the respective reference values, taking both together is considered unproblematic.
The official sentence is deliberately kept short and names neither PAM nor dopamine beta-hydroxylase specifically. Both enzymes belong to the scientific background against which EFSA reviewed the claim — they aren't themselves part of the wording, and are mentioned here only to provide context.
The word “normal” refers to the physiologically ordinary course of events with an otherwise adequate copper supply — not to any increase beyond that, and not to an existing condition that needs medical assessment. The claim, moreover, may only be used for foods that qualify as at least a source of copper under Regulation (EC) No 1924/2006, and it refers exclusively to copper — not to any other ingredient in a product.
“Copper contributes to normal functioning of the nervous system” — EU-authorized wording · Regulation (EU) No 432/2012. One sentence, two enzymes in the scientific background, no statement beyond that.
No. The scientific literature describes a second, related enzyme with a similar dependence on copper, dopamine beta-hydroxylase. Beyond that, copper has further EU claims, each independently reviewed, covering other subject areas that this text doesn't go into.
It doesn't. The claim captures a normal process that already takes place given an adequate supply — not an increase in that process from a higher intake than usual.
For peptidylglycine alpha-amidating monooxygenase. The name describes what the enzyme does: it converts a glycine-containing precursor end into an amide group.
With a varied selection of foods like the ones shown in the table above, the reference value is usually covered through daily meals alone. With a one-sided diet or an existing medical condition, an individual assessment by a qualified professional is a good idea.
No, explicitly not. This text places scientific background in context and can never replace a personal assessment by a doctor.
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