Amazonitblick · Mg 12 · K 19
Scientific facts on two minerals — in line with EU Regulation (EU) No 432/2012
To the detailed sectionSkeletal muscle is the largest human tissue by mass. In an adult it makes up roughly forty per cent of total mass, depending on build and level of use. That alone makes it stand out in any mineral balance: where there is a great deal of tissue, there is also a large share of whatever is built into tissue.
In the case of magnesium, about a quarter of the body's stock of some 24 grams sits in the musculature; the larger share is in the skeleton. For potassium the ratio is more pronounced. Of the roughly 3,500 millimoles an adult carries, about three quarters lie in the musculature — no other tissue comes close.
What appears on this domain is drawn from the biochemical and nutritional science literature. The two wordings authorised in the European Union are set apart from it: they appear verbatim, in boxes of their own, and each of them belongs to exactly one element.
The two elements appear at different points in the muscle fibre and do different things there. Magnesium is part of the substrate that a whole class of enzymes works on. Potassium sits alongside and makes an enzyme functional in the first place, without itself being converted. Both processes can be described separately, and that is exactly how the entries in the European register are structured.
The myosin head splits adenosine triphosphate and draws from it the energy for its working stroke. What it binds is, strictly speaking, not ATP but the complex of ATP and a doubly positive magnesium ion. The ion attaches to the beta and gamma phosphate groups, shields their negative charge and holds the molecule in the geometry the enzyme expects. Free, uncomplexed ATP is turned over by myosin ATPase only very slowly.
The same applies to the kinases of sugar breakdown, to the calcium pump of the sarcoplasmic reticulum and to creatine kinase. All of these enzymes work on the magnesium complex and not on the bare nucleotide. It is this relationship that the entry authorised by the European Union for magnesium refers to:
Under Regulation (EU) No 432/2012
At the end of glycolysis stands pyruvate kinase. It transfers a phosphate group from phosphoenolpyruvate to ADP, producing pyruvate and ATP. This enzyme belongs to a small group that requires a monovalent cation in addition to the divalent ion. In animal tissue that is potassium. It occupies a binding pocket of its own directly next to the active site and aligns the substrate so that the transfer can take place at all.
Potassium is not consumed in this reaction. It sits in place as long as the concentration inside the cell is right, and is needed again at the next turnover. For this element the register carries a line of its own, which must be read independently of the previous one:
Under Regulation (EU) No 432/2012
The two lines quoted come from the annex to Regulation (EU) No 432/2012. There they are each assigned to a single nutrient and may not be drawn together into a joint statement. A product may carry such a line only if it contains a significant amount of the mineral in question within the meaning of nutrition labelling.
Everything else on this page is editorial text on biochemistry. It describes processes documented in the specialist literature and is deliberately not presented as an authorised claim. Statements about diseases, their prevention or their course appear neither in the quoted lines nor in the explanatory text.
Each of the two authorised wordings is tied to a single element. That is why each element stands here on its own, with its own figures and its own line.
Inside the cell by far the greater part of the magnesium is not free but bound to nucleotides, to creatine phosphate and to proteins. The free concentration in the cytosol runs to roughly 0.5 to 1 millimole per litre, while a muscle sample as a whole shows around eight to ten millimoles per kilogram of wet tissue. These two figures therefore do not measure the same thing.
In food the element is found above all in seeds, nuts, pulses and wholegrain products; mineral waters contribute to very different degrees depending on the source. The labelling reference value under Annex XIII is 375 milligrams per day.
Under Regulation (EU) No 432/2012
Potassium is the most abundant cation inside the cell. In muscle, about 90 to 100 millimoles are measured per kilogram of wet tissue; in blood plasma the value is two orders of magnitude lower. The element is taken up from potatoes, pulses, vegetables, fruit and dried fruit.
The labelling reference value under Annex XIII is 2,000 milligrams per day.
Under Regulation (EU) No 432/2012
The two daily amounts — 375 and 2,000 milligrams — appear in Annex XIII of Regulation (EU) No 1169/2011 and serve nutrition labelling. They do not belong to the lines quoted above and say nothing about what amount would be appropriate for any individual person.
The two sets of rules only come together when a product is to carry a claim: the reference amount from 1169/2011 determines the content above which the sentence from 432/2012 may be used at all.
This page gives the short form. The complete edition sets out the enzyme list, the content ranges of both elements and the derivation of the labelling figures.
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