Inside the cell, magnesium hardly ever occurs as a single particle. By far the largest part sits on the phosphate groups of nucleotides, and this pairing is the reason the ion turns up again and again in accounts of how signals are handled. The sections below follow that up: first the way into the fluid around nerve tissue, then two places where the pairing has been measured closely, and last the reach of the official sentence.
The fluid that surrounds the brain and the spinal cord is made, not let through. Answerable for it is a tissue with a heavy blood flow in the cavities of the brain, the choroid plexus. Its covering layer is shut tight where the cells meet, so that the gap between two neighboring cells drops out as a way through. What remains is the route straight across the cell interior — in on the blood side, out on the fluid side, over membrane proteins of its own in each case.
The outcome of this build can be put in numbers. The unbound share of the magnesium lies higher in the fluid than in blood plasma, and it does not come down to the same degree when the plasma figure moves downward inside its customary range. Review articles describe this behavior as a compartment held on its own books.
| Compartment | in total | free share |
|---|---|---|
| Blood plasma | 0.75 – 0.95 | 0.50 – 0.60 |
| Cerebrospinal fluid | 1.00 – 1.20 | 0.80 – 0.90 |
| Cell water, in general | 17 – 20 | 0.50 – 1.00 |
The ranges come from physiological review articles and shift with the measuring method. They describe orders of magnitude and are neither an intake amount nor a value for any one person. Not one of these numbers occurs in the text of Regulation (EU) No 432/2012.
The third row of the table shows a wide gap between the total amount and the unbound share. The rest has not gone missing; it is tied up. The binding partners are above all nucleotides: molecules with a chain of two or three phosphate groups whose oxygen atoms carry negative charge. A doubly positive ion settles there and offsets part of that charge.
Out of this preference follows a rule that textbooks rarely set out in large letters: wherever a cell is said to hold a nucleotide with three phosphate groups, what is practically always meant is the pair of nucleotide and magnesium ion. The free form makes up only a small share of it. Enzymes that take such molecules in are fitted accordingly to the pair and not to the nucleotide on its own.
When the literature writes a sequence out step by step, the ion therefore shows up at places where one would not look for it. It is not the leading figure but the still part of a mounting: it holds the phosphate chain in a particular position so that an enzyme finds it in the right orientation. The two sections that follow show this with two examples from nerve tissue.
Many receiving posts on the membrane of a nerve cell do not pass on by themselves what they take in. They sit on top of a protein made of three parts; the largest of them carries a pocket for a nucleotide. What is lodged in that pocket decides whether the protein rests or works — and the magnesium ion is there at every exchange.
The pocket itself is built from a loop that occurs in the very same shape across a great many proteins of this kind. It lays itself around the phosphate chain of the nucleotide. One single building block of this loop, a serine or a threonine residue, reaches for the ion together with oxygen atoms of the second and the third phosphate group and holds it fast in the middle. As soon as the third phosphate group is split off, one of these holding points falls away and the bond loosens.
| Step | At the nucleotide | At the ion |
|---|---|---|
| Resting position | two phosphate groups in the pocket | loosely bound, easily shed |
| Receiving post takes a signal in | the pocket opens, the nucleotide leaves it | not bound |
| Fresh supply enters | a nucleotide with three phosphate groups settles in | held firmly between loop and phosphate chain |
| Splitting off | the third phosphate group is severed | loses one holding point |
| Return to the resting position | two phosphate groups stay behind | loosely bound once more |
A simplified account after work in structural biology. The order of steps serves clarity; it is no part of the authorized wording and grounds no claim about a food.
The second example follows straight on from the first. When the subunit from the previous section passes something along, it meets an enzyme anchored in the membrane and made of two halves. Only once these two halves move together does a cleft arise between them in which something can happen.
Two seats for doubly charged metal ions lie close beside each other in this cleft. The one seat lines up a hydroxyl group of the sugar part so that it can attack the molecule’s own phosphate chain. The other takes hold of the piece that comes off in the process and keeps it there until it leaves the cleft. What stays behind is a molecule closed into a ring, which travels on inside the cell as a messenger.
That an enzyme keeps two metal seats at once is no special case of this one protein. It is a pattern described for many enzymes that work on phosphate chains. Crystal structures show the two seats a few tenths of a nanometer apart, and trials with altered building blocks of the cleft give each seat a different job. Which metal actually sits there in living tissue depends on which one is to be had in dissolved form; under the usual conditions of a cell that is overwhelmingly magnesium.
Up to here everything was physiology literature: a tissue, a covering layer, a pocket, a cleft, two metal seats. The part usable in law, by contrast, turns out very short. Before a health claim may be used across the Union, it goes through a scientific assessment at Union level; the wording settled there is then entered into a register and holds unaltered from that point on. From that moment the text is fixed.
“Magnesium contributes to normal functioning of the nervous system”
EU-authorized wording · Regulation (EU) No 432/2012, entry 242 of the Union list.
The sentence is tied to a condition: it may stand only where a product reaches the minimum amount laid down in the EU labeling rules. Whatever else a product holds is untouched by that.
Named are a mineral, a body system and the word normal. Not named are an amount, an organ, a tissue, an age, a cell layer, an enzyme and a span of time. Neither choroid plexus nor covering layer, neither the pocket of the subunit nor the cleft with the two metal seats occurs in it. These terms stand here because they show on what occasion the field went into the connection.
It denotes the course of things as physiology describes it in adults with no particular history, and it draws a ceiling over the statement. Nothing above and beyond that is being said. Nor does the line speak of a condition that would first have to be brought about. It is addressed to adults at large, women as well as men; no distinction is drawn there by hair color, body weight or way of living.
Because the distance between two fluid compartments is what can be set out cleanly on this subject. A table of foods with numbers beside them would suggest that something can be worked out from it. Soil, variety and preparation shift such values more, though, than a column is able to show.
No. This fluid is obtained through a puncture, and that is done for medical reasons of an entirely different kind, not to appraise a diet. The numbers in the first table come from published measurement series and give orders of magnitude, not values for any one person.
Because mechanism and amount are two separate levels. The literature describes at which spot of a protein an ion sits; it derives no intake from that. The authorized sentence in turn names no number and ties the statement to no single protein. Anyone who wants to know how their own diet stands settles that in a consultation that can ask questions and can measure.
No. The wording is filed in the Union list and holds in exactly that version. Any widening — an organ, a tissue, a fluid, a number — counts in law as a new assertion and is therefore not allowed. An editorial text such as this one may carry the term, by contrast, as long as it stands beside the sentence and not inside it.
The five sections above stand there unabridged, rounded out by the measurement series behind the two tables, a list of the review articles drawn on, and the register entry together with its identifier and its source reference.
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