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[Biochemistry](https://durgical.com/en/biochemistry/) · Topic

# Magnesium

Magnesium partners ATP in almost every energy-using reaction and steadies nerves and muscles, including the heart.

Updated 2026-11-01

## Key facts

- The real form of ATP in the cell is the Mg-ATP complex: all kinases (hexokinase, PFK-1) need magnesium.
- More than half is in bone and nearly all the rest inside cells; serum magnesium reflects stores poorly.
- Low magnesium causes hypocalcaemia (blocks PTH) and hypokalaemia (the kidney wastes potassium) that do not correct until it is replaced.
- Magnesium sulphate prevents eclamptic seizures and treats polymorphic ventricular tachycardia (torsades de pointes).

## In detail

- Sources: green leaves (chlorophyll has magnesium at its centre), nuts, seeds, legumes, whole grains, cocoa.
- Roles: cofactor of more than 300 enzymes (all that use ATP, DNA and protein synthesis), membrane stabiliser, physiological blocker of the NMDA receptor and of calcium channels.
- Balance: absorbed in the small intestine and regulated by the kidney, mainly in the thick ascending limb of Henle.
- Causes of deficiency: chronic diarrhoea, alcoholism, loop and thiazide diuretics, long-term proton pump inhibitors, poorly controlled diabetes, refeeding syndrome.
- Hypomagnesaemia: tremor, tetany, seizures, arrhythmias (long QT, torsades).
- Hypermagnesaemia (almost always kidney failure plus laxatives or an infusion): loss of tendon reflexes (first sign), hypotension, respiratory depression, cardiac arrest.
- Lab: serum magnesium; urine magnesium to tell renal from gut losses.

**Also called**
Mg²⁺

## Clinical notes

- During magnesium sulphate infusion for preeclampsia, knee reflexes, breathing and urine output are watched; the antidote is calcium gluconate.
- Transketolase and thiamine pyrophosphokinase need magnesium: in Wernicke encephalopathy magnesium is corrected together with thiamine.
- People with alcoholism often lack magnesium, potassium, phosphate and thiamine at the same time.

## Pathways

- [Glycolysis](https://durgical.com/en/biochemistry/pathways/glycolysis/)

## Related conditions

- [Preeclampsia](https://durgical.com/en/conditions/preeclampsia/)
- [Wernicke encephalopathy (thiamine deficiency)](https://durgical.com/en/conditions/wernicke-encephalopathy/)
- [Atrial fibrillation](https://durgical.com/en/conditions/atrial-fibrillation/)

## Related

- [ATP (adenosine triphosphate)](https://durgical.com/en/biochemistry/molecules/atp/)
- [Na⁺/K⁺-ATPase (sodium pump)](https://durgical.com/en/biochemistry/enzymes/na-k-atpase/)
- [Calcium and phosphate](https://durgical.com/en/biochemistry/topics/calcium-and-phosphate/)
- [Thiamine (vitamin B1)](https://durgical.com/en/biochemistry/molecules/thiamine/)
- [Hexokinase](https://durgical.com/en/biochemistry/enzymes/hexokinase/)

## Test yourself

Think of the answer, then tap the question to see it.

## Why do kinases need magnesium?

The true substrate is the Mg-ATP complex: magnesium neutralises phosphate charges and positions ATP in the active site.

## Why does hypokalaemia not correct when magnesium is low?

Without magnesium the kidney's ROMK channels open more and potassium keeps leaking into urine.

## What is the first sign of magnesium toxicity?

Loss of deep tendon reflexes, before respiratory depression and cardiac arrest.

## What is magnesium sulphate used for in obstetrics?

To prevent and treat the seizures of severe preeclampsia and eclampsia.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Magnesium in diet: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/002423.htm) (MedlinePlus, US National Library of Medicine, 2026); [Magnesium Blood Test: MedlinePlus Medical Test](https://medlineplus.gov/lab-tests/magnesium-blood-test/) (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

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