Quecksilber: the pathway in the body · Biomarker & Urine Analysis

Quecksilber is part of the pathway “Quecksilber”. This page shows the whole pathway; the station of Quecksilber is highlighted.

Where this laboratory value sits: Forms of mercury — vapour, salts, methyl-Hg. Mercury occurs in three forms: as vapour, which passes into the blood via the lung, as an inorganic salt, and as methylmercury, which reaches the gut with food. Each form follows its own route. Source 1

In brief

Mercury is a heavy metal that occurs as vapour, as inorganic salt and as methylmercury. In the body it binds tightly to sulfur and selenium groups of proteins and leaves via bile, stool and urine. At selenocysteine it occupies selenoenzymes.

The pathway step by step

Each station states what the compound does there. Three signs: ↑ supplies — builds up or makes available · ↓ depletes — inhibits, consumes or withholds · ↕ both, depending on amount. Behind it stands what the statement rests on: established physiology, observed in studies, or contested. The signs do not grade; they name the direction.

1. Forms of mercury → Methylmercury · L-cysteine Methylmercury is absorbed almost completely in the gut. In the body it is bound to thiols, for example to the amino acid L-cysteine. The complex then resembles an amino acid. Source 1, 2↑ supplies Bound to L-cysteine, methylmercury resembles an amino acid and is carried into cells by amino acid transporters. established physiology Source 2, 3
   ⚖ When the balance tips

   too much — If there is a lot of methylmercury in the blood, most of it is bound to thiols in the red blood cells, and more of it reaches the tissues.

   too little — If little methylmercury is present, little enters the cells via the amino acid transporters.

   established physiology · Source 1

2. Forms of mercury → Inorganic mercury Catalase Inhaled mercury vapour is oxidised to mercury ions by the enzyme catalase in the red blood cells. In blood these ions bind to thiols and proteins. Part of the vapour reaches the brain beforehand. Source 1↓ depletes Oxidation turns the membrane-crossing vapour into ions that bind to thiols and barely pass through cell membranes any more; part of the vapour reaches the brain beforehand. established physiology Source 1
   ⚖ When the balance tips

   too much — If a lot of vapour is inhaled, more of it stays unbound before oxidation and passes through membranes into the brain as well, where it then becomes ions.

   too little — If little is inhaled, the vapour is quickly oxidised to ions, which mainly reach the kidney.

   established physiology · Source 1

3. Methylmercury → Into tissues LAT1 The complex of methylmercury and L-cysteine resembles the amino acid methionine. The amino acid transporter LAT1 therefore carries it into cells, including across the blood-brain barrier. Methionine competes for the transporter. Source 3, 2↑ supplies LAT1 brings the methylmercury-cysteine complex into cells and across the blood-brain barrier, because it treats it like methionine. observed in studies Source 3, 2
   ⚖ When the balance tips

   too much — If there is a lot of the complex in the blood, it competes at LAT1 with methionine and other large amino acids.

   too little — If little of the complex is present, LAT1 carries mainly its usual amino acids.

   observed in studies · Source 3

4. Inorganic mercury → Kidney OAT1 · cysteine, glutathione The kidney absorbs mercury ions as a complex with cysteine or glutathione, among other routes via the transporter OAT1. There it binds to metallothionein. This is where it mainly accumulates. Source 4, 2↑ supplies Via transporters such as OAT1, the kidney draws mercury complexes into the cells of the renal tubules; inorganic mercury therefore accumulates mainly in the kidney. established physiology Source 4, 2
   ⚖ When the balance tips

   too much — If a lot of inorganic mercury reaches the kidney, it accumulates in the cells of the renal tubules and occupies more sulfur groups there.

   too little — If little arrives, the existing metallothionein binds most of it, and excretion in the urine stays low.

   observed in studies · Source 4

5. Into tissues → Metallothionein In tissues, methylmercury is slowly converted to mercury ions. These bind to metallothionein, a small protein with many cysteines that also binds zinc. Mercury can displace zinc in the process. Source 1, 4↓ depletes Metallothionein removes free mercury ions from the cell and binds them tightly; mercury can displace zinc from the protein in the process. observed in studies Source 1, 4
   ⚖ When the balance tips

   too much — If a lot of mercury binds to metallothionein, zinc is displaced; the released zinc prompts the formation of new metallothionein.

   too little — If little metallothionein is present, more mercury ions stay free and bind to other sulfur groups in the cell.

   observed in studies · Source 4

6. Hg on thiol groups → Selenoproteins · Selenocysteine Mercury binds even more tightly to the selenol group of selenocysteine. This amino acid sits in the active site of enzymes such as thioredoxin reductase and glutathione peroxidase. In studies, even small amounts inhibit these enzymes. Source 7, 6↓ depletes Mercury occupies the selenocysteine in the active site of thioredoxin reductase and glutathione peroxidase; in studies these enzymes are inhibited even by small amounts. observed in studies Source 7, 6
   ⚖ When the balance tips

   too much — If many selenoenzymes are occupied, peroxides and oxidised proteins are broken down more slowly in studies.

   too little — If little mercury is present, the selenocysteine stays free, and the selenoenzymes work as intended.

   observed in studies · Source 7, 6

7. Selenoproteins → Hg-selenium compound · Selenium Mercury and selenium form poorly soluble compounds. Selenium bound in this way is no longer available for building new selenoproteins. Which side prevails depends on the ratio of the amounts. Source 6↕ both, depending on amount The compound with selenium binds mercury tightly but uses up selenium; whether it mainly captures mercury or withdraws selenium depends on the ratio of the two amounts. observed in studies Source 6
   ⚖ When the balance tips

   too much — If mercury exceeds the amount of selenium, so much selenium is bound that little remains for new selenoproteins.

   too little — If there is little mercury relative to selenium, it is bound without the formation of selenoproteins stalling.

   observed in studies · Source 6

8. Hg on thiol groups → Hg-glutathione complex · Glutathione In the liver cell, mercury binds to glutathione. This complex is the form in which it can leave the cell. The glutathione leaves along with it. Source 5, 1↑ supplies Glutathione supplies the form in which mercury can leave the liver cell; it is itself exported along with it. established physiology Source 5, 1
   ⚖ When the balance tips

   too much — If a lot of mercury binds to glutathione, the liver cell loses more glutathione via the bile.

   too little — If there is little glutathione in the liver cell, less mercury is released into the bile; in animal models excretion via the bile then falls.

   observed in studies · Source 5

9. Hg-glutathione complex → Bile MRP2 The transporter MRP2 releases the glutathione complex into the bile. In this way methylmercury reaches the gut. This is the main route for methylmercury. Source 5, 1↓ depletes MRP2 removes the glutathione complex from the liver cell and releases it into the bile; this is the main route by which methylmercury leaves the body. established physiology Source 5, 1
   ⚖ When the balance tips

   too much — If a lot of the complex is released into the bile, more methylmercury reaches the gut, where part of it is absorbed again.

   too little — If MRP2 works more slowly, more mercury remains in the liver cell.

   observed in studies · Source 5, 1

10. Bile → Gut gut bacteria Gut bacteria convert part of the methylmercury into inorganic mercury, which leaves with the stool. The rest can be absorbed again. It thus circulates between liver and gut. Source 1↓ depletes Gut bacteria convert methylmercury into inorganic mercury, which the gut barely absorbs; it thus leaves the body with the stool. established physiology Source 1
    ⚖ When the balance tips

    too much — If a lot of methylmercury reaches the gut, part of it is absorbed again and circulates once more between liver and gut.

    too little — If the gut bacteria convert little of it, more methylmercury is absorbed again, and it stays in the body longer.

    observed in studies · Source 1

Further stations

• Forms of mercury — vapour, salts, methyl-Hg Mercury occurs in three forms: as vapour, which passes into the blood via the lung, as an inorganic salt, and as methylmercury, which reaches the gut with food. Each form follows its own route. Source 1↑ supplies Each form reaches the body by its own route: vapour via the lung, methylmercury via the gut, which absorbs it almost completely; only a small part of inorganic salts passes across. established physiology Source 1
  ⚖ When the balance tips

  too much — If more mercury arrives, a large part of it reaches the blood in the case of vapour and methylmercury, and a small part in the case of inorganic salts.

  too little — If little mercury arrives, correspondingly little enters the body; it has no role there.

  established physiology · Source 1

• Hg on thiol groups — SH groups of proteins Mercury binds very tightly to sulfhydryl groups (SH groups) of cysteine in proteins and in glutathione. In this way it changes the shape and activity of these proteins. Bound glutathione is then no longer available. Source 1, 7↓ depletes Mercury occupies SH groups of proteins and glutathione and holds on to them; occupied proteins change shape and activity, and bound glutathione is no longer available for other tasks. observed in studies Source 1, 7
  ⚖ When the balance tips

  too much — If a lot of mercury is bound, more proteins and more glutathione are occupied; in studies the cell's sulfur systems, such as the thioredoxin system, are thrown out of balance.

  too little — If little mercury is present, the SH groups remain mostly free for their own tasks.

  observed in studies · Source 7

Cofactors in this pathway

• Selenium — Sits as selenocysteine at the centre of selenoenzymes; mercury binds it tightly; the ratio of the amounts decides Source 6, 7In the ORY catalogue as a laboratory value: Selen
• Glutathione — Forms a complex with mercury that MRP2 exports from the cell into the bile; glutathione leaves with it Source 5, 1In the ORY catalogue as a laboratory value: Glutathion (GSH)
• L-cysteine — Forms a complex with methylmercury that LAT1 carries like an amino acid; it thus reaches cells Source 3, 2
• Methionine — The methylmercury-cysteine complex resembles methionine and uses its transporter; both compete for it Source 3In the ORY catalogue as a laboratory value: Methionin
• Zinc — Is bound, like mercury, by the cysteines of metallothionein; mercury can displace it Source 4In the ORY catalogue as a laboratory value: Zink

Sources

1. Clarkson TW, Magos L. The toxicology of mercury and its chemical compounds. Crit Rev Toxicol 2006 · PubMed 16973445
2. Bridges CC, Zalups RK. Molecular and ionic mimicry and the transport of toxic metals. Toxicol Appl Pharmacol 2005 · PubMed 15845419
3. Simmons-Willis TA, Koh AS et al. Transport of a neurotoxicant by molecular mimicry: the methylmercury-L-cysteine complex is a substrate for human L-type large neutral amino acid transporter (LAT) 1 and LAT2. Biochem J 2002 · PubMed 12117417
4. Zalups RK. Molecular interactions with mercury in the kidney. Pharmacol Rev 2000 · PubMed 10699157
5. Ballatori N, Clarkson TW. Biliary secretion of glutathione and of glutathione-metal complexes. Fundam Appl Toxicol 1985 · PubMed 4065458
6. Ralston NVC, Raymond LJ. Mercury's neurotoxicity is characterized by its disruption of selenium biochemistry. Biochim Biophys Acta Gen Subj 2018 · PubMed 29753115
7. Branco V, Carvalho C. The thioredoxin system as a target for mercury compounds. Biochim Biophys Acta Gen Subj 2019 · PubMed 30447253

Whole pathway: Quecksilber

Related pathways

• Arsen — Selen, Glutathion (GSH)
• Blei — Glutathion (GSH), Zink
• Cadmium — Glutathion (GSH), Zink
• Nickel — Glutathion (GSH), Zink

As of 2026-09-18. Draft, written by Claude to schema v2; sources checked in PubMed; expert approval pending
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