Blei: the pathway in the body

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

Where this laboratory value sits: Lead in food and air — via gut and lung. Lead reaches the gut with food and drinking water, or the lung as fine dust. From the lung it passes quickly into the blood. Source 1, 2

In brief

Lead is a heavy metal with no known role in the body. It enters via gut and lung, is carried in the erythrocytes, stored in bone in place of calcium, and inhibits enzymes of haem formation.

The pathway step by step

1. Lead in food and air → Into the gut cell DMT1 In the gut, lead uses transport routes of other metals: the iron transporter DMT1 and uptake routes for calcium. This is called ionic mimicry. Source 1
2. Into the gut cell → Lead in blood In blood, lead sits almost entirely in the red blood cells (erythrocytes), mainly bound to the enzyme ALAD. Only a small part moves freely in plasma. Source 2
3. Lead in blood → Bone · instead of calcium Lead is built into bone mineral in place of calcium. Bone is the largest store; during bone remodelling it slowly releases lead back into the blood. Source 3, 2
4. Lead in blood → Kidney From plasma, lead reaches soft tissues such as kidney and liver and binds to metallothionein there. It leaves the body mainly with the urine, a small part via the bile. Source 2, 7
5. 5-Aminolevulinic acid → Porphobilinogen ALAD · Zinc ALA dehydratase (ALAD) joins two molecules of ALA into porphobilinogen. Lead inhibits exactly this step; ALA is then not converted further. Source 4, 8
6. Porphobilinogen → Protoporphyrin IX several enzymes Several enzymes build the ring protoporphyrin IX from porphobilinogen. The last steps run in the mitochondrion. Source 8
7. Protoporphyrin IX → Haem Ferrochelatase · Iron Ferrochelatase inserts iron into protoporphyrin IX; this forms haem, the pigment of haemoglobin. Lead also inhibits this enzyme. Source 8, 4
8. Protoporphyrin IX → Zinc protoporphyrin Ferrochelatase · Zinc When ferrochelatase does not work with iron, it inserts zinc into protoporphyrin IX. This forms zinc protoporphyrin, which stays in the red blood cells. Source 5

Cofactors in this pathway

• Zinc — Cofactor of ALAD; lead takes its place in the active site Source 4, 8In the ORY catalogue as a laboratory value: Zink
• Iron — Ferrochelatase inserts iron into protoporphyrin IX; lead inhibits this step Source 8, 5In the ORY catalogue as a laboratory value: Eisen
• Glutathione — Binds lead via its SH group inside the cell Source 6In the ORY catalogue as a laboratory value: Glutathion (GSH)
• Calcium — Lead uses uptake routes for calcium and takes its place in bone Source 1, 3In the ORY catalogue as a laboratory value: Calcium (intrazellulär)
• Vitamin B6 — Cofactor of ALA synthase, which joins succinyl-CoA and glycine to form ALA Source 8In the ORY catalogue as a laboratory value: Vitamin B6
• Glycine — Building block of 5-aminolevulinic acid, the first precursor of haem Source 8In the ORY catalogue as a laboratory value: Glycin

Sources

1. Bridges CC, Zalups RK. Molecular and ionic mimicry and the transport of toxic metals. Toxicol Appl Pharmacol 2005 · PubMed 15845419
2. Barbosa F Jr, Tanus-Santos JE et al. A critical review of biomarkers used for monitoring human exposure to lead: advantages, limitations, and future needs. Environ Health Perspect 2005 · PubMed 16330345
3. Rabinowitz MB. Toxicokinetics of bone lead. Environ Health Perspect 1991 · PubMed 2040248
4. Warren MJ, Cooper JB et al. Lead poisoning, haem synthesis and 5-aminolaevulinic acid dehydratase. Trends Biochem Sci 1998 · PubMed 9644976
5. Labbé RF, Vreman HJ et al. Zinc protoporphyrin: A metabolite with a mission. Clin Chem 1999 · PubMed 10585337
6. Ahamed M, Siddiqui MK. Low level lead exposure and oxidative stress: current opinions. Clin Chim Acta 2007 · PubMed 17573057
7. Wong DL, Merrifield-MacRae ME et al. Lead(II) Binding in Metallothioneins. Met Ions Life Sci 2017 · PubMed 28731302
8. Ajioka RS, Phillips JD et al. Biosynthesis of heme in mammals. Biochim Biophys Acta 2006 · PubMed 16839620

Whole pathway: Blei

Related pathways

• Cadmium — Zink, Eisen
• Nickel — Zink, Eisen
• Quecksilber — Zink, Glutathion (GSH)

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