Biochemistry · Molecule
Protoporphyrin IX !
Protoporphyrin IX is the heme ring before it receives iron; it is red, fluorescent and builds up in protoporphyria.
Updated 2026-11-01
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Key facts
- It is the substrate of ferrochelatase, the last step of heme synthesis.
- It is hydrophobic: it does not appear in urine; it is excreted in bile and stool.
- It absorbs violet light (around 405 nm) and gives off red fluorescence; with light it generates reactive oxygen species.
- With zinc instead of iron it forms zinc protoporphyrin (iron deficiency, lead).
- Formula
- C₃₄H₃₄N₄O₄
- PubChem
- CID 4971
Structure
- Porphyrin ring with four methyls, two vinyls and two propionates; IX names the order of those groups, the only one nature uses.
Clinical notes
- Erythropoietic protoporphyria: high free protoporphyrin in red cells; burning pain in sunlight and risk of gallstones and liver damage.
- Fluorescence-guided surgery: oral 5-ALA makes glioma cells accumulate protoporphyrin IX and glow red.
- Photodynamic therapy: topical ALA plus light destroys actinic keratoses and some superficial skin cancers.
Pathways
Related conditions
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Test yourself
Think of the answer, then tap the question to see it.
Why does protoporphyrin not appear in urine in protoporphyria?
It is hydrophobic: it leaves through bile, so urine porphyrins are normal.
What forms when protoporphyrin IX receives zinc instead of iron?
Zinc protoporphyrin, which rises in iron deficiency and lead poisoning.
How is protoporphyrin IX used in glioma surgery?
5-ALA is given; the tumour accumulates protoporphyrin IX, which fluoresces red under violet light and marks the margins.
Molecules are shown in their neutral form, as the databases deposit them; in the cell the acids and phosphates are ionised.
Educational information, not medical advice. For any symptom, see a health professional.
Sources: Protoporphyrin IX (CID 4971) (PubChem, NCBI, 2026) · Public domain; Porphyrins blood test: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); FECH gene: MedlinePlus Genetics (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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