Protoporphyrinogen oxidase

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Available structures
PDBOrtholog search: PDBe RCSB
AliasesPPOX, PPO, V290M, VP, protoporphyrinogen oxidase
External IDsOMIM: 600923 MGI: 104968 HomoloGene: 262 GeneCards: PPOX
Gene location (Human)
Chromosome 1 (human)
Chr.Chromosome 1 (human)[1]
Chromosome 1 (human)
Genomic location for PPOX
Genomic location for PPOX
Band1q23.3Start161,166,056 bp[1]
End161,178,013 bp[1]
RNA expression pattern
PBB GE PPOX 204788 s at fs.png
More reference expression data
RefSeq (mRNA)


RefSeq (protein)


Location (UCSC)Chr 1: 161.17 – 161.18 MbChr 1: 171.28 – 171.28 Mb
PubMed search[3][4]
View/Edit HumanView/Edit Mouse
protoporphyrinogen oxidase
Heme synthesis.png
Heme synthesis—note that some reactions occur in the cytoplasm and some in the mitochondrion (yellow)
EC number1.3.3.4
CAS number53986-32-6
IntEnzIntEnz view
ExPASyNiceZyme view
MetaCycmetabolic pathway
PDB structuresRCSB PDB PDBe PDBsum
Gene OntologyAmiGO / QuickGO

Protoporphyrinogen oxidase is an enzyme that in humans is encoded by the PPOX gene.[5][6][7]

Protoporphyrinogen oxidase is responsible for the seventh step in biosynthesis of protoporphyrin IX. This porphyrin is the precursor to hemoglobin, the oxygen carrier in animals, and chlorophyll, the dye in plants. The enzyme catalyzes the dehydrogenation (removal of hydrogen atoms) of protoporphyrinogen IX (the product of the sixth step in the production of heme) to form protoporphyrin IX. One additional enzyme must modify protoporphyrin IX before it becomes heme. Inhibition of this enzyme is a strategy used in certain herbicides.


The PPOX gene is located on the long (q) arm of chromosome 1 at position 22, from base pair 157,949,266 to base pair 157,954,082.


This gene encodes the penultimate enzyme of heme biosynthesis, which catalyzes the 6-electron oxidation of protoporphyrinogen IX to form protoporphyrin IX. This protein is a flavoprotein associated with the outer surface of the inner mitochondrial membrane.[7]

Heme biosynthetic pathway[edit]

The following genes encode enzymes that catalyze the various steps in the heme biosynthetic pathway:

  • ALAD: aminolevulinate, delta-, dehydratase
  • ALAS1: aminolevulinate, delta-, synthase 1
  • ALAS2: aminolevulinate, delta-, synthase 2 (sideroblastic/hypochromic anemia)
  • CPOX: coproporphyrinogen oxidase
  • FECH: ferrochelatase (protoporphyria)
  • HMBS: hydroxymethylbilane synthase
  • PPOX: protoporphyrinogen oxidase
  • UROD: uroporphyrinogen decarboxylase
  • UROS: uroporphyrinogen III synthase (congenital erythropoietic porphyria)

Clinical significance[edit]

Variegate porphyria is caused by mutations in the PPOX gene. More than 100 mutations that can cause variegate porphyria have been identified in the PPOX gene. One mutation, a substitution of the amino acid tryptophan for arginine at position 59 (also written as Arg59Trp or R59W), is found in about 95 percent of South African families with variegate porphyria. Mutations in the PPOX gene reduce the activity of the enzyme made by the gene, allowing byproducts of heme production to build up in the body. This buildup, in combination with nongenetic factors (such as certain drugs, alcohol and dieting), causes this type of porphyria.

See also[edit]


  1. ^ a b c GRCh38: Ensembl release 89: ENSG00000143224 - Ensembl, May 2017
  2. ^ a b c GRCm38: Ensembl release 89: ENSMUSG00000062729 - Ensembl, May 2017
  3. ^ "Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
  4. ^ "Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
  5. ^ Taketani S, Inazawa J, Abe T, Furukawa T, Kohno H, Tokunaga R, Nishimura K, Inokuchi H (Oct 1995). "The human protoporphyrinogen oxidase gene (PPOX): organization and location to chromosome 1". Genomics. 29 (3): 698–703. doi:10.1006/geno.1995.9949. PMID 8575762.
  6. ^ Frank J, McGrath JA, Poh-Fitzpatrick MB, Hawk JL, Christiano AM (Jul 1999). "Mutations in the translation initiation codon of the protoporphyrinogen oxidase gene underlie variegate porphyria". Clinical and Experimental Dermatology. 24 (4): 296–301. doi:10.1046/j.1365-2230.1999.00484.x. PMID 10457135.
  7. ^ a b "Entrez Gene: PPOX protoporphyrinogen oxidase".

Further reading[edit]

External links[edit]

  • PDBe-KB provides an overview of all the structure information available in the PDB for Human Protoporphyrinogen oxidase