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Protoporphyrinogen oxidase
Available structures
PDB Ortholog search: PDBe, RCSB
Symbols PPOX ; PPO; V290M; VP
External IDs OMIM600923 MGI104968 HomoloGene262 GeneCards: PPOX Gene
EC number
RNA expression pattern
PBB GE PPOX 204788 s at tn.png
More reference expression data
Species Human Mouse
Entrez 5498 19044
Ensembl ENSG00000143224 ENSMUSG00000062729
UniProt P50336 P51175
RefSeq (mRNA) NM_000309 NM_008911
RefSeq (protein) NP_000300 NP_032937
Location (UCSC) Chr 1:
161.14 – 161.15 Mb
Chr 1:
171.28 – 171.28 Mb
PubMed search [1] [2]

Protoporphyrinogen oxidase is an enzyme that in humans is encoded by the PPOX gene.[1][2][3]

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. Mutations in this gene cause variegate porphyria.[3]

PPOX (protoporphyrinogen oxidase) is a human gene that produces an enzyme called protoporphyrinogen oxidase. This enzyme is responsible for the seventh step in heme production. Heme is the portion of hemoglobin that carries oxygen in the blood from the lungs to the rest of the body. Each of the steps in heme production is controlled by a separate gene (see below). Protoporphyrinogen oxidase removes hydrogen atoms from 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.

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.

The following genes are part of the chemical pathway for making heme.

  • 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)

Related conditions[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.


This article incorporates public domain text from The U.S. National Library of Medicine


  1. ^ Taketani S, Inazawa J, Abe T, Furukawa T, Kohno H, Tokunaga R, Nishimura K, Inokuchi H (Mar 1996). "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. 
  2. ^ Frank J, McGrath JA, Poh-Fitzpatrick MB, Hawk JL, Christiano AM (Sep 1999). "Mutations in the translation initiation codon of the protoporphyrinogen oxidase gene underlie variegate porphyria". Clin Exp Dermatol 24 (4): 296–301. doi:10.1046/j.1365-2230.1999.00484.x. PMID 10457135. 
  3. ^ a b "Entrez Gene: PPOX protoporphyrinogen oxidase". 

Further reading[edit]

External links[edit]