PPOX

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.

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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

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.

References

• Elder GH (1998). "Genetic defects in the porphyrias: types and significance". Clin Dermatol 16 (2): 225-33. PMID 9554235.
• Maneli MH, Corrigall AV, Klump HH, Davids LM, Kirsch RE, Meissner PN (2003). "Kinetic and physical characterisation of recombinant wild-type and mutant human protoporphyrinogen oxidases". Biochim Biophys Acta 1650 (1-2): 10-21. PMID 12922165.
• Morgan RR, Errington R, Elder GH (2004). "Identification of sequences required for the import of human protoporphyrinogen oxidase to mitochondria". Biochem J 377 (Pt 2): 281-7. PMID 14535846.
• Sassa S, Kappas A (2000). "Molecular aspects of the inherited porphyrias". J Intern Med 247 (2): 169-78. PMID 10692079.

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