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Normal Function
The PPOX gene provides instructions for making an enzyme known as protoporphyrinogen oxidase. This enzyme is involved in the production of a molecule called heme. Heme is vital for all of the body's organs, although it is most abundant in the blood, bone marrow, and liver. Heme is an essential component of iron-containing proteins called hemoproteins, including hemoglobin (the protein that carries oxygen in the blood).
The production of heme is a multi-step process that requires eight different enzymes. Protoporphyrinogen oxidase is responsible for the seventh step in this process, in which two hydrogen atoms are removed from protoporphyrinogen IX (the product of the sixth step) to form protoporphyrin IX. In the final step, another enzyme modifies protoporphyrin IX by inserting an iron atom to produce heme.
Health Conditions Related to Genetic Changes
Porphyria
More than 130 mutations in the PPOX gene have been identified in people with a form of porphyria called variegate porphyria. A particular PPOX gene mutation is found in about 95 percent of South African families with this form of the disorder. The mutation changes a single protein building block (amino acid) in protoporphyrinogen oxidase, replacing the amino acid arginine with the amino acid tryptophan at position 59 (written as Arg59Trp or R59W).
Mutations in the PPOX gene reduce the activity of protoporphyrinogen oxidase, allowing compounds called porphyrin precursors to build up in the body. These compounds are formed during the normal process of heme production, but reduced activity of protoporphyrinogen oxidase allows them to accumulate to toxic levels. Nongenetic factors such as certain drugs, alcohol, dieting, as well as other genetic factors that have not been identified, also contribute to the characteristic features of variegate porphyria.
More About This Health ConditionOther Names for This Gene
- PPO
- PPOX_HUMAN
- protoporphyrinogen dehydrogenase
- protoporphyrinogen IX oxidase
- protoporphyrinogenase
- protox
Additional Information & Resources
Tests Listed in the Genetic Testing Registry
Scientific Articles on PubMed
Catalog of Genes and Diseases from OMIM
References
- Badminton MN, Elder GH. Molecular mechanisms of dominant expression in porphyria. J Inherit Metab Dis. 2005;28(3):277-86. doi: 10.1007/s10545-005-8050-3. Citation on PubMed
- de Villiers JN, Kotze MJ, van Heerden CJ, Sadie A, Gardner HF, Liebenberg J, van Zyl R, du Plessis L, Kimberg M, Frank J, Warnich L. Overrepresentation of the founder PPOX gene mutation R59W in a South African patient with severe clinical manifestation of porphyria. Exp Dermatol. 2005 Jan;14(1):50-5. doi: 10.1111/j.0906-6705.2005.00228.x. Citation on PubMed
- Elder GH. Genetic defects in the porphyrias: types and significance. Clin Dermatol. 1998 Mar-Apr;16(2):225-33. doi: 10.1016/s0738-081x(97)00202-2. No abstract available. Citation on PubMed
- Kauppinen R. Porphyrias. Lancet. 2005 Jan 15-21;365(9455):241-52. doi: 10.1016/S0140-6736(05)17744-7. Citation on PubMed
- Maneli MH, Corrigall AV, Klump HH, Davids LM, Kirsch RE, Meissner PN. Kinetic and physical characterisation of recombinant wild-type and mutant human protoporphyrinogen oxidases. Biochim Biophys Acta. 2003 Aug 21;1650(1-2):10-21. doi: 10.1016/s1570-9639(03)00186-9. Citation on PubMed
- Morgan RR, Errington R, Elder GH. Identification of sequences required for the import of human protoporphyrinogen oxidase to mitochondria. Biochem J. 2004 Jan 15;377(Pt 2):281-7. doi: 10.1042/BJ20030978. Citation on PubMed or Free article on PubMed Central
- Sassa S, Kappas A. Molecular aspects of the inherited porphyrias. J Intern Med. 2000 Feb;247(2):169-78. doi: 10.1046/j.1365-2796.2000.00618.x. Citation on PubMed
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