|Gene:||hemG||Accession Numbers: EG11485 (MetaCyc), b3850, ECK3842|
Species: Escherichia coli K-12 substr. MG1655
Subunit composition of protoporphyrinogen oxidase = [HemG]4
Protoporphyrinogen oxidase (PPO) catalyzes the six-electron oxidation of protoporphyrinogen IX to protoporphyrin IX. The enzyme belongs to the flavodoxin family of proteins, and the long chain insert loop which distinguishes it from other flavodoxins may be responsible for PPO activity [Boynton09].
Under aerobic conditions, the electron acceptor for the protoporphyrinogen oxidase reaction was thought to be molecular oxygen [Jacobs76]. Under anaerobic conditions, the reaction can be coupled to nitrate or fumarate reduction within the anaerobic electron transport chain [Jacobs76, Jacobs77]. Protoporphyrinogen oxidase is inactivated by treatment with detergent, suggesting that the enzyme requires an intact electron transport system for activity [Jacobs84]. In vitro, the purified enzyme can use menadione as the electron acceptor [Boynton09].
The presence of a flavodoxin motif in the sequence indicates that the enzyme may utilize FMN as a cofactor [Nishimura95]. A probable FMN cofactor was detected by MALDI-TOF, measurement of the UV-visible spectrum, and the EPR signal during redox titrations [Boynton09].
In later work, potential electron transport chains for both aerobic and anaerobic E. coli HemG protoporphyrinogen oxidase activity were reconstituted in vitro from purified components and tested. Ubiquinone and menaquinone functioned as electron acceptors during HemG catalysis. Fumarate reductase, nitrate reductase, cytochrome bd and cytochrome bo were shown to function as electron acceptors for HemG. In vivo experiments using E. coli respiratory chain mutant strains confirmed the in vitro results. These data showed that HemG catalysis and overall heme biosynthesis is dependent upon respiratory electron transport. A model for respiratory chain-driven protoporphyrinogen oxidase was proposed [Mobius10].
There is a disagreement in the literature regarding the oligomerization state of purified, recombinant HemG. In [Mobius10] a homohexamer was determined by high performance gel permeation chromatography, whereas in [Boynton09] a homotetramer was determined by gel filtration FPLC .
Locations: cytosol, membrane
|Map Position: [4,032,631 -> 4,033,176]|
Molecular Weight of Polypeptide: 21.226 kD (from nucleotide sequence)
Unification Links: ASAP:ABE-0012577 , CGSC:642 , DIP:DIP-35890N , EchoBASE:EB1448 , EcoGene:EG11485 , EcoliWiki:b3850 , ModBase:P0ACB4 , OU-Microarray:b3850 , PortEco:hemG , Protein Model Portal:P0ACB4 , RefSeq:NP_418292 , RegulonDB:EG11485 , String:511145.b3850 , UniProt:P0ACB4
Relationship Links: InterPro:IN-FAMILY:IPR001226 , InterPro:IN-FAMILY:IPR008254 , InterPro:IN-FAMILY:IPR026816 , InterPro:IN-FAMILY:IPR029039 , Pfam:IN-FAMILY:PF12724 , Prosite:IN-FAMILY:PS00201 , Prosite:IN-FAMILY:PS50902
|Biological Process:||GO:0006779 - porphyrin-containing compound biosynthetic process
GO:0006783 - heme biosynthetic process [Sasarman79]
GO:0006782 - protoporphyrinogen IX biosynthetic process [UniProtGOA12]
GO:0055114 - oxidation-reduction process [UniProtGOA11]
|Molecular Function:||GO:0004729 - oxygen-dependent protoporphyrinogen oxidase activity
GO:0010181 - FMN binding [GOA01, Boynton09]
GO:0042802 - identical protein binding [Mobius10, Boynton09]
GO:0070819 - menaquinone-dependent protoporphyrinogen oxidase activity [Boynton09]
GO:0009055 - electron carrier activity [GOA01]
GO:0016491 - oxidoreductase activity [UniProtGOA11, GOA01]
|Cellular Component:||GO:0005829 - cytosol
GO:0016020 - membrane [Jacobs78]
|MultiFun Terms:||metabolism → biosynthesis of building blocks → cofactors, small molecule carriers → heme, porphyrine|
Enzymatic reaction of: protoporphyrinogen oxidase
Synonyms: protoporphyrinogen-IX:oxygen oxidoreductase, PPO
EC Number: 220.127.116.11
The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the direction in which it was curated.
The reaction is physiologically favored in the direction shown.
Enzymatic reaction of: protoporphyrinogen dehydrogenase (protoporphyrinogen oxidase)
EC Number: 18.104.22.168
With fumarate as the final electron acceptor, the reaction is dependent on menaquinone as the electron carrier and is independent of cytochromes [Jacobs78].
The enzymatic activity is specific for protoporphyrinogen IX [Boynton09].
|Conserved-Region||3 -> 172|
1/26/1998 (pkarp) Merged genes G7810/b3850 and EG11485/hemG
Boynton09: Boynton TO, Daugherty LE, Dailey TA, Dailey HA (2009). "Identification of Escherichia coli HemG as a novel, menadione-dependent flavodoxin with protoporphyrinogen oxidase activity." Biochemistry 48(29):6705-11. PMID: 19583219
Breckau03: Breckau D, Mahlitz E, Sauerwald A, Layer G, Jahn D (2003). "Oxygen-dependent coproporphyrinogen III oxidase (HemF) from Escherichia coli is stimulated by manganese." J Biol Chem 278(47);46625-31. PMID: 12975365
DiazMejia09: Diaz-Mejia JJ, Babu M, Emili A (2009). "Computational and experimental approaches to chart the Escherichia coli cell-envelope-associated proteome and interactome." FEMS Microbiol Rev 33(1);66-97. PMID: 19054114
Jacobs77: Jacobs NJ, Jacobs JM (1977). "Evidence for involvement of the electron transport system at a late step of anaerobic microbial heme synthesis." Biochim Biophys Acta 459(1);141-4. PMID: 318855
Jacobs84: Jacobs JM, Jacobs NJ (1984). "Protoporphyrinogen oxidation, an enzymatic step in heme and chlorophyll synthesis: partial characterization of the reaction in plant organelles and comparison with mammalian and bacterial systems." Arch Biochem Biophys 229(1);312-9. PMID: 6703698
Mobius10: Mobius K, Arias-Cartin R, Breckau D, Hannig AL, Riedmann K, Biedendieck R, Schroder S, Becher D, Magalon A, Moser J, Jahn M, Jahn D (2010). "Heme biosynthesis is coupled to electron transport chains for energy generation." Proc Natl Acad Sci U S A 107(23);10436-41. PMID: 20484676
Narita99: Narita S, Taketani S, Inokuchi H (1999). "Oxidation of protoporphyrinogen IX in Escherichia coli is mediated by the aerobic coproporphyrinogen oxidase." Mol Gen Genet 1999;261(6);1012-20. PMID: 10485293
Nishimura95: Nishimura K, Nakayashiki T, Inokuchi H (1995). "Cloning and identification of the hemG gene encoding protoporphyrinogen oxidase (PPO) of Escherichia coli K-12." DNA Res 1995;2(1);1-8. PMID: 7788523
Sasarman93: Sasarman A, Letowski J, Czaika G, Ramirez V, Nead MA, Jacobs JM, Morais R (1993). "Nucleotide sequence of the hemG gene involved in the protoporphyrinogen oxidase activity of Escherichia coli K12." Can J Microbiol 39(12);1155-61. PMID: 7916647
Zhang07: Zhang N, Chen R, Young N, Wishart D, Winter P, Weiner JH, Li L (2007). "Comparison of SDS- and methanol-assisted protein solubilization and digestion methods for Escherichia coli membrane proteome analysis by 2-D LC-MS/MS." Proteomics 7(4);484-93. PMID: 17309111
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