title: Reactions of Ferrous Coproheme Decarboxylase (HemQ) with O2and H2O2Yield Ferric Heme b.
abstract: A recently discovered pathway for the biosynthesis of heme b ends in an unusual reaction catalyzed by coproheme decarboxylase (HemQ), where the Fe(II)-containing coproheme acts as both substrate and cofactor. Because both O2and H2O2are available as cellular oxidants, pathways for the reaction involving either can be proposed. Analysis of reaction kinetics and products showed that, under aerobic conditions, the ferrous coproheme-decarboxylase complex is rapidly and selectively oxidized by O2to the ferric state. The subsequent second-order reaction between the ferric complex and H2O2is slow, pH-dependent, and further decelerated by D2O2(average kinetic isotope effect of 2.2). The observation of rapid reactivity with peracetic acid suggested the possible involvement of Compound I (ferryl porphyrin cation radical), consistent with coproheme and harderoheme reduction potentials in the range of heme proteins that heterolytically cleave H2O2. Resonance Raman spectroscopy nonetheless indicated a remarkably weak Fe-His interaction; how the active site structure may support heterolytic H2O2cleavage is therefore unclear. From a cellular perspective, the use of H2O2as an oxidant in a catalase-positive organism is intriguing, as is the unusual generation of heme b in the Fe(III) rather than Fe(II) state as the end product of heme synthesis.
authors.affiliation: Department of Chemistry and Biochemistry, Montana State University , Bozeman, Montana 59715, United States.
authors.forename: Bennett R
authors.initials: BR
authors.lastname: Streit
authors.affiliation: Department of Chemistry and Biochemistry, Montana State University , Bozeman, Montana 59715, United States.
authors.forename: Arianna I
authors.initials: AI
authors.lastname: Celis
authors.affiliation: Department of Chemistry and Biochemistry, Montana State University , Bozeman, Montana 59715, United States.
authors.forename: Krista
authors.initials: K
authors.lastname: Shisler
authors.affiliation: Department of Chemistry and Biochemistry, North Dakota State University , Fargo, North Dakota 58102, United States.
authors.forename: Kenton R
authors.initials: KR
authors.lastname: Rodgers
authors.affiliation: Department of Chemistry and Biochemistry, North Dakota State University , Fargo, North Dakota 58102, United States.
authors.forename: Gudrun S
authors.initials: GS
authors.lastname: Lukat-Rodgers
authors.affiliation: Department of Chemistry and Biochemistry, Montana State University , Bozeman, Montana 59715, United States.
authors.forename: Jennifer L
authors.identifier: http://orcid.org/0000-0001-5593-3391
authors.initials: JL
authors.lastname: DuBois
mesh_terms: D000332:Aerobiosis; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D053898:Biosynthetic Pathways; D002262:Carboxy-Lyases / Q000737:chemistry / Q000378:metabolism*; D002374:Catalase / Q000378:metabolism; D005290:Ferric Compounds / Q000737:chemistry / Q000378:metabolism; D005296:Ferrous Compounds / Q000737:chemistry / Q000378:metabolism; D006418:Heme / Q000737:chemistry / Q000378:metabolism*; D006427:Hemin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008956:Models, Chemical; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism*; D010463:Peracetic Acid / Q000378:metabolism; D013053:Spectrophotometry; D013059:Spectrum Analysis, Raman; D013211:Staphylococcus aureus / Q000201:enzymology / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D005290:Ferric Compounds; D005296:Ferrous Compounds; C561849:coprohemin; D006418:Heme; D006427:Hemin; D006861:Hydrogen Peroxide; D002374:Catalase; D002262:Carboxy-Lyases; D010463:Peracetic Acid; D010100:Oxygen