title: Peroxidase-type reactions suggest a heterolytic/nucleophilic O-O joining mechanism in the heme-dependent chlorite dismutase.
abstract: Heme-containing chlorite dismutases (Clds) catalyze a highly unusual O-O bond-forming reaction. The O-O cleaving reactions of hydrogen peroxide and peracetic acid (PAA) with the Cld from Dechloromonas aromatica (DaCld) were studied to better understand the Cl-O cleavage of the natural substrate and subsequent O-O bond formation. While reactions with H2O2 result in slow destruction of the heme, at acidic pH heterolytic cleavage of the O-O bond of PAA cleanly yields the ferryl porphyrin cation radical (compound I). At alkaline pH, the reaction proceeds more rapidly, and the first observed intermediate is a ferryl heme. Freeze-quench EPR confirmed that the latter has an uncoupled protein-based radical, indicating that compound I is the first intermediate formed at all pH values and that radical migration is faster at alkaline pH. These results suggest by analogy that two-electron Cl-O bond cleavage to yield a ferryl-porphyrin cation radical is the most likely initial step in O-O bond formation from chlorite.
authors.affiliation: Department of Chemistry and Biochemistry, University of Notre Dame , Notre Dame, Indiana 46556, United States.
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Mayfield
authors.forename: Béatrice
authors.initials: B
authors.lastname: Blanc
authors.forename: Kenton R
authors.initials: KR
authors.lastname: Rodgers
authors.forename: Gudrun S
authors.initials: GS
authors.lastname: Lukat-Rodgers
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: DuBois
mesh_terms: D006418:Heme / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008956:Models, Chemical; D010088:Oxidoreductases / Q000737:chemistry / Q000378:metabolism*; D010463:Peracetic Acid / Q000737:chemistry / Q000378:metabolism; D009195:Peroxidase / Q000378:metabolism; D010545:Peroxides / Q000737:chemistry*; D043362:Rhodocyclaceae / Q000201:enzymology
chemical_list: D010545:Peroxides; D006418:Heme; D006861:Hydrogen Peroxide; D010088:Oxidoreductases; D009195:Peroxidase; C402794:chlorite dismutase; D010463:Peracetic Acid