title: Evidence for heme oxygenase activity in a heme peroxidase.
abstract: The heme peroxidase and heme oxygenase enzymes share a common heme prosthetic group but catalyze fundamentally different reactions, the first being H(2)O(2)-dependent oxidation of substrate using an oxidized Compound I intermediate, and the second O(2)-dependent degradation of heme. It has been proposed that these enzymes utilize a common reaction intermediate, a ferric hydroperoxide species, that sits at a crossroads in the mechanism and beyond which there are two mutually exclusive mechanistic pathways. Here, we present evidence to support this proposal in a heme peroxidase. Hence, we describe kinetic data for a variant of ascorbate peroxidase (W41A) which reacts slowly with tert-butyl hydroperoxide and does not form the usual peroxidase Compound I intermediate; instead, structural data show that a product is formed in which the heme has been cleaved at the alpha-meso position, analogous to the heme oxygenase mechanism. We interpret this to mean that the Compound I (peroxidase) pathway is shut down, so that instead the reaction intermediate diverts through the alternative (heme oxygenase) route. A mechanism for formation of the product is proposed and discussed in the light of what is known about the heme oxygenase reaction mechanism.
authors.affiliation: Department of Chemistry, Henry Wellcome Building, University of Leicester, University Road, Leicester LE1 7RH, UK.
authors.forename: Sandip K
authors.initials: SK
authors.lastname: Badyal
authors.forename: Graham
authors.initials: G
authors.lastname: Eaton
authors.forename: Sharad
authors.initials: S
authors.lastname: Mistry
authors.forename: Zoi
authors.initials: Z
authors.lastname: Pipirou
authors.forename: Jaswir
authors.initials: J
authors.lastname: Basran
authors.forename: Clive L
authors.initials: CL
authors.lastname: Metcalfe
authors.forename: Andrea
authors.initials: A
authors.lastname: Gumiero
authors.forename: Sandeep
authors.initials: S
authors.lastname: Handa
authors.forename: Peter C E
authors.initials: PC
authors.lastname: Moody
authors.forename: Emma Lloyd
authors.initials: EL
authors.lastname: Raven
mesh_terms: D060387:Ascorbate Peroxidases; D001224:Aspartic Acid / Q000235:genetics; D003460:Crystallization; D018360:Crystallography, X-Ray; D014644:Genetic Variation; D006419:Heme Oxygenase (Decyclizing) / Q000737:chemistry* / Q000378:metabolism*; D007527:Isoenzymes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010544:Peroxidases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013025:Glycine max / Q000201:enzymology / Q000235:genetics; D014364:Tryptophan / Q000235:genetics; D020122:tert-Butylhydroperoxide / Q000737:chemistry / Q000378:metabolism
chemical_list: D007527:Isoenzymes; D010940:Plant Proteins; D001224:Aspartic Acid; D014364:Tryptophan; D020122:tert-Butylhydroperoxide; D010544:Peroxidases; D060387:Ascorbate Peroxidases; D006419:Heme Oxygenase (Decyclizing)