title: Ferric microperoxidase-11 catalyzes peroxynitrite isomerization.
abstract: Microperoxidase-11 (MP11) is an undecapeptide derived from horse heart cytochrome c offering the possibility to study the reactivity of the heme group relatively unshielded by the protein. Here, the peroxynitrite isomerization to NO3(-) catalyzed by ferric MP11 (MP11-Fe(III)) is reported. Data were obtained between pH3.6 and 8.1, at 20.0°C. The value of the second-order rate constant (kon) for peroxynitrite isomerization to NO3(-) by MP11-Fe(III) decreases from (1.1±0.1)×10(5)M(-1)s(-1), at pH3.6, to (6.1±0.6)×10(3)M(-1)s(-1), at pH8.1. The pH dependence of kon (pKa=6.9) suggests that peroxynitrous acid reacts preferentially with MP11-Fe(III). The MP11-Fe(III)-catalyzed isomerization of peroxynitrite to NO3(-) has been ascribed to the reactive penta-coordinated heme-Fe atom of MP11-Fe(III). In fact, cyanide binding to the sixth coordination position of the heme-Fe atom inhibits the MP11-Fe(III)-catalyzed isomerization of peroxynitrite to NO3(-). The values of the first-order rate constant (k0) for isomerization of peroxynitrite to NO3(-) in the presence of the MP11-Fe(III)-CN complex are superimposable to those obtained in the absence of MP-Fe(III). Values of kon for peroxynitrite isomerization to NO3(-) by MP11-Fe(III) overlap those obtained for penta-coordinated cardiolipin-cytochrome c complex and for carboxymethylated cytochrome c in absence and presence of cardiolipin. Present results highlight the role of the heme-Fe(III) co-ordination state in the modulation of cytochrome c reactivity.
authors.affiliation: Interdepartmental Laboratory for Electron Microscopy, Roma Tre University, I-00146 Roma, Italy; Institute of Protein Biochemistry National Research Council, I-80131, Napoli, Italy. Electronic address: ascenzi@uniroma3.it.
authors.forename: Paolo
authors.initials: P
authors.lastname: Ascenzi
authors.affiliation: Interdepartmental Laboratory for Electron Microscopy, Roma Tre University, I-00146 Roma, Italy.
authors.forename: Loris
authors.initials: L
authors.lastname: Leboffe
authors.affiliation: Department of Clinical Sciences and Translational Medicine, University of Roma "Tor Vergata", I-00133 Roma, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Santucci
authors.affiliation: Department of Clinical Sciences and Translational Medicine, University of Roma "Tor Vergata", I-00133 Roma, Italy; Interuniversity Consortium for the Research on the Chemistry of Metals in Biological Systems, I-70126 Bari, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Coletta
mesh_terms: D055162:Biocatalysis; D002308:Cardiolipins / Q000737:chemistry; D003486:Cyanides / Q000737:chemistry; D045304:Cytochromes c / Q000737:chemistry / Q000378:metabolism; D005290:Ferric Compounds / Q000737:chemistry / Q000378:metabolism*; D006418:Heme / Q000378:metabolism; D007536:Isomerism; D007700:Kinetics; D010544:Peroxidases / Q000737:chemistry / Q000378:metabolism*; D030421:Peroxynitrous Acid / Q000737:chemistry*
chemical_list: D002308:Cardiolipins; D003486:Cyanides; D005290:Ferric Compounds; D030421:Peroxynitrous Acid; D006418:Heme; D045304:Cytochromes c; D010544:Peroxidases; C021799:microperoxidase
keywords: Ferric microperoxidase; Kinetics; Peroxynitrite isomerization