title: Cyanide binding to ferrous and ferric microperoxidase-11.
abstract: Microperoxidase-11 (MP11) is an undecapeptide derived from horse heart cytochrome c (cytc). MP11 is characterized by a covalently linked solvent-exposed heme group, the heme-Fe atom being axially coordinated by a histidyl residue. Here, the reactions of ferrous and ferric MP11 (MP11-Fe(II) and MP11-Fe(III), respectively) with cyanide have been investigated from the kinetic and thermodynamic viewpoints, at pH 7.0 and 20.0 °C. Values of the second-order rate constant for cyanide binding to MP11-Fe(II) and MP11-Fe(III) are 4.5 M(-1) s(-1) and 8.9 × 10(3) M(-1) s(-1), respectively. Values of the first-order rate constant for cyanide dissociation from ligated MP11-Fe(II) and MP11-Fe(III) are 1.8 × 10(-1) s(-1) and 1.5 × 10(-3) s(-1), respectively. Values of the dissociation equilibrium constant for cyanide binding to MP11-Fe(II) and MP11-Fe(III) are 3.7 × 10(-2) and 1.7 × 10(-7) M, respectively, matching very well with those calculated from kinetic parameters so that no intermediate species seem to be involved in the ligand-binding process. The pH-dependence of cyanide binding to MP11-Fe(III) indicates that CN(-) is the only binding species. Present results have been analyzed in parallel with those of several heme-proteins, suggesting that (1) the ligand accessibility to the metal center and cyanide ionization may modulate the formation of heme-Fe-cyanide complexes, and (2) the general polarity of the heme pocket and/or hydrogen bonding of the heme-bound ligand may affect cyanide exit from the protein matrix. Microperoxidase-11 (MP11) is an undecapeptide derived from horse heart cytochrome c. Penta-coordinated MP11 displays a very high reactivity towards cyanide, whereas the reactivity of hexa-coordinated horse heart cytochrome c is very low.
authors.affiliation: Interdepartmental Laboratory for Electron Microscopy, Roma Tre University, Via della Vasca Navale 79, 00146, Rome, Italy. ascenzi@uniroma3.it.|Institute of Protein Biochemistry, CNR, Via Pietro Castellino 111, 80181, Naples, Italy. ascenzi@uniroma3.it.
authors.forename: Paolo
authors.initials: P
authors.lastname: Ascenzi
authors.affiliation: Department of Clinical Sciences and Translational Medicine, University of Roma "Tor Vergata", Via Montpellier 1, 00133, Rome, Italy.|Interuniversity Consortium for the Research on Chemistry of Metals in Biological Systems, Via Celso Ulpiani 1, 70125, Bari, Italy.
authors.forename: Diego
authors.initials: D
authors.lastname: Sbardella
authors.affiliation: Department of Clinical Sciences and Translational Medicine, University of Roma "Tor Vergata", Via Montpellier 1, 00133, Rome, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Santucci
authors.affiliation: Department of Clinical Sciences and Translational Medicine, University of Roma "Tor Vergata", Via Montpellier 1, 00133, Rome, Italy.|Interuniversity Consortium for the Research on Chemistry of Metals in Biological Systems, Via Celso Ulpiani 1, 70125, Bari, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Coletta
mesh_terms: D000818:Animals; D001665:Binding Sites; D003486:Cyanides / Q000737:chemistry / Q000378:metabolism*; D005290:Ferric Compounds / Q000737:chemistry / Q000378:metabolism*; D005296:Ferrous Compounds / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D010544:Peroxidases / Q000737:chemistry / Q000378:metabolism*; D050661:Sperm Whale; D013816:Thermodynamics
chemical_list: D003486:Cyanides; D005290:Ferric Compounds; D005296:Ferrous Compounds; D010544:Peroxidases; C021799:microperoxidase
keywords: Cyanide binding; Cytochrome c; Kinetics; Microperoxidase-11; Thermodynamics