Hemoprotein models based on a covalent helix-heme-helix sandwich. 3. Coordination properties, reactivity and catalytic application of Fe(III)- and Fe(II)-mimochrome I |
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Authors: | Flavia Nastri Angela Lombardi G Morelli Carlo Pedone Vincenzo Pavone Geneviève Chottard Pierrette Battioni Daniel Mansuy |
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Institution: | (1) Centro Interdipartimentale sui Peptidi Bioattivi & Centro di Studio di Biocristallografia – CNR, Via Mezzocannone 4, I-80134 Naples, Italy Fax: +39-81-5527771; e-mail: MORELLI@chemna.dichi.unina.it, IT;(2) Université Paris VI, Chimie des Métaux de Transition, Case 42, 4 place Jussieu, F-75252 Paris Cedex 05, France, FR;(3) URA 400 CNRS, Université Paris V, Laboratoire de Chimie et de Biochimie, 45 rue des Saints-Pères, F-75270 Paris Cedex 06, France, FR |
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Abstract: | The coordination state of Fe(III)- and Fe(II)-mimochrome I, a covalent peptide-deuteroheme sandwich involving two nonapeptides
bearing a histidine residue in a central position, was studied by UV-visible, EPR, and resonance Raman spectroscopy. The ferric
and ferrous states of this new iron species mainly exist, at pH 7, in a low-spin hexacoordinate form with two axial histidine
ligands coming from the peptide chains. A minor amount of high-spin form for the ferric state is also present at pH 7. However,
it is mainly high-spin at pH 2 or in DMSO. Fe(II)-mimochrome I binds CO with an affinity comparable to that of myoglobin and
hemoglobin. Fe(III)-mimochrome I reacts with alkylhydroxylamine and arylhydrazines, leading to the corresponding Fe(II)-nitrosoalkyl
and Fe(III)-σ-aryl complexes, respectively. These reactions were greatly dependent on the solvent used and on the pH, and
were much slower than the corresponding reactions performed by deuterohemin in the presence of excess imidazole. All these
results indicate that the reactivity of iron-mimochrome I is controlled by the binding of the peptide chains to the iron.
The reactivity shown by this complex at neutral pH is intermediate between that observed for iron porphyrins in the presence
of excess imidazole and that of hemoproteins characterized by a strong bis-histidine axial coordination, such as cytochrome
b
5. Fe(III)-mimochrome I is able to catalyze styrene epoxidation by using a Fe(III)-mimochrome I]/H2O2]/stryrene] ratio of 1 : 10 : 2000 in phosphate buffer solution (pH 7.2) containing 2% CTAB both under strictly anaerobic
conditions and in the presence of oxygen, at 0 °C.
Received: 26 May 1998 / Accepted: 20 August 1998 |
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Keywords: | Hemoprotein models Iron-porphyrin peptides Epr Resonance raman Styrene catalytic epoxidation |
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