Cytochrome C

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Cytochrome c Cytoplasmic chromophore100 amino acids, 12 kDa. Heme Fe coordinated by His and Met. Single electron transfer. Covalently attached to the protein at Cys side chains, via heme propionates. E°’ = 250 mV http://en.wikipedia.org/wiki/Cytochrome_c A.-F. Miller, 2008, pg 1 Heme Fe A.-F. Miller, 2008, pg 2 Garrett & Grisham, Figure 5.31 O2 vibrational frequencies (how to know its effective oxidation state) -1 Species νO-O(cm ) dO-O(Å) + O2 1,905 1.12 O2+ 1,580 1.21 - O2 1,097 1.33 2- O2 802 1.49 A.-F. Miller, 2008, pg 3 II O2 binding to Fe is associated with electron transfer From resonance Raman spectroscopy, the O-O stretch in -1 5 III - oxyMb is ≈ 1,105 cm , protein is diamagnetic, d , Fe -O2 A.-F. Miller, 2008, pg 4 A.-F. Miller, 2008, pg 5 Garrett & Grisham, Fig. 20.10, 20.09 Myoglobin A.-F. Miller, 2008, pg 6 Cytochrome P450 Cytoplasmic chromophore absorbing at 450 nm Also: Chloroperoxidase and NO synthase, peroxidase. - + RH + O2 + 2 e + 2 H → ROH + H2O Heme Fe has one protein ligand, from Cys S-. E°’m = -220, changes to -140 upon substrate binding. Metabolism of xenobiotics, activation of drugs, hormones and prostaglandins. Chloroperoxidases (such as myeloperoxidase) use H2O2 as the O source: immune function. A.-F. Miller, 2008, pg 7 Substrate binding to the protein is associated with Mechanism release of water from second Fe3+ coordination site and H H conversion of the heme from O low-spin to high-spin. Fe3+ can then be reduced more easily to Fe2+ and bind O2. O Peroxo intermediate converts to FeIV=O 2 intermediate. ⇔ III - A.-F. Miller, 2008, pg 8 Fe -OO ‘Peroxide shunt’ Mechanism The fact that addition of H H O peroxide achieves the same intermediate as is formed upon O2 addition to reduced enzyme shows that the O enzyme gives those two reducing 2 equivalents to O2. ⇔ III - A.-F. Miller, 2008, pg 9 Fe -OO ‘Compound one’ and ‘compound two’ Cpd I formed from H2O2 + P450 When a remote amino acid is the source of the other electron (and becomes a radical: Cytochrome c peroxidase uses a Trp•), then the spectral properties are those of CpdII. Cpd II is reduced by one electron relative to Cpd I A.-F. Miller, 2008, pg 10 Spin state change and oxidation state change are coupled to substrate binding Das et al. (2007) J.A.C.S. 129:13378-13379 A.-F. Miller, 2008, pg 11 Das et al. (2007) JACS 129:13378-13379 A.-F. Miller, 2008, pg 12.

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A Copper Protein and a Cytochrome Bind at the Same Site on Bacterial Cytochrome C Peroxidase† Sofia R
14566 Biochemistry 2004, 43, 14566-14576 A Copper Protein and a Cytochrome Bind at the Same Site on Bacterial Cytochrome c Peroxidase† Sofia R. Pauleta,‡,§ Alan Cooper,⊥ Margaret Nutley,⊥ Neil Errington,| Stephen Harding,| Francoise Guerlesquin,3 Celia F. Goodhew,‡ Isabel Moura,§ Jose J. G. Moura,§ and Graham W. Pettigrew‡ Veterinary Biomedical Sciences, Royal (Dick) School of Veterinary Studies, UniVersity of Edinburgh, Summerhall, Edinburgh EH9 1QH, U.K., Department of Chemistry, UniVersity of Glasgow, Glasgow G12 8QQ, U.K., Centre for Macromolecular Hydrodynamics, UniVersity of Nottingham, Sutton Bonington, Nottingham LE12 5 RD, U.K., Unite de Bioenergetique et Ingenierie des Proteines, IBSM-CNRS, 31 chemin Joseph Aiguier, 13402 Marseilles cedex 20, France, Requimte, Departamento de Quimica, CQFB, UniVersidade NoVa de Lisboa, 2829-516 Monte de Caparica, Portugal ReceiVed July 5, 2004; ReVised Manuscript ReceiVed September 9, 2004 ABSTRACT: Pseudoazurin binds at a single site on cytochrome c peroxidase from Paracoccus pantotrophus with a Kd of 16.4 µMat25°C, pH 6.0, in an endothermic reaction that is driven by a large entropy change. Sedimentation velocity experiments confirmed the presence of a single site, although results at higher pseudoazurin concentrations are complicated by the dimerization of the protein. Microcalorimetry, ultracentrifugation, and 1H NMR spectroscopy studies in which cytochrome c550, pseudoazurin, and cytochrome c peroxidase were all present could be modeled using a competitive binding algorithm. Molecular docking simulation of the binding of pseudoazurin to the peroxidase in combination with the chemical shift perturbation pattern for pseudoazurin in the presence of the peroxidase revealed a group of solutions that were situated close to the electron-transferring heme with Cu-Fe distances of about 14 Å.
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