title: Pathways of Transmembrane Electron Transfer in Cytochrome bc Complexes: Dielectric Heterogeneity and Interheme Coulombic Interactions.
abstract: The intramembrane cytochrome bc1complex of the photosynthetic bacterium Rhodobacter capsulatus and the cytochrome b6f complex, which functions in oxygenic photosynthesis, utilize two pairs of b-hemes in a symmetric dimer to accomplish proton-coupled electron transfer. The transmembrane electron transfer pathway in each complex was identified through the novel use of heme Soret band excitonic circular dichroism (CD) spectra, for which the responsible heme-heme interactions were determined from crystal structures. Kinetics of heme reduction and CD amplitude change were measured simultaneously. For bc1, in which the redox potentials of the transmembrane heme pair are separated by 160 mV, heme reduction occurs preferentially to the higher-potential intermonomer heme pair on the electronegative (n) side of the complex. This contrasts with the b6f complex, where the redox potential difference between transmembrane intramonomer p- and n-side hemes is substantially smaller and the n-p pair is preferentially reduced. Limits on the dielectric constant between intramonomer hemes were calculated from the interheme distance and the redox potential difference, ΔEm. The difference in preferred reduction pathway is a consequence of the larger ΔEmbetween n- and p-side hemes in bc1, which favors the reduction of n-side hemes and cannot be offset by decreased repulsive Coulombic interactions between intramonomer hemes.
authors.forename: S
authors.identifier: 0000-0001-8432-2194
authors.initials: S
authors.lastname: Bhaduri
authors.forename: V
authors.initials: V
authors.lastname: Stadnytskyi
authors.forename: S D
authors.initials: SD
authors.lastname: Zakharov
authors.forename: S Saif
authors.initials: SS
authors.lastname: Hasan
authors.affiliation: Department of Molecular Biophysics, Faculty of Biochemistry, Biophysics, and Biotechnology, Jagiellonian University , Kraków 31-007, Poland.
authors.forename: Ł
authors.initials: Ł
authors.lastname: Bujnowicz
authors.affiliation: Department of Molecular Biophysics, Faculty of Biochemistry, Biophysics, and Biotechnology, Jagiellonian University , Kraków 31-007, Poland.
authors.forename: M
authors.initials: M
authors.lastname: Sarewicz
authors.forename: S
authors.initials: S
authors.lastname: Savikhin
authors.affiliation: Department of Molecular Biophysics, Faculty of Biochemistry, Biophysics, and Biotechnology, Jagiellonian University , Kraków 31-007, Poland.
authors.forename: A
authors.initials: A
authors.lastname: Osyczka
authors.forename: W A
authors.initials: WA
authors.lastname: Cramer
mesh_terms: D000818:Animals; D002942:Circular Dichroism; D056831:Coordination Complexes / Q000737:chemistry*; D018360:Crystallography, X-Ray; D003580:Cytochromes / Q000737:chemistry / Q000378:metabolism*; D004579:Electron Transport; D014450:Electron Transport Complex III / Q000737:chemistry; D006418:Heme / Q000737:chemistry; D006801:Humans; D007700:Kinetics; D008566:Membranes / Q000378:metabolism; D008958:Models, Molecular; D010084:Oxidation-Reduction; D015398:Signal Transduction
chemical_list: D056831:Coordination Complexes; D003580:Cytochromes; D006418:Heme; D014450:Electron Transport Complex III