title: Evidence for Fast Electron Transfer between the High-Spin Haems in Cytochrome bd-I from Escherichia coli.
abstract: Cytochrome bd-I is one of the three proton motive force-generating quinol oxidases in the O2-dependent respiratory chain of Escherichia coli. It contains one low-spin haem (b558) and the two high-spin haems (b595 and d) as the redox-active cofactors. In order to examine the flash-induced intraprotein reverse electron transfer (the so-called ''electron backflow''), CO was photolyzed from the ferrous haem d in one-electron reduced (b5583+b5953+d2+-CO) cytochrome bd-I, and the fully reduced (b5582+b5952+d2+-CO) oxidase as a control. In contrast to the fully reduced cytochrome bd-I, the transient spectrum of one-electron reduced oxidase at a delay time of 1.5 μs is clearly different from that at a delay time of 200 ns. The difference between the two spectra can be modeled as the electron transfer from haem d to haem b595 in 3-4% of the cytochrome bd-I population. Thus, the interhaem electron backflow reaction induced by photodissociation of CO from haem d in one-electron reduced cytochrome bd-I comprises two kinetically different phases: the previously unnoticed fast electron transfer from haem d to haem b595 within 0.2-1.5 μs and the slower well-defined electron equilibration with τ ~16 μs. The major new finding of this work is the lack of electron transfer at 200 ns.
authors.affiliation: Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russian Federation.
authors.forename: Sergey A
authors.initials: SA
authors.lastname: Siletsky
authors.affiliation: Institut de Biologie Physico-Chimique, Unite Mixte de Recherche 7141 CNRS, Universite Paris 6, Paris, France.
authors.forename: Fabrice
authors.initials: F
authors.lastname: Rappaport
authors.affiliation: Department of Molecular Biology and Biotechnology, The University of Sheffield, Sheffield, United Kingdom.
authors.forename: Robert K
authors.initials: RK
authors.lastname: Poole
authors.affiliation: Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russian Federation.
authors.forename: Vitaliy B
authors.identifier: 0000-0002-3400-9068
authors.initials: VB
authors.lastname: Borisov
mesh_terms: D003573:Cytochrome b Group; D003580:Cytochromes / Q000378:metabolism*; D004579:Electron Transport; D045222:Electron Transport Chain Complex Proteins / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000378:metabolism*; D006418:Heme / Q000378:metabolism*; D010088:Oxidoreductases / Q000378:metabolism*
chemical_list: D003573:Cytochrome b Group; D003580:Cytochromes; D045222:Electron Transport Chain Complex Proteins; D029968:Escherichia coli Proteins; D006418:Heme; D010088:Oxidoreductases; C040077:cytochrome bd terminal oxidase complex, E coli