title: Ultrafast photochemistry of the bc1complex.
abstract: We present a full investigation of ultrafast light-induced events in the membraneous cytochrome bc1complex by transient absorption spectroscopy. This energy-transducing complex harbors four redox-active components per monomer: heme c1, two 6-coordinate b-hemes and a [2Fe-2S] cluster. Using excitation of these components in different ratios under various excitation conditions, probing in the full visible range and under three well-defined redox conditions, we demonstrate that for all ferrous hemes of the complex photodissociation of axial ligands takes place and that they rebind in 5-7 ps, as in other 6-coordinate heme proteins, including cytoglobin, which is included as a reference in this study. By contrast, the signals are not consistent with photooxidation of the b hemes. This conclusion contrasts with a recent assessment based on a more limited data set. The binding kinetics of internal and external ligands are indicative of a rigid heme environment, consistent with the electron transfer function. We also report, for the first time, photoactivity of the very weakly absorbing iron-sulfur center. This yields the unexpected perspective of studying photochemistry, initiated by excitation of iron-sulfur clusters, in a range of protein complexes.
authors.affiliation: LOB, Ecole Polytechnique, CNRS, INSERM, 91128 Palaiseau Cedex, France. marten.vos@polytechnique.edu.
authors.forename: Marten H
authors.initials: MH
authors.lastname: Vos
authors.affiliation: School of Biological Sciences, University of Essex, UK.
authors.forename: Brandon J
authors.initials: BJ
authors.lastname: Reeder
authors.affiliation: Department of Biology, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Fevzi
authors.initials: F
authors.lastname: Daldal
authors.affiliation: LOB, Ecole Polytechnique, CNRS, INSERM, 91128 Palaiseau Cedex, France. marten.vos@polytechnique.edu.
authors.forename: Ursula
authors.initials: U
authors.lastname: Liebl