title: Photo-induced dynamics of the heme centers in cytochrome bc₁.
abstract: The ultrafast response of cytochrome bc1 is investigated for the first time, via transient absorption spectroscopy. The distinct redox potentials of both c1- and b-hemes allow for a clear differentiation of their respective signals. We find that while the c1-heme photo-product exhibits the characteristics of a 5-coordinated species, the b-hemes presumably undergo photo-oxidation at a remarkably high quantum yield. The c1-heme iron-ligand recombination time is 5.4 ps, in agreement with previous reports on homologous cytochromes. The suggested photo-oxidized state of the b-hemes has a life-time of 6.8 ps. From this short life-time we infer that the electron acceptor must be within van der Walls contact with the heme, which points to the fact that the axial histidine residue is the electron acceptor. The different heme-responses illustrate the flexibility of the c1-heme ligation in contrast to the more rigid b-heme binding, as well as the higher electronic reactivity of the b-hemes within the bc1 complex. This study also demonstrates the remarkable connection between the heme local environment and its dynamics and, therefore, biological function.
authors.affiliation: Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratoire de Spectroscopie Ultrarapide, ISIC, Faculté des Sciences de Base, Station 6, 1015 Lausanne, Switzerland. majed.chergui@epfl.ch.
authors.forename: Adrien A P
authors.initials: AA
authors.lastname: Chauvet
authors.forename: André
authors.initials: A
authors.lastname: Al Haddad
authors.forename: Wei-Chun
authors.initials: WC
authors.lastname: Kao
authors.forename: Frank
authors.initials: F
authors.lastname: van Mourik
authors.forename: Carola
authors.initials: C
authors.lastname: Hunte
authors.forename: Majed
authors.initials: M
authors.lastname: Chergui
mesh_terms: D014450:Electron Transport Complex III / Q000737:chemistry*; D006418:Heme / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D008027:Light
chemical_list: D006418:Heme; D014450:Electron Transport Complex III