73 / 103
Page 111
Notes:
conferenceseries
.com
Volume 10, Issue 8 (Suppl)
J Proteomics Bioinform, an open access journal
ISSN: 0974-276X
Structural Biology 2017
September 18-20, 2017
9
th
International Conference on
Structural Biology
September 18-20, 2017 Zurich, Switzerland
Francis Millett, J Proteomics Bioinform 2017, 10:8(Suppl)
DOI: 10.4172/0974-276X-C1-0100
Photoinduced electron transfer in cytochrome bc
1
: Kinetics of ubiquinone transfer from the Q
o
site to
the Q
i
site, and evidence for communication between the monomers in the dimer
Francis Millett
University of Arkansas, USA
T
he electron transfer reactions within wild- type
Rhodobacter sphaeroides
cytochrome bc
1
(cyt bc
1
) were studied using a
ruthenium dimer to rapidly photo oxidize cyt c
1
. It was found that when cyt b
H
was initially reduced before the reaction,
photooxidation of cyt c
1
led to bifurcated reduction of both the iron-sulfur protein and cyt b
L
by QH
2
in the Q
o
site, followed
by re-oxidation of two equivalents of cyt b
L
and cyt b
H
. It was proposed that the newly formed ubiquinone diffused through the
hydrophobic cavity linking the Q
o
site of the reactive monomer A to the Q
i
site of the other monomer B, leading to oxidation
of cyt b
H
in monomer B followed by oxidation of cyt b
L
in monomer A by cross-monomer electron transfer. Addition of one
equivalent of the Q
i
site inhibitor antimycin to the cyt bc
1
dimer had very little effect on any of the electron transfer reactions,
while addition of a second equivalent completely inhibited re-oxidation of cyt b
L
and cyt b
H
. It was also found that addition
of one equivalent of the Q
o
site inhibitor stigmatellin to the cyt bc
1
dimer completely inhibited all electron transfer reactions
in both monomers of the dimer. These experiments are consistent with a half-of-the-sites mechanism in which only one
monomer of the dimer is active at a time, implying monomer-monomer interactions. The rapid electron transfer reaction from
the ISP to cyt c
1
was found to be greatly decreased by viscosity, indicating a multi-step diffusional mechanism as the iron-sulfur
protein rotates from the b state to the c
1
state.
Biography
Francis Millett received his BS in Chemistry from the University of Wisconsin in 1965, his PhD in Chemical Physics from Columbia University in 1970, and was an
NIH Postdoctoral Fellow at California Institute of Technology from 1970-1972. He joined the faculty of the University of Arkansas in 1972, and is now a Distinguished
Professor. He developed, together with Bill Durham, the ruthenium photoreduction method which made it possible to measure the kinetics of key steps in electron
transfer during mitochondrial oxidative phosphorylation. He has directed collaborative, multidisciplinary research which combines rapid kinetics methods, site-
directed mutagenesis, X-ray crystallography, and NMR to investigate protein structure-function relationships.
millett@uark.eduFigure1:
Photoinduced electron transfer in
cytochrome bc1: kinetics of ubiquinone transfer
from the Qo site to the Qi site, and evidence for
communication between the monomers in the
dimer