ISBN: 978-83-60043-10-3 - eurobic9

Eurobic9, 2-6 September, 2008, Wrocław, Poland
P150. Enzymatic Electron Transfer in Respiratory Escherichia coli Nitrate
Reductase
A. Parkin a , C. F. Blanford a , J. Weiner b , F. A. Armstrong a
a Inorganic Chemistry, University of Oxford, South Parks Road, OX1 3QR, United Kingdom
b Membrane Protein Research Group, Dept. of Biochemistry, Univ. of Alberta, Edmonton AB T6J 2C2, Canada
We have examined the electrocatalytic properties of mutants of Escherichia coli respiratory nitrate reductase in
order to explore the role of an irregular sequence of reduction potentials in enzymatic electron transfer relays. In
the wild type enzyme, one [4Fe4S] cluster (FS2) located halfway along the electron ‘wire’ in nitrate reductase
has a reduction potential (-420 mV) that is more than 300 mV more negative than its neighbouring clusters
(electron-acceptor FS1 and electron-donor FS3). The electron-transport relay’s potential barriers were
“smoothed out” in two mutants.
By simulating the protein film voltammetry activity of the wild type and mutant nitrate reductases we have been
able to explore the relative importance of distance and potential barriers in limiting the rate of electron transfer in
proteins. We conclude that low potential [4Fe4S] clusters which are also found in DMSO reductase,
quinol:fumarate oxidoreductase and succinate:quinone oxidoreductase (SQR), may be an irreplaceable element
in biological catalysis.
Acknowledgement: UK Engineering and Physical Sciences Research Council (Supergen V).
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