Catalytic Protein Film Voltammetry from a Respiratory Nitrate Reductase Provides Evidence for Complex Electrochemical Modulation of Enzyme Activity†

Anderson, Lee J., Richardson, David and Butt, Julea (2001) Catalytic Protein Film Voltammetry from a Respiratory Nitrate Reductase Provides Evidence for Complex Electrochemical Modulation of Enzyme Activity†. Biochemistry, 40 (38). pp. 11294-11307.

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Abstract

The first step in the respiratory reduction of nitrate to dinitrogen in Paracoccus pantotrophus is catalyzed by the quinol-nitrate oxidoreductase NarGHI. This membrane-anchored protein directs electrons from quinol oxidation at the membrane anchor, NarI, to the site of nitrate reduction in the membrane extrinsic [Fe-S] cluster and Mo-bis-MGD containing dimer, NarGH. Liberated from the membrane, NarGH retains its nitrate reductase activity and forms films on graphite and gold electrodes within which direct and facile exchange of electrons between the electrode and the enzyme occurs. Protein film voltammetry has been used to define the catalytic behavior of NarGH in the potential domain and a complex pattern of reversible, nitrate concentration dependent modulation of activity has been resolved. At low nitrate concentrations the local maximum observed in the catalytic current-potential profile reveals how NarGH can catalyze nitrate reduction via two pathways having distinct specificity constants, kcat obs/KM obs. Catalysis is directed to occur via one of the pathways by an electrochemical event within NarGH. On increasing the nitrate concentration, the local maximum in the catalytic current becomes less distinct, and the catalytic waveform adopts an increasingly sigmoidal form. A pattern of voltammetry similar to that observed during nitrate reduction is observed during reduction of the stereochemically distinct substrate chlorate. Centers whose change of oxidation state may define the novel catalytic voltammetry of NarGH have been identified by EPR-monitored potentiometric titrations and mechanisms by which the electrochemistry of Mo-bis- MGD or [Fe-S] clusters can account for the observed behavior are discussed.

Item Type: Article
Faculty \ School: Faculty of Science > School of Chemistry
Faculty of Science > School of Biological Sciences
University of East Anglia > Faculty of Science > Research Groups > Biophysical Chemistry
University of East Anglia > Faculty of Science > Research Groups > Molecular Microbiology
University of East Anglia > Faculty of Science > Research Groups > Organisms and the Environment
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Depositing User: Rachel Smith
Date Deposited: 15 Feb 2011 13:17
Last Modified: 25 Jul 2018 07:36
URI: https://ueaeprints.uea.ac.uk/id/eprint/21423
DOI: 10.1021/bi002706b

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