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Gates, AJ 
ORCID: https://orcid.org/0000-0002-4594-5038, Richardson, DJ ORCID: https://orcid.org/0000-0002-6847-1832 and Butt, JN ORCID: https://orcid.org/0000-0002-9624-5226
(2008)
Voltammetric characterization of the aerobic energy-dissipating nitrate reductase of Paracoccus pantotrophus: exploring the activity of a redox-balancing enzyme as a function of electrochemical potential.
Biochemical Journal, 409 (1).
pp. 159-168.
ISSN 0264-6021
Abstract
Paracoccus pantotrophus expresses two nitrate reductases associated with respiratory electron transport, termed NapABC and NarGHI. Both enzymes derive electrons from ubiquinol to reduce nitrate to nitrite. However, while NarGHI harnesses the energy of the quinol/nitrate couple to generate a transmembrane proton gradient, NapABC dissipates the energy associated with these reducing equivalents. In the present paper we explore the nitrate reductase activity of purified NapAB as a function of electrochemical potential, substrate concentration and pH using protein film voltammetry. Nitrate reduction by NapAB is shown to occur at potentials below approx. 0.1 V at pH 7. These are lower potentials than required for NarGH nitrate reduction. The potentials required for Nap nitrate reduction are also likely to require ubiquinol/ubiquinone ratios higher than are needed to activate the H+-pumping oxidases expressed during aerobic growth where Nap levels are maximal. Thus the operational potentials of P. pantotrophus NapAB are consistent with a productive role in redox balancing. A Michaelis constant (KM) of approx. 45 µM was determined for NapAB nitrate reduction at pH 7. This is in line with studies on intact cells where nitrate reduction by Nap was described by a Monod constant (KS) of less than 15 µM. The voltammetric studies also disclosed maximal NapAB activity in a narrow window of potential. This behaviour is resistant to change of pH, nitrate concentration and inhibitor concentration and its possible mechanistic origins are discussed.
| Item Type: | Article |
|---|---|
| Faculty \ School: | Faculty of Science > School of Biological Sciences Faculty of Science > School of Chemistry |
| UEA Research Groups: | Faculty of Science > Research Groups > Biophysical Chemistry (former - to 2017) Faculty of Science > Research Groups > Molecular Microbiology Faculty of Science > Research Groups > Organisms and the Environment Faculty of Science > Research Groups > Chemistry of Light and Energy Faculty of Science > Research Groups > Chemistry of Life Processes Faculty of Science > Research Centres > Centre for Molecular and Structural Biochemistry Faculty of Science > Research Groups > Energy Materials Laboratory |
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| Depositing User: | EPrints Services |
| Date Deposited: | 01 Oct 2010 13:36 |
| Last Modified: | 16 May 2023 00:32 |
| URI: | https://ueaeprints.uea.ac.uk/id/eprint/196 |
| DOI: | 10.1042/BJ20071088 |
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