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Vectorial proton transfer coupled to reduction of O2 and NO by a heme-copper oxidase
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
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2008 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 105, no 51, 20257-20262 p.Article in journal (Refereed) Published
Abstract [en]

The heme-copper oxidase (HCuO) superfamily consists of integral membrane proteins that catalyze the reduction of either oxygen or nitric oxide. The HCuOs that reduce O2 to H2O couple this reaction to the generation of a transmembrane proton gradient by using electrons and protons from opposite sides of the membrane and by pumping protons from inside the cell or organelle to the outside. The bacterial NO-reductases (NOR) reduce NO to N2O (2NO + 2e + 2H+ → N2O + H2O), a reaction as exergonic as that with O2. Yet, in NOR both electrons and protons are taken from the outside periplasmic solution, thus not conserving the free energy available. The cbb3-type HCuOs catalyze reduction of both O2 and NO. Here, we have investigated energy conservation in the Rhodobacter sphaeroides cbb3 oxidase during reduction of either O2 or NO. Whereas O2 reduction is coupled to buildup of a substantial electrochemical gradient across the membrane, NO reduction is not. This means that although the cbb3 oxidase has all of the structural elements for uptake of substrate protons from the inside, as well as for proton pumping, during NO reduction no pumping occurs and we suggest a scenario where substrate protons are derived from the outside solution. This would occur by a reversal of the proton pathway normally used for release of pumped protons. The consequences of our results for the general pumping mechanism in all HCuOs are discussed.

Place, publisher, year, edition, pages
2008. Vol. 105, no 51, 20257-20262 p.
Keyword [en]
cbb3, flow-flash, nitric oxide, proton pumping, pathway
National Category
Biological Sciences
Research subject
Biochemistry
Identifiers
URN: urn:nbn:se:su:diva-16423DOI: 10.1073/pnas.0805429106ISI: 000261995600045PubMedID: 19074284OAI: oai:DiVA.org:su-16423DiVA: diva2:182943
Available from: 2008-12-18 Created: 2008-12-18 Last updated: 2017-12-13Bibliographically approved
In thesis
1. Proton transfer in nitric oxide reducing heme-copper oxidases
Open this publication in new window or tab >>Proton transfer in nitric oxide reducing heme-copper oxidases
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Heme-copper oxidases (HCuOs) are best known as terminal oxidases in the aerobic respiratory chain, in which they catalyze the reduction of oxygen to water. By receiving protons and electrons from opposite sides of the membrane as well as pumping protons, HCuOs contribute to the electrochemical proton gradient over the membrane that can be used for ATP synthesis. Divergent members of the HCuO superfamily are nitric oxide reductases (NORs) that catalyze the reduction of nitric oxide (NO) to nitrous oxide (N2O) as part of the denitrification process, an alternative respiratory pathway.

The first part of the thesis focuses on electron and proton transfer reactions that are associated with the reductive conversion of NO to N2O and O2 to H2O by the NOR from Paracoccus denitrificans. Our data show that proton uptake in NOR is not electrogenic (protons and electrons are taken up from the same side of the membrane) and that no protons are pumped. Also, structural variants have been investigated and the results suggest a role for these residues in proton transfer. Further, we show that lowering the pH leads to a higher NO reduction rate, while this effect is partially counteracted by a larger degree of substrate inhibition at low pH.

The second part deals with proton transfer and electrical potential generation in the reaction between the cbb3 oxidase from Rhodobacter sphaeroides and O2 or NO. Our data show that NO reduction by cbb3 oxidase is not coupled to proton translocation and that the direction of proton uptake is dependent on substrate. Our findings suggest that the proton pumping mechanism in HCuOs is incompatible with NO reduction intermediates.

Finally, experiments on structural variants of the ba3 oxidase from Thermus thermophilus indicate a functional role for the inspected residues in proton transfer and support the suggestion that a single proton-transfer pathway is used in the ba3 oxidase.

Place, publisher, year, edition, pages
Stockholm: Department of Biochemistry and Biophysics, Stockholm University, 2011. 76 p.
Keyword
heme-copper oxidases, nitric oxide, proton transfer, electron transfer, proton-transfer pathway
National Category
Biochemistry and Molecular Biology
Research subject
Biochemistry
Identifiers
urn:nbn:se:su:diva-62893 (URN)978-91-7447-377-3 (ISBN)
Public defence
2011-11-11, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 14:00 (English)
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Available from: 2011-10-20 Created: 2011-10-03 Last updated: 2011-10-17Bibliographically approved

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