Vectorial proton transfer coupled to reduction of O2 and NO by a heme-copper oxidase
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
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.
cbb3, flow-flash, nitric oxide, proton pumping, pathway
Research subject Biochemistry
IdentifiersURN: urn:nbn:se:su:diva-16423DOI: 10.1073/pnas.0805429106ISI: 000261995600045PubMedID: 19074284OAI: oai:DiVA.org:su-16423DiVA: diva2:182943