title: Sodium influence on energy transduction by complexes I from Escherichia coli and Paracoccus denitrificans.
abstract: The nature of the ions that are translocated by Escherichia coli and Paracoccus denitrificans complexes I was investigated. We observed that E. coli complex I was capable of proton translocation in the same direction to the established deltapsi, showing that in the tested conditions, the coupling ion is the H(+). Furthermore, Na(+) transport to the opposite direction was also observed, and, although Na(+) was not necessary for the catalytic or proton transport activities, its presence increased the latter. We also observed H(+) translocation by P. denitrificans complex I, but in this case, H(+) transport was not influenced by Na(+) and also Na(+) transport was not observed. We concluded that E. coli complex I has two energy coupling sites (one Na(+) independent and the other Na(+) dependent), as previously observed for Rhodothermus marinus complex I, whereas the coupling mechanism of P. denitrificans enzyme is completely Na(+) independent. This work thus shows that complex I energy transduction by proton pumping and Na(+)/H(+) antiporting is not exclusive of the R. marinus enzyme. Nevertheless, the Na(+)/H(+) antiport activity seems not to be a general property of complex I, which may be correlated with the metabolic characteristics of the organisms.
authors.affiliation: Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av. de Republica EAN, 2780-157 Oeiras, Portugal.
authors.forename: Ana P
authors.initials: AP
authors.lastname: Batista
authors.forename: Manuela M
authors.initials: MM
authors.lastname: Pereira
mesh_terms: D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D042967:Electron Transport Complex I / Q000378:metabolism*; D004734:Energy Metabolism / Q000187:drug effects*; D004926:Escherichia coli / Q000187:drug effects / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008564:Membrane Potentials / Q000187:drug effects; D009243:NAD / Q000378:metabolism*; D010088:Oxidoreductases / Q000378:metabolism; D010101:Oxygen Consumption; D010231:Paracoccus denitrificans / Q000187:drug effects / Q000378:metabolism*; D011522:Protons; D045245:Rhodothermus / Q000378:metabolism; D012964:Sodium / Q000494:pharmacology*
chemical_list: D011522:Protons; D009243:NAD; D012964:Sodium; D010088:Oxidoreductases; D042967:Electron Transport Complex I