title: Respiratory complex I: A dual relation with H(+) and Na(+)?
abstract: Respiratory complex I couples NADH:quinone oxidoreduction to ion translocation across the membrane, contributing to the buildup of the transmembrane difference of electrochemical potential. H(+) is well recognized to be the coupling ion of this system but some studies suggested that this role could be also performed by Na(+). We have previously observed NADH-driven Na(+) transport opposite to H(+) translocation by menaquinone-reducing complexes I, which indicated a Na(+)/H(+) antiporter activity in these systems. Such activity was also observed for the ubiquinone-reducing mitochondrial complex I in its deactive form. The relation of Na(+) with complex I may not be surprising since the enzyme has three subunits structurally homologous to bona fide Na(+)/H(+) antiporters and translocation of H(+) and Na(+) ions has been described for members of most types of ion pumps and transporters. Moreover, no clearly distinguishable motifs for the binding of H(+) or Na(+) have been recognized yet. We noticed that in menaquinone-reducing complexes I, less energy is available for ion translocation, compared to ubiquinone-reducing complexes I. Therefore, we hypothesized that menaquinone-reducing complexes I perform Na(+)/H(+) antiporter activity in order to achieve the stoichiometry of 4H(+)/2e(-). In agreement, the organisms that use ubiquinone, a high potential quinone, would have kept such Na(+)/H(+) antiporter activity, only operative under determined conditions. This would imply a physiological role(s) of complex I besides a simple "coupling" of a redox reaction and ion transport, which could account for the sophistication of this enzyme. This article is part of a Special Issue entitled Respiratory complex I, edited by Volker Zickermann and Ulrich Brandt.
authors.affiliation: Instituto de Tecnologia Química e Biológica, António Xavier, Universidade Nova de Lisboa, Av. da Republica EAN, 2780-157 Oeiras, Portugal.
authors.forename: Paulo J
authors.initials: PJ
authors.lastname: Castro
authors.affiliation: Instituto de Tecnologia Química e Biológica, António Xavier, Universidade Nova de Lisboa, Av. da Republica EAN, 2780-157 Oeiras, Portugal.
authors.forename: Andreia F
authors.initials: AF
authors.lastname: Silva
authors.affiliation: Instituto de Tecnologia Química e Biológica, António Xavier, Universidade Nova de Lisboa, Av. da Republica EAN, 2780-157 Oeiras, Portugal.
authors.forename: Bruno C
authors.initials: BC
authors.lastname: Marreiros
authors.affiliation: Instituto de Tecnologia Química e Biológica, António Xavier, Universidade Nova de Lisboa, Av. da Republica EAN, 2780-157 Oeiras, Portugal.
authors.forename: Ana P
authors.initials: AP
authors.lastname: Batista
authors.affiliation: Instituto de Tecnologia Química e Biológica, António Xavier, Universidade Nova de Lisboa, Av. da Republica EAN, 2780-157 Oeiras, Portugal. Electronic address: mpereira@itqb.unl.pt.
authors.forename: Manuela M
authors.initials: MM
authors.lastname: Pereira
mesh_terms: D004579:Electron Transport; D042967:Electron Transport Complex I / Q000737:chemistry* / Q000648:ultrastructure*; D004789:Enzyme Activation; D008956:Models, Chemical; D056004:Molecular Dynamics Simulation; D010084:Oxidation-Reduction; D011487:Protein Conformation; D017494:Proton Pumps / Q000737:chemistry* / Q000648:ultrastructure*; D011522:Protons; D017382:Reactive Oxygen Species / Q000138:chemical synthesis; D012964:Sodium / Q000737:chemistry*
chemical_list: D017494:Proton Pumps; D011522:Protons; D017382:Reactive Oxygen Species; D012964:Sodium; D042967:Electron Transport Complex I
keywords: Bacteria; Evolution; NADH:quinone oxidoreductase; Respiratory chain; Transport