Cell membranes provide compartmentalization and allow cells to keep their physical-chemistry balance. Ion transport across cell membranes is vital for life, establishing and maintaining a difference of electrochemical potential. From the biosynthesis of energy to the transport of solutes, ion transport is central to the energy transduction process.One of key players in the energy transduction process is the respiratory Complex I (NADH:ubiquinone oxidoreductase. This membrane domain of Complex I has three homologous antiporter subunits where the proton channels are proposed to be located. Recently, new results indicate that Complex I from different bacteria are also able to transport H+ and Na+ in opposite directions. This data prompt the debate on the atomic mechanism behind such antiporter subunits and how such process can be regulated.The aim of this project is to provide the missing piece of behind the antiporter subunits puzzling mechanism. To approach such task two objectives have been draw: a) decipher the mechanism of ion transport of the antiporter subunits of Complex I at atomic level, b) unravel the how the regulation and control of ion transport is performed in Complex I antiporter subunitsTo pursue these objectives a novel sample preparation methodology to perform NMR spectroscopy of membrane proteins will be setup. This experimental setup will combine recent advances in cell-free expression system of membrane proteins with nanodisc technology, providing the antiporter subunits a native membrane like environment to perform solution NMR.To follow ion transport, the antiporter subunits will be selectively isotopic labelled and the NMR spectra will be monitored for changes upon ion transport. These changes will provide a map of the ion channel in the antiporter subunits and how this transport is regulated.