<p> NADH:ubiquinone oxidoreductase (complex I) (<db_xref db="EC" dbkey="1.6.5.3"/>) is a respiratory-chain enzyme that catalyses the transfer of two electrons from NADH to ubiquinone in a reaction that is associated with proton translocation across the membrane (NADH + ubiquinone = NAD+ + ubiquinol) [<cite idref="PUB00005074"/>]. Complex I is a major source of reactive oxygen species (ROS) that are predominantly formed by electron transfer from FMNH(2). Complex I is found in bacteria, cyanobacteria (as a NADH-plastoquinone oxidoreductase), archaea [<cite idref="PUB00043561"/>], mitochondira, and in the hydrogenosome, a mitochondria-derived organelle. In general, the bacterial complex consists of 14 different subunits, while the mitochondrial complex contains homologues to these subunits in addition to approximately 31 additional proteins [<cite idref="PUB00045437"/>]. Mitochondrial complex I, which is located in the inner mitochondrial membrane, is the largest multimeric respiratory enzyme in the mitochondria, consisting of more than 40 subunits, one FMN co-factor and eight FeS clusters [<cite idref="PUB00045438"/>]. The assembly of mitochondrial complex I is an intricate process that requires the cooperation of the nuclear and mitochondrial genomes [<cite idref="PUB00045438"/>, <cite idref="PUB00045439"/>]. Mitochondrial complex I can cycle between active and deactive forms that can be distinguished by the reactivity towards divalent cations and thiol-reactive agents. All redox prosthetic groups reside in the peripheral arm of the L-shaped structure. The NADH oxidation domain harbouring the FMN cofactor is connected via a chain of iron-sulphur clusters to the ubiquinone reduction site that is located in a large pocket formed by the PSST and 49kDa subunits of complex I [<cite idref="PUB00045440"/>].</p><p>This entry describes the F subunit of complexes that resemble NADH-quinone oxidoreductases. The electron acceptor is a quinone, ubiquinone, in mitochondria and most bacteria, including <taxon tax_id="562">Escherichia coli</taxon>, where the recommended gene symbol is nuoF. This family does not have any members in chloroplast or cyanobacteria, where the quinone may be plastoquinone and NADH may be replaced by NADPH, nor in Methanosarcina, where NADH is replaced by F420H2. </p><p>This entry represents the iron-sulphur binding domain of the F subunit.</p> NADH ubiquinone oxidoreductase, F subunit, iron sulphur binding