InterPro

NADH:ubiquinone oxidoreductase (complex I) (EC: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) [PMID: 1470679]. 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 [PMID: 10940377], mitochondria, 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 [PMID: 18394423].

Image averaging of mitochondrial complex I reveals a complex that can be dissociated into two main sub-complexes. One sub-complex is thought to protrude from the membrane so is to be predominantly in the aqueous phase and contains the binding site for NAD(H), and the input electron transfer chain. The other sub-complex (the hydrophobic protein) is membrane bound, and contains a catalytic site at which ubiquinone is reduced, and inhibitors bind, and several iron sulphur centres [PMID: 9034360].

This entry represents subunit 8 (also known as the ASHI subunit) of the NADH:ubiquinone oxidoreductase beta subcomplex from animals [PMID: 9878551]. This subunit is not believed to be involved in catalysis.