InterPro domain: IPR006138

Among the many polypeptide subunits that make up complex I, there is one with a molecular weight of 20kDa (in mammals) [ 1 ], which is a component of the iron-sulphur (IP) fragment of the enzyme. It seems to bind a 4Fe-4S iron-sulphur cluster. The 20kDa subunit has been found to be nuclear encoded, as a precursor form with a transit peptide in mammals, and in Neurospora crassa. It is mitochondrial encoded in Paramecium (gene psbG) and chloroplast encoded in various higher plants (gene ndhK or psbG).

NADH:ubiquinone oxidoreductase (complex I) ( 7.1.1.2 ) 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) [ 2 ]. 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 [ 3 ], 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 [ 4 ].

1. NADH: ubiquinone oxidoreductase from bovine heart mitochondria. A fourth nuclear encoded subunit with a homologue encoded in chloroplast genomes. FEBS Lett. 301, 237-42
2. The NADH:ubiquinone oxidoreductase (complex I) of respiratory chains. Q. Rev. Biophys. 25, 253-324
3. The respiratory complex I of bacteria, archaea and eukarya and its module common with membrane-bound multisubunit hydrogenases. FEBS Lett. 479, 1-5
4. Assembly of the Escherichia coli NADH:ubiquinone oxidoreductase (complex I). Biochim. Biophys. Acta 1777, 735-9