Mitochondrial Complex I is the first and largest holoenzyme of the mitochondrial electron transport chain. It oxidizes NADH from the tricarboxylic acid cycle and β oxidation of fatty acids, reduces ubiquinone and transports protons across the inner membrane, contributing to the proton-motive force. It is also involved in the cellular production of reactive oxygen species. Fourteen distinct subunits form the catalytic centers of the enzyme as they are directly involved in transferring electrons from NADH to ubiquinone, or for generation of the membrane potential - they are referred to as the 'core' or 'central' subunits and are conserved from the ancestral enzyme in bacteria to mammals. Seven core subunits are encoded by mtDNA, while the others are encoded the nuclear genome. (Adapted from PMID:23527692 and FBrf0244962.)

NADH:ubiquinone reductase (H(+)-translocating) (7.1.1.2)