Alternative NADH-ubiquinone oxidoreductase which catalyzes the oxidation of mitochondrial NADH does not translocate protons across the inner mitochondrial membrane. a quinone + H(+) + NADH = a quinol + NAD(+) a ubiquinone + H(+) + NADH = a ubiquinol + NAD(+) Binds 1 FAD per subunit. Expressed in seedlings, cotyledons, young leaves, stems and flowers and, to a lower extent, in roots and buds. Follows a circadian regulation; up-regulated in a diurnal manner. Up-regulated by high-light. No visible phenotype. Belongs to the NADH dehydrogenase family.