Core subunit of the mitochondrial membrane respiratory chain NADH dehydrogenase (Complex I) which catalyzes electron transfer from NADH through the respiratory chain, using ubiquinone as an electron acceptor (PubMed:18721790, PubMed:10852722). Essential for the catalytic activity and assembly of complex I (By similarity). a ubiquinone + 5 H(+)(in) + NADH = a ubiquinol + 4 H(+)(out) + NAD(+) Core subunit of respiratory chain NADH dehydrogenase (Complex I) which is composed of 45 different subunits (PubMed:10852722, PubMed:18721790, PubMed:25209663). Interacts with NDUFAF3 (By similarity). Interacts with RAB5IF (By similarity). Found in subcomplexes containing subunits NDUFS2, MT-ND1 and NDUFA13 (By similarity). Belongs to the complex I 30 kDa subunit family.