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:30879903, PubMed:31557978). Essential for catalysing the entry and efficient transfer of electrons within complex I (PubMed:31557978). Plays a key role in the assembly and stability of complex I and participates in the association of complex I with ubiquinol-cytochrome reductase complex (Complex III) to form supercomplexes (PubMed:30879903, PubMed:31557978). a ubiquinone + 5 H(+)(in) + NADH = a ubiquinol + 4 H(+)(out) + NAD(+) Binds 1 [2Fe-2S] cluster per subunit. Binds 2 [4Fe-4S] clusters per subunit. Core subunit of respiratory chain NADH dehydrogenase (Complex I) which is composed of 45 different subunits (PubMed:12611891). This is the largest subunit of complex I and it is a component of the iron-sulfur (IP) fragment of the enzyme (By similarity). Complex I associates with ubiquinol-cytochrome reductase complex (Complex III) to form supercomplexes (PubMed:30879903, PubMed:31557978). Interacts with MDM2 (PubMed:30879903). Interacts with AKAP1 (By similarity). The disease is caused by variants affecting the gene represented in this entry. Belongs to the complex I 75 kDa subunit family.