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:27799543, PubMed:32072193). Essential for catalysing the entry and efficient transfer of electrons within complex I (PubMed:27799543). 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:27799543). 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 (By similarity). 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:27799543). In astrocytes, less complex I is assembled into supercomplexes as compared to neurons (PubMed:27799543). Interacts with MDM2 (By similarity). Interacts with AKAP1 (PubMed:32072193). Brain. More abundant in neurons than in astrocytes (at protein level). Acetylation of Lys-84 is observed in liver mitochondria from fasted mice but not from fed mice. Belongs to the complex I 75 kDa subunit family.