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 (By similarity). Essential for the catalytic activity and assembly of complex I (By similarity). Redox-sensitive, critical component of the oxygen-sensing pathway in the pulmonary vasculature which plays a key role in acute pulmonary oxygen-sensing and hypoxic pulmonary vasoconstriction (By similarity). Plays an important role in carotid body sensing of hypoxia (By similarity). Essential for glia-like neural stem and progenitor cell proliferation, differentiation and subsequent oligodendrocyte or neuronal maturation (By similarity). a ubiquinone + 5 H(+)(in) + NADH = a ubiquinol + 4 H(+)(out) + NAD(+) Binds 1 [4Fe-4S] cluster. Core subunit of respiratory chain NADH dehydrogenase (Complex I) which is composed of 45 different subunits. Component of the iron-sulfur (IP) fragment of the enzyme. Interacts with NDUFAF3. Interacts with NDUFAF7 (By similarity). Interacts with CERS2 (By similarity). Dimethylation at Arg-118 by NDUFAF7 takes place after NDUFS2 assembles into the complex I, leading to stabilize the early intermediate complex. Belongs to the complex I 49 kDa subunit family.