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:10852722, PubMed:18721790). 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 (PubMed:10852722, PubMed:18721790, PubMed:25209663). Component of the iron-sulfur (IP) fragment of the enzyme (PubMed:25209663). Interacts with NDUFAF3 (By similarity). 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.