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:30922174, PubMed:22036843). Essential for the catalytic activity of complex I (PubMed:30922174, PubMed:22036843). Essential for the 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 (PubMed:30922174). 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 (PubMed:12611891). Interacts with NDUFAF3 (PubMed:19463981). Interacts with NDUFAF7 (PubMed:20406883, PubMed:24089531). 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 (PubMed:24089531, PubMed:24838397). The disease is caused by variants affecting the gene represented in this entry. Belongs to the complex I 49 kDa subunit family.