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:28844695). Part of the enzyme membrane arm which is embedded in the lipid bilayer and involved in proton translocation (PubMed:28844695). . This is the function of MT-ND4L (mitochondrially encoded NADH:ubiquinone oxidoreductase core subunit 4L, ENSG00000212907).