Accessory subunit of the mitochondrial membrane respiratory chain NADH dehydrogenase (Complex I), that is believed not to be involved in catalysis. Complex I functions in the transfer of electrons from NADH to the respiratory chain. The immediate electron acceptor for the enzyme is believed to be ubiquinone. Complex I is composed of 45 different subunits. Acetylation of Lys-98 is observed in liver mitochondria from fasted mice but not from fed mice. Lethality around embryonic day 9 (E9). Conditional knockout in the central nervous system does not lead to any visible phenotype until mice reach 10-11 months of age: then mice become lethargic, lose motor control and have difficulty maintaining balance. Defects cause loss of other complex I subunits and reduced NADH dehydrogenase activity. Belongs to the complex I NDUFA5 subunit family.