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-64 and Lys-75 is observed in liver mitochondria from fasted mice but not from fed mice. Belongs to the complex I NDUFA2 subunit family.