This family consists of the NADH-ubiquinone oxidoreductase B12 subunit proteins. NADH is the central source of electrons in the mitochondrial and bacterial respiration. NADH-ubiquinone oxidoreductase is involved in the transfer of electrons from NADH to the electron transport chain. This oxidation of NADH is coupled to proton transfer across the membrane, generating a proton motive force that is utilized for the synthesis of ATP. The function of this subunit is unclear.