This family contains the eukaryotic NADH:ubiquinone oxidoreductase subunit B14.5a (Complex I-B14.5a) (EC:1.6.5.3). This is approximately 100 residues long, and forms part of a multiprotein complex that resides on the inner mitochondrial membrane. The main function of the complex is the transport of electrons from NADH to ubiquinone, accompanied by translocation of protons from the mitochondrial matrix to the intermembrane space.