Urea Transporter/Na+ Exporter (UT/RnfD/NqrB) Superfamily

The Na+ pumping NQR (3.D.5) and RNF (3.D.6) families include protein complexes of six homologous but dissimilar subunits. Two of the six subunits, NqrD and NqrE, and RnfA and RnfD are homologous to each other. However, within 3.D.5 and 3.D.6, only one of the six protein constituents, NqrB and RnfD, respectively, is homologous to Urea Transporters (UT, 1.A.28), and these are believed to be responsible for Na+ transport.