NQR complex catalyzes the reduction of ubiquinone-1 to ubiquinol by two successive reactions, coupled with the transport of Na(+) ions from the cytoplasm to the periplasm. NqrA to NqrE are probably involved in the second step, the conversion of ubisemiquinone to ubiquinol. a ubiquinone + H(+) + n Na(+)(in) + NADH = a ubiquinol + n Na(+)(out) + NAD(+) Composed of six subunits; NqrA, NqrB, NqrC, NqrD, NqrE and NqrF. Belongs to the NqrB/RnfD family.