Alternative, nonproton pumping NADH:quinone oxidoreductase that delivers electrons to the respiratory chain by oxidation of NADH and reduction of quinones (By similarity). Utilizes NADH exclusively, and electron flow from NADH to ubiquinone does not generate an electrochemical gradient (By similarity). a quinone + H(+) + NADH = a quinol + NAD(+) a ubiquinone + H(+) + NADH = a ubiquinol + NAD(+) Binds 1 FAD per subunit. Membrane-bound (By similarity). Interaction with the membrane is probably mediated by amphipathic helices and electrostatic interactions (By similarity). Belongs to the NADH dehydrogenase family.