Quinone oxidoreductase that may play some additional role beyond quinone reduction. Potential redox sensor protein. Overexpression induces retardation of growth. a quinone + H(+) + NADH = a quinol + NAD(+) a quinone + H(+) + NADPH = a quinol + NADP(+) Monomer. Belongs to the NmrA-type oxidoreductase family.