One of at least two accessory proteins for anaerobic nitric oxide (NO) reductase. Reduces the rubredoxin moiety of NO reductase. H(+) + NAD(+) + 2 reduced [nitric oxide reductase rubredoxin domain] = NADH + 2 oxidized [nitric oxide reductase rubredoxin domain] Nitrogen metabolism; nitric oxide reduction. Submicromolar concentrations of NO induce anaerobic expression. Repressed by oxygen in the presence of NO. Belongs to the FAD-dependent oxidoreductase family.