Catalyzes the NADH-dependent reduction of rubredoxin (Rd). NADPH is a very poor electron donor compared to NADH. Functions as an intermediate component in the electron transfer chain: NADH->NROR->Rd->FprA1/2. Also functions as an intermediate component in the electron transfer chains from NADH to revRbr and Dfx. Therefore, is a key electron carrier in an efficient multienzyme complex that can scavenge O(2) and reactive oxygen species (ROS), and thus plays an important role in the oxidative stress defense system in C.acetobutylicum, an obligate anaerobic bacterium. H(+) + NAD(+) + 2 reduced [rubredoxin] = NADH + 2 oxidized [rubredoxin] Binds 1 FAD per subunit. Monomer. Up-regulated upon exposure to O(2). Repressed by PerR. Is composed of three domains: an FAD-binding domain (residues 2-107 and 223-297), an NADH-binding domain (residues 108-222), and a C-terminal domain (residues 298-379). The disulfide bonds are not involved in the electron transfer from NADH to rubredoxin catalyzed by NROR. Belongs to the FAD-dependent oxidoreductase family.