Rubredoxin is a small nonheme, iron protein lacking acid-labile sulfide. Its single Fe, chelated to 4 Cys, functions as an electron acceptor and may also stabilize the conformation of the molecule. Functions as an intermediate component in the electron transfer chain: NADH->NROR->Rd->FprA1/2 in which Rd serves as the proximal electron donor to the FDPs that exhibit H(2)O-forming NADH oxidase activity. Also functions as the proximal electron donor to the Dfx and revRbr proteins that display superoxide reductase (SOR) and NADH peroxidase activity, respectively. 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. Binds 1 Fe(3+) ion per subunit. Up-regulated upon exposure to O(2). Repressed by PerR. Belongs to the rubredoxin family.