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. Binds 1 Fe(3+) ion per subunit. Extremely thermostable, being unaffected after incubation for 24 hours at 95 degrees Celsius. Belongs to the rubredoxin family.