Rubredoxins are small, iron-containing non-heme proteins that play an important role in biological electron transfer processes, particularly in anaerobic and microaerophilic organisms. They are among the simplest known iron–sulfur proteins and typically consist of a single iron atom coordinated by four cysteine sulfur atoms in a nearly tetrahedral geometry. Unlike other iron–sulfur proteins such as ferredoxins, rubredoxins do not contain inorganic sulfide; instead, the metal center is stabilized solely by thiolate ligands from the protein backbone. The iron in rubredoxins cycles reversibly between the ferric (Fe³⁺) and ferrous (Fe²⁺) oxidation states, enabling