Specific class of high-redox-potential 4Fe-4S ferredoxins. Functions in anaerobic electron transport in most purple and in some other photosynthetic bacteria and in at least one genus (Paracoccus) of halophilic, denitrifying bacteria. E(0) is +330 mV. Homodimer. Belongs to the high-potential iron-sulfur protein (HiPIP) family.