The [FeS] ferredoxins may be further subdivided into low-potential (bacterial-type) and high-potential (HiPIP) ferredoxins.
Low- and high-potential ferredoxins are related by the following redox scheme:
The formal oxidation numbers of the iron ions can be [2Fe, 2Fe] or [1Fe, 3Fe] in low-potential ferredoxins. The oxidation numbers of the iron ions in high-potential ferredoxins can be [3Fe, 1Fe] or [2Fe, 2Fe].