Ferredoxins have low weight molecularly, acidic, soluble iron-sulfur proteins that are found in a variety of organisms, and acts as a multi-functional electron carrier in varied redox structures.

Proteins that are made of these clusters are exactly as proteins that are transporting these clusters where this iron is partly organized by sulfur. These clusters are replacement groups usually found in varied proteins that contribute to oxidation-reduction catalysis and reactions.

In most examples, this iron is coupled to sulfur(s) from residues of cysteine in “polypeptide backbone” as well as also bound to sulfurs that are inorganic in the ”iron-sulfur” clusters. The main function for these clusters is to expedite electron transmission, while with others, this clusters subsidizes the catalytic function.