Iron–sulfur proteins are
proteins characterized by the presence of iron–sulfur clusters containing
sulfide-linked di-, tri-, and tetrairon centers in variable
oxidation states. Iron–sulfur clusters are found in a variety of
metalloproteins, such as the
ferredoxins, as well as
NADH dehydrogenase,
hydrogenases,
coenzyme Q – cytochrome c reductase, succinate – coenzyme Q reductase and
nitrogenase. Iron–sulfur clusters are best known for their role in the
oxidation-reduction reactions of mitochondrial electron transport. Both Complex I and Complex II of
oxidative phosphorylation have multiple Fe–S clusters. They have many other functions including catalysis as illustrated by
aconitase, generation of radicals as illustrated by
SAM-dependent enzymes, and as sulfur donors in the biosynthesis of
lipoic acid and
biotin. Additionally, some Fe–S proteins regulate gene expression. Fe–S proteins are vulnerable to attack by biogenic
nitric oxide. In most Fe–S proteins, the terminal ligands on Fe are thiolate, but exceptions exist.