Iron-Sulfur clusters are important parts of nearly all electron transfer proteins. The close spatial arrangement of several iron atoms allows for the electron transfer to be fine tuned through different formal oxidation states of the different iron atoms. In the clusters, the iron atoms are connected by sulfur atoms. Cysteinato ligands from the surrounding protein shell complete the coordination sphere.
Iron-Sulfur clusters are found for example in respiratory centers, the photosynthetic centers, nitrogenase and hydrogenase.
They are divided into different structural types according to the number of sulfur and iron atoms they contain: