2Fe-2S active sites

Fig. 29.18 (a) The structure (shown in ribbon representation) of Rieske protein from spinach (Spinacia oleraced) chloroplast (PDB code IRFS). The position of the Fe-containing active site is shown, (b) Detail of the [2Fe—2S] active site in which one Fe atom is coordinated by two Cys residues and the second is bound by two His residues. Hydrogen atoms are omitted colour code Fe, green S, yellow C, grey N, blue. 

Although there are three types of active sites in non-heme iron proteins, namely containing one, two, and four iron atoms per center, in the discussion above only tetrameric Fe-S species have been considered. This topic has been treated with some detail because these compounds meet properly the concept of cluster and are therefore clearly within the scope of this book. That is not the case for the di-iron species which form the 2Fe-2S active sites in the ferredoxins nor for the mononuclear center in the rubredoxins. However, in order to get a better understanding of the chemistry of the iron-sulfur proteins, an overview of the chemistry of the 2Fe-2S analogues is also outlined in this Section. 

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