Iron-molybdenum-sulfur clusters structure

Figure 10-9. The structure of the unique iron-molybdenum cluster found at the active site of nitro-genase. The molybdenum is co-ordinated to an extremely unusual homocitrate ligand. There is another iron-sulfur cluster close to this site.

The next two entries to Table 3 are cited for completeness. Nitrogenase is treated in Chapter 7 and CO dehydrogenase in Chapter 9. Nitrogenase contains a very complex iron-sulfur cluster that includes another metal, molybdenum or vanadium. The crystal structure of the Mo variant has been determined. There is a third variant, alternative nitrogenase [92], whose cluster apparently does not contain any heterometal. That cluster would thus be a perfect candidate for our definition of a redox-catalytic iron-sulfur cluster. Unfortunately, this third nitrogenase has thus far been characterized to a much lesser extent than the other two forms. For all nitrogenases holds that the binding of N2 to the cluster has not been established [53] therefore, formally these enzymes have not yet been positively identified as redox iron-sulfur catalysts. 

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