Iron-molybdenum-sulfur clusters reactions

Unusually for redox reactions involving metal ions, the molybdenum undergoes a two-electron reaction, cycling between Mo and however, the enzymes also have a reactive heme and/or an iron-sulfur cluster (which is a single-electron acceptor/donor). Thus, there must be intermediate formation of Mo (Kisker et al., 1997 Rajagopalan, 1997 Nishino and Okamoto, 2000). 

All known molybdenum- and tungsten-containing enzymes catalyse reduction-oxidation reactions. The oxidation state of the metal centre can vary between iv, v and vi, hence one- and two-electron transfer reaction steps are possible. In Nature two different ways exist to control the catalytic power and the oxidation state of the metal centre of molybdenum enzymes. One is a mononuclear metal centre, which consists of sulfur and oxygen atoms as coordination sphere around molybdenum and the other is the multinuclear metal centre in which the molybdenum is part of an iron-sulfur cluster, which is only known for bacterial nitroge-nase enzymes. ... 

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