Molybdenum clusters, multinuclear

Molybdenum is found in the active site of nitrogenase as part of a multinuclear cluster with iron (the so-called M-cluster), but in all other enzymes it comprises a mononuclear center (Hille, 1996 Kisker et al., 1997a). The distinguishing characteristic of this latter group of enzymes is that, while other redox-active centers are often present, the molybdenum center itself possesses only a single equivalent of the transition metal. This large and diverse group of enzymes is the subject of the present account. 

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. ... 

---