The Nature of Molybdenum and Tungsten Centres in Oxo-transfer Enzymes

In a perspective provided by structure of the Periodic Table, molybdenum and tungsten are distinct in being the only 4d- and 5d-transition metals that are required for the normal metabolism of biological systems. These metals play a vital role as the catalytic centres of a wide variety of enzymes. Mo was first identified as an essential trace element in the 1930s, because of its role in nitrogen fixation this metal is now known to be the catalytic centre of over 50 enzymes. Evidence for the involvement of W in biological systems has been obtained only relatively recently, especially for enzymes of hyperthermophilic archea that thrive near lOOX.  

There are (at least) two striking parallels between the nature and function of Mo and W centres in enzymes. First, the net effect of the catalysis effected by virtually all of these enzymes is the transfer of an oxygen atom to, or from, the substrate - with the metal undergoing a concomitant redox change from M to M or vice versa (1). 

The Nature of Molybdenum and Tungsten Centres in Oxo-transfer Enzymes 

Despite the above important common denominators, and the similar size and chemical properties of chemically equivalent W and Mo species, important differences have evolved in the biological roles of these two metals. Two particular points highlight these differences (i) the significance of these metals for nitrogen fixation (ii) the prevalence of Mo over W as the catalytic centre of oxo-transfer enzymes. 

Sulfite Oxidase Nitrate Reductase DMSO Reductase 

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