Mononuclear Molybdenum-Containing Enzymes

Molybdenum is essential to the great majority of organisms, being found in the active site of prokaryotic and eukaryotic enzymes that catalyze, in general, oxidation–reduction reactions, involving the transfer of an oxygen or sulfur or hydrogen atom. In the mononuclear molybdenum-containing enzymes, the active site harbors one molybdenum ion coordinated by one or two pyranopterin cofactor molecules. The metal coordination sphere is completed by oxygen and/or sulfur and/or selenium atoms, in a diversity of arrangements, that is the base of the classification of these molybdoenzymes into three large families, denominated after one benchmark enzyme: the xanthine oxidase family, the sulfite oxidase family, and the dimethylsulfoxide reductase family. This article provides an overview of the three families of mononuclear-molybdenum containing enzymes, focusing on the structural and mechanistic aspects of the best-characterized members.