Molybdenum in living systems

摘要

All forms of life make abundant use of metals available in their environments, and transition metals in particular are put to myriad uses, not least in the active sites of enzymes where the great variety of chemical transformations in which transition metal complexes can participate is harnessed to the metabolic needs of the organism. Although molybdenum lies on the very edge of the "biological" periodic table, it is indispensible to most life forms, and to almost all of the ones with which we are most familiar. The plants and animals upon whom our well-being relies, as well as we ourselves, depend on molybdenum-based chemistry to carry out some of the most important steps in the metabolism of carbon, nitrogen, and sulfur, and many of these transformations constitute critical steps in the global biogeochemical cycles of these elements. Interestingly, and unusually for a transition metal, the biology of molybdenum is based not on the cation Mo~(6+), but instead on the anion MOO_4~(2-). It is the high solubility (and therefore bioavailability) of molybdate that is the principal reason why molybdenum, which is present at only ~1 ppm in the earth's crust, has come to be so broadly distributed in biology. Although occasionally referred to on the basis its role as a metal activator of water as "redox-active zinc", molybdenum is perhaps more appropriately thought of as "redox-active phosphate" on the basis of how it works physiologically.