ABSTRACT
The biogeochemical cycling of the basic elements for life including carbon, nitrogen, oxygen, and sulfur, has attracted the interest of many researchers over the past decades in view of its importance for the earth with a rapidly growing population, and in view of its impact on our environment and climate [1]. Of similar importance, the biogeochemistry of the essential transition metals has been extensively studied because of their function as cofactors, or as part of cofactors in enzymes, and as structural elements in proteins. Note that metalloproteins comprise one third to half of all known proteins. Many essential life processes, including photosynthesis, respiration, nitrogen fixation, strictly depend on transition metal ions and their ability to catalyze multi-electron 2transformations. Other essential life processes, such as proteolysis and the equilibration of carbon dioxide and bicarbonate are hydrolytic transformations that are also catalyzed by metalloenzymes [2]. The essential transition metal ions for terrestrial organisms include vanadium to zinc of the first-row transition metal series and molybdenum and tungsten in the second- and third-row series.
