are taken up into organisms by specific transporters and bound to storage proteins such as ferritin or metallothionein when not being used. Cobalt is essential for the functioning of vitamin B12. Main group compounds Many other elements aside from metals are bio-active. Sulfur and phosphorus are required for all life. Phosphorus almost exclusively exists as phosphate and its various esters. Sulfur exists in a variety of oxidation states, ranging from sulfate (SO42−) down to sulfide (S2−). Selenium is a trace element involved in proteins that are antioxidants. Cadmium is important because of its toxicity. See also Physiology Cofactor Iron metabolism References Literature Heinz-Bernhard Kraatz (editor), Nils Metzler-Nolte (editor), Concepts and Models in Bioinorganic Chemistry, John Wiley and Sons, 2006, Ivano Bertini, Harry B. Gray, Edward I. Stiefel, Joan Selverstone Valentine, Biological Inorganic Chemistry, University Science Books, 2007, Wolfgang Kaim, Brigitte Schwederski "Bioinorganic Chemistry: Inorganic Elements in the Chemistry of Life." John Wiley and Sons, 1994, Rosette M. Roat-Malone, Bioinorganic Chemistry : A Short Course, Wiley-Interscience, 2002, J.J.R. Fraústo da Silva and R.J.P. Williams, The biological chemistry of the elements: The inorganic chemistry of life, 2nd Edition, Oxford University Press, 2001, Lawrence Que, Jr., ed., Physical Methods in Bioinorganic Chemistry, University Science Books, 2000, External links The Society of Biological Inorganic Chemistry (SBIC)'s home page The French Bioinorganic Chemistry Society Glossary of Terms in Bioinorganic Chemistry Metal Coordination Groups in Proteins by Marjorie Harding European Bioinformatics Institute MetalPDB: A database of metal sites in biomolecular structures Biochemistry Inorganic chemistry Medicinal inorganic chemistry