Antimony and Bismuth
Antimony and bismuth are in Group 15 of the periodic table. They display important impacts on biological systems and are being used as components of anti-parasitic, antimicrobial or anti-cancer drugs. In this chapter, the general scenarios of binding and transport of antimony (as Sb(III) and Sb(V)) and bismuth (as Bi(III)) in biological systems are summarized. Both can be biomethylated by different mechanisms, including enzymatic catalysis. Antimonate (Sb(V)) can be reduced to the more toxic antimonite (Sb(III)), both enzymatically and non-enzymatically. Sb(III) transporters are ubiquitously present in organisms as aquaglyceroporin protein channels. To acquire resistance to antimony, organisms rely on several protein systems that extrude intracellular antimony. Selected antimony-binding proteins have been identified and structurally characterized and more can be identified by proteomic approaches. Binding of Bi(III) to proteins and enzymes offers information on transport of the metal ions in biological systems. Further work is required to uncover their medicinal potentials as well as understand their toxicity.