ABSTRACT
Many metal ions are required for essential functions, yet are toxic in excess. Metalloproteins play important structural and functional roles in cell metabolism. Homeostatic mechanisms maintain a critical balance to avoid toxicity. Such mechanisms must be able to respond to changes in metal concentration in our environment due to diet or environmental pollutants. Maintenance of balance requires regulated absorption, transport, and excretion mechanisms, controlled by a number of genes whose products ensure correct transport of metals to specific sites. Each metal is expected to have its own series of transporters. However, as we will show in the following pages, several metals are highly dependent upon the concentration of other metals. When any gene within the balanced system is nonfunctional, the balance can be upset.
