ABSTRACT
Life requires an interplay between organic (e.g., proteins, sugars, lipids) and inorganic (e.g., cations, often metals, and anions, such as phosphate) matter. At present, we are aware of at least 13 metals that are essential for plants and animals (Bertini et al. 1994; Lippard and Berg 1994). Four of these, sodium, potassium, magnesium, and calcium, are present in large quantities and are known as bulk metals (Fenton 1995). The remaining nine, which are present in small quantities, are the d-block elements vanadium, chromium, molbydenum, manganese, iron, cobalt, nickel, copper, and zinc, and are known as the trace metals. The bulk metals form 1-2% of the human body weight whereas the trace elements represent less than 0.01%. Even of iron, the most widely used trace metal, we need only in the order of 4−5 grams in a human body (Fenton 1995). The concentrations of metals in the cells are strictly regulated at their respective optimum levels: Too much or too little is often harmful and may even be lethal to the organism. Most of the trace metals are found as natural constituents of proteins. In this way, nature has taken advantage of the special properties of the metal ions and tuned them by protein encapsulation to perform a wide variety of specific functions associated with life processes (Bertini et al. 1994; Lippard and Berg 1994).
