Physical & Chemical Properties of Nickel and Its Role

Nickel is a first-row transition metal with chemical and physical characteristics ideally suited to biological activity (18). Divalent nickel is the only oxidation state of nickel that is likely to be of any importance to higher plants. Nevertheless, Ni²⁺ forms a bewildering array of complexes with a variety of coordination numbers and geometries (19). Nickel readily binds, complexes, and chelates a number of substances of biological interest and is ubiquitous in all biological systems. Nickel is now known to be a functional constituent of seven enzymes, six of which occur in bacterial and animal systems, but not known to be active in plants, but the seventh enzyme, urease, is widely distributed in biology. The sensitivity of known biological nickel–complex equilibriums to temperature, concentration, and pH also make nickel an ideal element for the fine control of enzyme reactions (18).