Some of the more interesting elements in the chemistry of life are less commonly occuring ones such as nickel and molybdenum. This volume elucidates the chemistry of these elements in important enzymes and also explores the chemistry of elements that do not normally occur in biological molecules, but are useful in probing their structure and function. Topics include: Acquisition and transport of Ni. Mechanistic action of Ni in a wide variety of enzymes. Multielectron redox systems involving pterins in proteins. Chemistry of the pterin and flavin complexes of Mo, Fe, Cu and Ru ions. Replacement of iron in transferrin by a number of other metal ions. Use of polypyridyl complexes of ruthenium and other transition metals as probes of nucleic acid structure through phohemical reactions.