Metalloproteins are often characterized by specific biochemical, functional, and regulatory properties.^1,2  In addition to their characteristic functions in living cells, metal-binding proteins or peptides were found to be useful in fundamental research as well as applied science. The binding of metal ions per se is an important feature because it has been shown that some proteins can be isolated or fractionated by their intrinsic affinity for metal ions.³ 

The purification method is based on the affinity of histidines and, to a lesser extent, cysteines and tryptophans, for divalent cations, such as Cu²⁺, Zn²⁺, Co²⁺, and Ni²⁺.³  This observation was soon developed into one of the most powerful and widely used techniques for protein purification, i.e. immobilized-metal affinity chromatography (IMAC). It was originally applied to the purification of proteins with native affinity for metal ions; such applications of IMAC are still used in proteomic studies.^4–7