ABSTRACT
The original definition of a metalloprotein required the metals to be bound so firmly that they are not removed from the protein by the isolation procedure [114]. Inherent to these studies was the determination of the metal type and stoichiometry by some analytical means. The metal was then removed and the apoenzyme examined func tionally to see if the absence of the metal impairs the function of the protein and addition of the metal to the apoenzyme restores the function. While this definition still is reasonable, the modern advances in sequencing and structural analyses have led to identification of potential zinc binding sites without ever determining if the enzyme needs zinc for function. The availability of a putative zinc-binding motif from a structural reference, combined with a family of sequence-related proteins, can lead to prediction of the need for zinc in the function of a protein where this was never suspected (see below).
