Zinc is perhaps the most ubiquitous and versatile of all metal cofactors. More than 300 enzymes have a zinc cofactor. Table 4 lists some of the important zinc enzymes. Zinc-binding proteins that engage DNA, the so-called zinc finger proteins, attest to the versatility of zinc in biological systems. Approximately 3% of the genome of mammals codes for zinc finger protein. As a cofactor, zinc can perform both structural and catalytic functions. In carbonic anhydrase, for example, zinc enters into a coordinate bond with the CO2 substrate (Figure 5). In carboxypeptidase, zinc takes an active part in the cleavage of the peptide bond (Figure 6). Multisubu-nit enzymes such as aspartate transcarbamylase use zinc to coordinate the positions of the catalytic and regulatory subunits, a structural role. Cu2,Zn2 superoxide dismutase requires zinc to position the copper atom in the channel accessed by the substrate HO'2, another structural role. In zinc finger proteins, Zn2+ contributes to the stability of the loop structure that contacts the major and minor grooves of DNA. These examples illustrate why zinc is an important companion to enzymes and proteins.

Reactivity Zinc is considered a bland metal because it behaves as a divalent cation with no special geometric preference. It is perhaps this blandness that allows zinc to adapt to so many different enzyme environments. Zinc exists in one

Table 4 Important zinc enzymes




Zn/ protein




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Food Allergies

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