Zinc Plays Both Structural and Catalytic Roles in Metalloproteins

Zinc is bound to the catalytic site of zinc-dependent hydrolases by three amino acid residues, commonly histidines and glutamic acid, and to the structural site of gene transcription regulators by cysteine and histidine. Sitedirected mutagenesis of even one catalytic-site ligand destroys enzyme activity without changing physical properties of the protein, including immunoreactivity. However, nutritional studies demonstrating loss of transcriptional activity upon zinc deprivation have not been reported.