Zinc enzymes.

The number of zinc enzymes for which detailed structural and mechanistic data, including high resolution crystal structures, are available is increasing rapidly. The new findings continue to support the conclusion that the majority of zinc enzymes catalyze hydrolysis or closely related transfer reactions. In a protein environment, tetrahedral or 5-coordinate Zn2+ is ideally suited to activate a coordinated water (frequently a Zn2+--OH) as a nucleophile attacking the carbonyl carbon of a peptide bond, the carbon of carbon dioxide or the phosphorus of a phosphate ester. Protein-bound Zn2+ can function catalytically by forming mixed complexes with the substrate, either by expanding its coordination sphere or by exchanging a ligand. Formation of protein-Zn2+-substrate bonds can position the substrate or polarize its electron distribution to facilitate further steps in the reaction.