Metalloenzymes

• Metals play roles in approximately one-third of the known enzymes. Metals may be a co-factor or they may be incorporated into the molecule, and these are known as metalloenzymes. 
• Amino Acids in peptide linkage posses groups that can form coordinate-covalent bonds with the metal atom. The free amino and carboxy group bind to the metal affecting the enzymes structure resulting in its active conformation.
• Metals main function is to serve in electron transfer. Many enzymes can serve as electrophiles and some can serve as nucleophilic groups. This versatility explains metals frequent occurrence in enzymes. Some metalloenzymes include hemoglobins, cytochromes, phosphotransferases, alcohol dehydrogenase, arginase, ferredoxin, and cytochrome oxidase.
• Carboxypeptidase A is a zinc metalloenzyme that breaks peptide linkages in the digestion of proteins. The zinc ion that the enzyme contains in its active site plays a key role in that function.

Structure of Fe(III)-peroxo complex, [Fe(TMC)(OO)]+. Hydrogen atoms are omitted for clarity. Key bond distances are shown on the structure. Image Credit: http://www-ssrl.slac.stanford.edu/

Credit:  http://www.cs.stedwards.edu/