The metal ion at the active site of the enzyme carbonic anhydrase is zinc Zn . It plays a crucial role in facilitating the conversion of carbon dioxide CO into bicarbonate HCO and a proton H .The mechanism of this conversion involves the following steps:1. A water molecule binds to the zinc ion at the active site of carbonic anhydrase, forming a zinc-bound hydroxide ion Zn-OH .2. The zinc-bound hydroxide ion acts as a nucleophile, attacking the carbon dioxide molecule that enters the active site. This results in the formation of a zinc-bound bicarbonate ion Zn-HCO .3. The zinc-bound bicarbonate ion then dissociates from the enzyme, releasing the bicarbonate ion HCO into the surrounding solution.4. Another water molecule binds to the zinc ion, regenerating the zinc-bound hydroxide ion and allowing the enzyme to catalyze the reaction again.The presence of the zinc ion at the active site of carbonic anhydrase lowers the activation energy of the reaction, enabling the rapid interconversion of CO and HCO in biological systems. This process is essential for maintaining acid-base balance in the body and facilitating the transport of CO in the form of bicarbonate ions in the blood.