The specific metal ion surrounded by ligands in the active site of the enzyme carbonic anhydrase is zinc Zn . This coordination complex enables the enzyme to catalyze the conversion of carbon dioxide CO and water HO into bicarbonate HCO and protons H through a series of steps.1. The zinc ion in the active site is coordinated to three histidine residues of the enzyme and a hydroxide ion OH or water molecule. The coordination of the zinc ion to the histidine residues helps to stabilize the enzyme's structure and position the zinc ion for catalysis.2. The zinc ion polarizes the coordinated hydroxide ion or water molecule, making it more nucleophilic. This means that the oxygen atom in the hydroxide ion or water molecule has a higher electron density, making it more likely to donate a pair of electrons to form a bond with another atom.3. Carbon dioxide CO enters the active site and binds to the zinc ion, displacing the hydroxide ion or water molecule. This binding further polarizes the CO molecule, making the carbon atom more electrophilic and susceptible to nucleophilic attack.4. The nucleophilic hydroxide ion attacks the electrophilic carbon atom of the CO molecule, forming a bond between them. This results in the formation of a bicarbonate ion HCO coordinated to the zinc ion.5. The bicarbonate ion is then released from the active site, and a water molecule replaces it, coordinating to the zinc ion. This resets the enzyme for another round of catalysis.The coordination complex formed by the zinc ion and its ligands in the active site of carbonic anhydrase plays a crucial role in the enzyme's ability to catalyze the conversion of CO and HO into HCO and H. The zinc ion helps to stabilize the enzyme's structure, polarize the hydroxide ion or water molecule, and facilitate the binding and activation of CO, ultimately leading to the formation of bicarbonate and protons.