Carboanhydrases are enzymes that catalyse the hydrolysis of carbon dioxide. These enzymes are involved in many biological
processes such as photosynthesis (CO2 uptake), respiration (CO2 release) and pH control.
The human carboanhydrase, form II(c), consists of 259 amino acids with a molecular weight of around 30 kDa. The
catalytic site contains a Zn2+ ion which is coordinated by three neutral histidine (His) residues and a water
molecule. The water molecule is believed to be important for structural reasons and enzymatic functionality
.In a first step (i), a proton
is transferred to His64 from the coordinated water molecule. In a second step (ii), a buffer molecule (B) coordinates
this proton and transports it away from the active site. The remaining hydroxide ligand reacts quickly
and forms a transition state via hydrogen bonding with CO2 (iii). Following some more transformations,
HCO3- is released as it is replaced by another molecule of water (iv) and (v).
