Carbonic Anhydrase (Bio-Inorganic Chemistry)

Carbonic Anhydrase

*It is a zinc enzyme that catalyses the hydration of co2 and dehydration of HCO3-.
* The enzyme can hydrate 10^6 molecules of co2 per second at 30 degree celsius .
Which is 10^7 times faster than the uncatalysed rate of hydration of co2.
Carbonic anhydrase with a molar mass of about 30000 occurs in animals as well as plants.

(His- Histidine Unit)

*Epo enzyme binded with metal ion

*The zinc ion lies in a deep pocket created by coiled enzyme and is coordinated with three nitrogen atom of three imidazole ring of histidine groups of the epoenzyme.

*The 4th coordination site is perhaps occupied by a water molecule  when the enzyme is at rest.

*The stereochmistry of zinc in the enzyme is tetrahedral.

*The lewis acidity of zn2+ ion in carbonic unhydrate polarizes the coordinated H2O molecule to the point of loss of H+ ion to form coordinated OH group.

(Probable mechanism for reversible hydration of Co2)

*It is a hydroxy form of enzyme. which is believed to reversibly hydrate Co2 to HCO3-

*Catalyst reversible hydration of Co2 is a close loop.

*The clockwise cycle shows a Co2 to HCO3- and the anticlock wise cycle shows the relese of Co2 from HCO3-.