another example: Carbonic Anhydrase

Zn

Active site in  -carbonic anhydrase

Active site and mechanism in  -carbonic anhydrase deprotonation Nucleophilic attack on CO2 Charge stabilization START :B(GLU) H + :B(GLU)

CO 2 --> [CO 3 ] 2- CO 2 --> glucose CO 2 <-- [CO 3 ] 2- glucose --> CO 2 Carbonic Anhydrase is critically important in global C- cycle

CO 2 --> [CO 3 ] 2- CO 2 <-- [CO 3 ] 2- Carbonic Anhydrase important in global C- cycle because catalyzes both directions! Phytoplankton do this: HCO 3 -  CO 2 Diatoms do this: CO 2  HCO 3 - CA importance means these critters are growth limited: when there’s too little Zn, can use Cd and Co!!

Acid/base chemisty in catalysis of Mo enzymes: oxidation of SO 3 2- See in this step how Mo charge affects H2O acidity ditto