Question

15. The Turnover Number of Carbonic Anhydrase Carbonic anhydrase of erythrocytes (Mr 30,000) has one of the highest turnover numbers known. It catalyzes the reversible hydration of CO2: H2O 1 CO2 Δ H2CO3 This is an important process in the transport of CO2 from the tissues to the lungs. If 10.0 [1]g of pure carbonic anhydrase catalyzes the hydration of 0.30 g of CO2 in 1 min at 37 8C at Vmax, what is the turnover number (kcat) of carbonic anhydrase (in units of min

Answer 1

Turnover number= Kcat = Vmax/ Concentration of enzyme

Vmax = Moles of CO2 hydrolyzed / second

Moles of CO2 hydrolyzed = Mass of CO2 / Molar mass of CO2 = 0.30 / 44 = 0.00682 moles

Moles of CO2 hydrolyzed per minute = 0.00682

So moles of CO2 hydolyzed per second = 0.00682 / 60 = 1.137 X 10^-4 moles / second = Vmax

Moles of enzyme = Mass / Molar mass = 10.0 [micro]g / 30000 = 3.333 X 10^-10 moles

Kcat = 1.137 X 10^-4 moles / 3.333 X 10^-10 moles = 0.3411 X 10⁶ per second = 0.3411 X 60 X 10⁶ per minute

= 20.466 X 10⁶ per minute