3. Acetylcholinesterase catalyzes the hydrolysis of a neurotransmitter acetylcho

Question

3. Acetylcholinesterase catalyzes the hydrolysis of a neurotransmitter acetylcholine Acetylcholine + H2O acetate + choline The KM of acetylcholinesterase for its substrate is 9 x10 M. In a reaction mixture containing5 nanomoles/mL of acetylcholinesterase and 150 M acetylcholine, a velocity v.-40 mol/mL sec was observed for the acetylcholinesterase reaction. a. Calculate the Vmax for this amount of enzyme b. Calculate the kat for acetylcholinesterase c. Calculate the catalytic efficiency (Kea/K) for acetylcholinesterase d. does this value approach the diffusion control limit?

Explanation / Answer

a. Vmax = (Vo * (Km +[S]))/[S]

Where Vo = 40*10-6 mol/mL.sec

Km = [S] = 9*10-5 M

Vmax = (Vo * (Km +[S]))/[S] = (40*10-6 mol/mL.sec *( 9*10-5 M + 9*10-5 M))/9*10-5 M =40*10-6 *2 mol/mL.sec

Vmax = 80 *10-6 mol/mL.sec

b. Kcat = 5 *10-9 moles/mL / 40*10-6 mol/mL.Sec = 1.25*10-4 sec-1

c. Catalytic Efficiency = Kcat / Km = 1.25*10-4 sec-1/9*10-5 M = 1.38 M-1sec

d. No this value does not approach diffusion control limit

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