BSCI 426/ Biol 622     Fall ‘14                           Problem Set 7

assigned:     10/23/14
due:           10/30/14

Insight into the ATP synthase

1. In the model of the ATP synthase discussed in class, the rotor contained 12 "c" subunits. What was the stoichiometry of the pump? (i.e. proton transported per ATP synthesized)

2. If the number of "c" subunits were 9, what would be the stoichiometry?

3. If the free energy change to synthesize ATP were 50 kJ/mole, what would be the minimum amount of energy in the proton gradient that would be needed in order to synthesize ATP for the 2 cases in problem 1 and 2 above?

4. If in problem "3" you were given that the change in pH across the membrane was 1.0 (high pH on the F1 side of the membrane), what would be the value of the membrane potential in each of the 2 cases?

5. If the ATP synthase in problem 1 were reconstituted into phospholipid vesicles such that the F1 portion faced the outer compartment and then ATP were added to the external medium, what would happen? (Assume that protons cannot cross the membrane except through the ATP synthase.The aqueous solutions have 1 mM buffer)

6. What would happen if you repeated problem 5 but in the presence of nigericin (with 100 mM KCl, 1 mM buffer on each side of the vesicle membrane).  What if you had valinomycin present instead of nigericin?

7. Repeat problem 5 except that now both the 12-c-subunit synthase and the 9-c-subunit synthase are present in the SAME vesicle membrane and in the same orientation.