Biochemistry 4th Edition by Reginald Garrett, Charles Grisham

Exercise 8

Analysis of the NACH-CoQ reductase reaction
a. What is the standard free energy change ( Gº'), for the reduction of coenzyme Q by NADH as carried out by complex I (NADH-coenzyme Q reductase) of the electron transport pathway if
E o'(NAD + /NADH+H + ) = -0.320 V and E o' (CoQ/CoQH2) = +0.060 V.
b. What is the equilibrium constant (K eq ) for this reaction
c. Assume that (1) the actual free energy release accompanying the NADH-coenzyme Q reductase reaction is equal to the amount released under standard conditions (as calculated above), (2) this energy can be converted into the synthesis of ATP with an efficiency = 0.75 (that is, 75% of the energy released upon NADH oxidation is captured in ATP synthesis), and (3) the oxidation of 1 equivalent of NADH by coenzyme Q leads to the phosphorylation of 1 equivalent of ATP. Under these conditions, what is the maximum ratio of [ATP]/[ADP] attainable for oxidative phosphorylation when [Pi] = 1 mM (Assume Gº' for ATP synthesis = +30.5 kJ/mol.)