Biochemistry 4th Edition by Reginald Garrett, Charles Grisham

Exercise 11

Determining the effect of the cytochrome oxidase reaction on oxidative phosphorylation
Write a balanced equation for the reduction of molecular oxygen by reduced cytochrome c as carried out by complex IV (cytochrome oxidase) of the electron transport pathway.
a. What is the standard free energy change ( Gº'), for this reaction if E o'(cytc(Fe3+)/cytc(Fe2+)) = +0.254 V and E o' (1/2 O2/H2O) = +0.816 V.
b. What is the equilibrium constant (Keq) for this reaction
c. Assume that (1) the actual free energy release accompanying cytochrome c oxidation by the electron transport pathway 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 = 0.60 (that is, 60% of the energy released upon cytochrome c oxidation is captured in ATP synthesis), and (3) the reduction of 1 molecule of O₂ by reduced cytochrome c leads to the phosphorylation of 2 equivalents of ATP. Under these conditions, what is the maximum ratio of [ATP]/[ADP] attainable for oxidative phosphorylation when [Pi] = 3 mM (Assume Gº' for ATP synthesis = +30.5 kJ/mol.)