Question

Of the dehydrogenase reactions in glycolysis and the TCA cycle, all but one use NAD+ as the electron acceptor. The exception is succinate dehydrogenase which uses covalently bound FAD as the electron acceptor. What is the standard free energy change (DGo’) for this reaction if Eo’ (fum/succ) = +0.031 V and Eo’ (O2/H20) = +0.816. What is the Keq for this reaction? Assuming that 1) the actual free energy release when NADH is oxidized by the electron transport chain is equal to the standard conditions as calculated above, 2) that this energy can be converted into the synthesis of ATP with an efficiency of 70%, and 3) the oxidation of 1 NADH leads to the phosphorylation of 2 equivalents of ATP; what is the maximum ratio of [ATP]/[ADP] attainable by oxidative when [Pi] = 1mM?

Answer 1

E₀(O2/H2O)= 0.816 V and E₀(fum/succ)= 0.031 V so E = 0.816-0.031= 0.785  

and  

finally here n=2 fum/succ couple

or Keq= 3.61

After assuming the actual energy release when NADH is oxidized by the electron transport chain is equal to the standard energy change.