Question

Some bacteria can use nitrate as an electron acceptor instead of oxygen, reducing it to nitrite. This requires an enzyme called nitrate reductase.

The reduction and oxidation redox equations I am using are:

NO3- +2H+ +2e- ---> NO2- + H2O

NAD+ + 2H+ +2e- ---> NADH + H+

I calculated the Gibbs free energy change under standard state conditions for the oxidation of NADH by nitrate to be -144.75 kJ/mol. Please use the value to help solve part a.

Please help me with this question as I've been stuck on it for a very long time!!

a. If you assume that all processes operate with 100% efficiency, and that the standard delta G for the synthesis of ATP from ADP and Pi is +35.7 kJmol, what is the theoretical maximum number of ATP molecules that could be synthesized for each molecule of NADH oxidized by nitrate?

b. standard delta G for the oxidation of NADH by O2 is -219 kJ/mol. What is the theoretical maximum number of ATP molecules that could be synthesized for each molecule of NADH oxidized by O2 under standard state conditions? Comment on each energetic difference between oxygen and nitrate respiration.

c. The true number of ATP molecules made for each NADH oxidized by oxygen is about 2.7. How does this number compare to the theoretical maximum that you calculated, and how do you explain the difference?