In some microorganisms, carbon fixation occurs by reversal of the citric acid cycle. This reversal is accomplished in part by the use of a strong reductant (ferredoxin) to drive the alpha-ketoglutarate dehydrogenase reaction in the reductive direction. Part a: ΔG°‘ for reaction as it occurs in the ‘normal’ (oxidative) citric acid cycle is -30.1 kJ/mol. The standard reduction potential for NADH is -0.32 V. In order to drive the reaction in the reverse direction, the reductant (a ferredoxin) must have a lower reduction potential than NADH/NAD+. Remembering that this is a two-electron reduction, and using the numbers given just above, compute the value of the ferredoxin reduction potential that would be needed to make the standard free energy zero (so that the reductive reaction is enegetically just as favorable as the oxidative reaction). Assume that all of the other reactants are the same in the reductive as in the oxidative reaction.

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Chapter1: Biochemistry: An Evolving Science
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Question 1: In some microorganisms, carbon fixation occurs by reversal of the citric acid cycle. This reversal is accomplished in part by the use of a strong reductant (ferredoxin) to drive the alpha-ketoglutarate dehydrogenase reaction in the reductive direction. Part a: ΔG°‘ for reaction as it occurs in the ‘normal’ (oxidative) citric acid cycle is -30.1 kJ/mol. The standard reduction potential for NADH is -0.32 V. In order to drive the reaction in the reverse direction, the reductant (a ferredoxin) must have a lower reduction potential than NADH/NAD+. Remembering that this is a two-electron reduction, and using the numbers given just above, compute the value of the ferredoxin reduction potential that would be needed to make the standard free energy zero (so that the reductive reaction is enegetically just as favorable as the oxidative reaction). Assume that all of the other reactants are the same in the reductive as in the oxidative reaction. Write out the steps in your calculation; i.e., don’t just provide the final number.
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