Consider the following reactions, which are two consecutive steps in the TCA cycle.
The two reactions are catalyzed by two independent enzymes, malate + NAD + ↔ oxaloacetate + NADH ΔG10 = +29.7 kJ/mol acetyl-CoA + oxaloacetate ↔ citrate + CoA ΔG10 = -31.5 kJ/mol.
How can the first reaction in the list proceed in the direction of products in this pathway with such a high positive free energy change?
a. this reaction is coupled to ATP hydrolysis
b. the second reaction isn the list uses the oxaloacetate keeping its concentration low resulting in a ΔG that is about zero for the first reaction.
c. the Q for the first reaction in the list is much larger than its Keq and as such is irreversible
d. the answer to this question cannot be determined from the information given