The equilibrium constant for the reaction catalyzed by malate dehydrogenase (malate to
oxaloacetate) is about 5.9 × 10−6. Which of the following best describes the situation in which
malate is converted to oxaloacetate during the citric acid (Krebs) cycle?
a. The next reaction of the cycle, citrate synthase, is highly exergonic and it pulls the
malate dehydrogenase reaction forward by removing oxaloacetate.
b. The reaction is exergonic under standard conditions in the direction of the citric acid
cycle and this drives the reaction.
c. Malate accumulates in the cell to such a high concentration that it pushes the reaction
forward.
d. Malate dehydrogenase changes the equilibrium constant for the reaction, allowing it to
proceed rapidly.
e. Malate dehydrogenase catalyzes an irreversible reaction in the citric acid cycle.