Question

Malonate is a competitive inhibitor of succinate dehydrogenase. What citric acid cycle intermediates accumulate if malonate is present in a preparation of isolated mitochondria?

a. succinate accumulates
b. a-ketoglutarate accumulates
c. succinyl-CoA accumulates
d. All of the above

Answer 1

Malonate competitively inhibits succinate dehydrogenase in the citric acid cycle, leading to the accumulation of succinate, which cannot be converted into fumarate. correct answer is not given in provided option A

Step-by-step explanation:

When malonate is present, it acts as a competitive inhibitor of succinate dehydrogenase, meaning it competes with succinate for the active site of the enzyme. Since malonate resembles succinate but does not undergo the same dehydrogenation reaction, its binding halts the conversion of succinate to fumarate. This stop in the reaction cascade leads to the accumulation of succinate because it is not being converted to the next intermediate fumarate in the citric acid cycle.

Also, due to the interconnected nature of the citric acid cycle, compounds upstream of succinate may decrease in concentration as they are converted into succinate, while those downstream may not be formed at normal rates. Therefore, the presence of malonate most directly causes succinate to accumulate.