Question

Of the following enzymes associated with the TCA cycle, which of the following enzymes is not under allosteric regulation?

A) isocitrate dehydrogenase
B) α-ketoglutarate dehydrogenase
C) malate dehydrogenase
D) fumarate hydratase
E) pyruvate dehydrogenase complex

Answer 1

Malate dehydrogenase (C) is the enzyme in the TCA cycle that is not under allosteric regulation, as it is regulated by substrate availability and product concentration.

Step-by-step explanation:

Of the enzymes associated with the TCA cycle, malate dehydrogenase (C) is not under allosteric regulation. The enzymes associated with the TCA cycle that are under allosteric regulation are isocitrate dehydrogenase, α-ketoglutarate dehydrogenase, and malate dehydrogenase. All three of these enzymes are regulated by various factors such as NADH, ATP, and calcium. However, fumarate hydratase is not under allosteric regulation.

Enzymes in the TCA cycle such as isocitrate dehydrogenase, α-ketoglutarate dehydrogenase, and pyruvate dehydrogenase complex are regulated allosterically by various molecules that signal the energy status of the cell. NADH, ATP, and succinyl-CoA serve as inhibitors for several of these enzymes, while ADP and calcium may serve as activators. In contrast, malate dehydrogenase does not exhibit allosteric regulation but is instead regulated by the availability of its substrates and the concentration of products like NADH.