Final answer:
Out of the given citric acid cycle enzymes, malate dehydrogenase is the one that is not subject to allosteric regulation, as it follows classic enzyme kinetics.
Step-by-step explanation:
Among the citric acid cycle enzymes, isocitrate dehydrogenase and α-ketoglutarate dehydrogenase are subject to allosteric regulation, which is influenced by the cellular energy status such as ATP, NADH, and succinyl-CoA levels. Pyruvate dehydrogenase is also allosterically regulated and is further controlled by phosphorylation. However, malate dehydrogenase and fumarate hydratase are not traditionally known to be allosterically regulated. Specifically, malate dehydrogenase is not allosterically regulated but follows classic enzyme kinetics. Therefore, the enzyme from the options provided that is not subject to allosteric regulation is C) malate dehydrogenase.