Question

You have perfected a procedure in which the two enzyme complexes pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase can be dissociated into their individual subunits and the subunits then reassembled into “holoenzymes.” Which protein subunit could be “swapped” between pyruvate dehydrogenase and alpha-keto glutarate dehydrogenase without loss of activity to either reconstituted enzyme when each of the enzyme complexes is provided with its appropriate substrate?

	A.	Thiamine pyrophosphate, because the first step in each of the reactions is a decarboxylation.
	B.	E3, because it catalyzes the last step in the reactions of pyruvate dehydrogenase as well as alpha-ketoglutarate dehydrogenase, using the same reactants and forming the same products.
	C.	Lipoic Acid, because it facilitates both decarboxylation and oxidation
	D.	Coenzyme A, because it is a participant in all the steps in oxidative decarboxylation
	E.	All these protein subunits could be exchanged between pyruvate dehydrogenase and alpha-keto glutarate dehydrogenase