Acetyl-CoA is transported out of the mitochondria in order to serve as a substrate for fatty acid or cholesterol synthesis. Which of the following enzymes used in this transport process provides a cofactor required for these reductive biosynthesis reactions?

Question

Quizplus · Accepted Answer

Malic enzyme generates NADPH, a cofactor required for reductive biosynthesis reactions such as fatty acid and cholesterol synthesis.  Acetyl-CoA enters the cytoplasm in the form of citrate via the tricarboxylate transport system (see Figure 19-3). In the cytoplasm, citrate is converted to oxaloacetate and acetyl-CoA by the ATPdriven ATP-citrate lyase (ACL) reaction. This reaction is essentially the reverse of that catalyzed by the TCA enzyme citrate synthase except it requires the energy of ATP hydrolysis to drive it forward. The resultant oxaloacetate is converted to malate by malate dehydrogenase (MDH). The malate produced by this pathway can undergo oxidative decarboxylation by malic enzyme. The coenzyme for this reaction is NADP+-generating NADPH. The advantage of this series of reactions for converting mitochondrial acetyl-CoA into cytoplasmic acetyl-CoA is that the NADPH produced by the malic enzyme reaction can be a major source of reducing cofactor for the FAS activities

Acetyl-CoA Is Transported Out of the Mitochondria in Order to Serve