Nad pools and dehydrogenase activities although both pyruvate dehydrogenase and glyceraldehyde 3-phosphate dehydrogenase use nad+ as their electron acceptor, the two enzymes do not compete for the same cellular nad pool. why?

Glyceraldehyde 3-phosphate dehydrogenase is present in cytosol and pyruvate dehydrogenase is an enzyme present in the mitochondrial matrix.

Explanation:

Pyruvate dehydrogenase (PDH) is located in the mitochondria of eukaryotic cells and in the cytosol of prokaryotes. The enzyme catalyzes the oxidative decarboxylation of pyruvate into acetyl CoA. Glyceraldehyde 3-phosphate dehydrogenase is the enzyme of glycolysis and catalyzes oxidation and phosphorylation of glyceraldehyde 3-phosphate into 1,3 bisphosphoglycerate.

Therefore, pyruvate dehydrogenase uses the NAD pool of mitochondrial matrix while glyceraldehyde 3-phosphate dehydrogenase derives NAD from the NAD pool of cytosol. The inner mitochondrial membrane is impermeable for large molecules and charged particles. Therefore, spatial separation of the activities of two enzymes does not allow them to compete for the NAD pool.  

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