<prompt> Which of the following is the major anaplerotic enzyme?Pyruvate carboxylaseAcetyl-CoA carboxylasePyruvate dehydrogenaseSuccinate dehydrogenase  <response>: Ans. aPyruvate carboxylase Anaplerotic gap-filling reactions are the reactions that replenish the depleted TCA cycle intermediates that were used up in the biosynthetic reactions. Oxaloacetate is the catalyst of TCA cycle. Thus, production of oxaloacetate is the major anaplerotic reaction. Intermediate Depleted used by Replenished by Oxaloacetate Amino Acid synthesis Pyruvate carboxylase - Major anaplerotic enzyme Succinyl-CoA Heme Synthesis From Propionyl-CoA by carboxylase and Methyl malonyl-CoA mutase Oxaloacetate, Fumarate Gluconeogenesis From Amino acids 