Question

Consider the reaction catalyzed by the glycolytic enzyme pyruvate kinase.

Is this reaction simply reversed in the gluconeogenic pathway? Carefully describe the chemical reaction(s), enzyme(s) involved, and bioenergetics of the "reverse" of the pyruvate kinase reaction; in other words, how does pyruvate get converted back into phosphoenolpyruvate when gluconeogenesis is upregulated?

Answer 1

The enzyme pyruvate kinase is responsible for the conversion of Phosphoenolpyruvate(PEP) to pyruvate as the final step of glycolysis, thereby releasing 2 molecules of ATP(Adenosine triphosphate) along with the formation of Pyruvate.

Gluconeogenesis is considered to be the reverse of Glycolysis. However, the reactions are not completely identical. That is because if the glycolysis were to completely reverse for the formation of new glucose(gluconeogenesis), then the body will have to use too much energy, making the process unfruitful. Therefore, some steps are different from glycolysis in order to achieve gluconeogenesis with proper utilization of energy molecules. The first step in Gluconeogenesis involves the conversion of pyruvate to oxaloacetate and then to PEP with the help of enzymes pyruvate carboxylase and PEP carboxykinase respectively. Also, ATP is converted to ADP and GTP is converted to GDP. (2 molecules)