Phosphoenolpyruvate in gluconeogenesis

The conversion of pyruvate to phosphoenolpyruvate in gluconeogenesis takes place in two steps. The first step is the reaction of pyruvate and carbon dioxide to give oxaloacetate. This step requires energy, which is available from the hydrolysis of ATP. 

The equilibrium of pyruvate kinase is also strongly in the direction of glycolysis, because the immediate product of the reaction is enolpyruvate, which is chemically unstable. As shown in Figure 5.31, enolpyruvate undergoes a non-enzymic reaction to yield pyruvate. This means that little of the product of the enzymic reaction is available to undergo the reverse reaction in the direction of gluconeogenesis. The conversion of pyruvate to phosphoenolpyruvate in gluconeogenesis is discussed in section 5.7. 

---