Phosphoenolpyruvate phosphoryl-transfer potential

Figure 5.5 The coupled reaction in which ATP supplies the phosphoryl group for glucose-6-phosphate synthesis in contrast, phosphoenolpyruvate has a phosphoryl-transfer potential sufficiently elevated to enable it to donate its phosphoryl group to ADP, generating ATP.

In the next reaction, an enol is formed by the dehydration of 2-phosphoglycerate. Enolase catalyzes the formation of phosphoenolpyruvate (PEP). This dehydration markedly elevates the transfer potential of the phosphoryl group. An enol phosphate has a high phosphoryl-transfer potential, whereas the phosphate ester, such as 2-phosphoglycerate, of an ordinary alcohol has a low one. The A G° of the hydrolysis of a phosphate ester of an ordinary alcohol is -3 kcal mofi (-13 kJ mol i), whereas that of phosphoenolpyruvate is -14.8 kcal mofi (- 62 kJ mofi). Why does phosphoenolpyruvate have such a high phosphoryl-transfer potential The phosphoryl group traps the molecule in its unstable enol form. 

Why does phosphoenolpyruvate have such a high phosphoryl-transfer potential The phosphoryl group traps the molecule in its unstable enol form. When the phosphoryl group has been donated to ATP, the enol undergoes a conversion into the more stable ketone-—namely, pyruvate. 

In the next reaction, an enol is formed by the dehydration of 2-phosphoglycerate. Enolase catalyzes the formation of phosphoenolpyruvate (PEP). This dehydration markedly elevates the transfer potential of the phosphoryl group. An enol phosphate has a high phosphoryl-transfer potential. 

The first step in gluconeogenesis is the carboxylation of pyruvate to form oxaloacetate at the expense of a molecule of ATP. Then, oxaloacetate is de-carboxylated and phosphorylated to yield phosphoenolpyruvate, at the expense of the high phosphoryl-transfer potential of GTP. Both of these reactions take place inside the mitochondria. 

In the second glycolytic reaction that generates a compound with high phosphoryl group transfer potential, enolase promotes reversible removal of a molecule of water from 2-phosphoglycerate to yield phosphoenolpyruvate (PEP) ... 

Explain the high phosphoryl group-transfer potential of phosphoenolpyruvate as it is displayed in the pyruvate kinase reaction. 

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