Uses the Same Enzymes as Glycolysis

Conversion of Phosphoenolpyruvate to Fructose-1,6-bisphosphate Uses the Same Enzymes as Glycolysis 

The interconversions of the phosphorylated three-carbon acids—phosphenolpyruvate, glycerate-2-phosphate, and glycerate-3-phosphate—have already been discussed in this chapter. This pool is linked to the fructose-1,6-bisphos- 

Fructose-bisphosphate Phosphatase Converts Fructose-1,6-bisphosphate to Fructose-6-phosphate 

Fructose-1,6-bisphosphate is converted to fructose-6-phos-phate by hydrolysis of the phosphoryl ester bond at C-l in a reaction catalyzed by fructose bisphosphate phosphatase. The standard free energy change for this reaction is about —4 keal/mol, corresponding to an equilibrium constant of about 103. Thus, the two conversions (the phosphorylation of fructose-6-phosphate to form fructose 1,6-bisphosphate with ATP as the phosphate donor, and the hydrolysis of fructose-bisphosphate to form fructose-6-phosphate) are both thermodynamically favored under any conditions that are likely to exist in a living cell. These two reactions constitute a pseudocycle and, consistent with the principles enunciated in the previous chapter, the pathways have evolved so the number of ATP-to-ADP conversions is greater in one direction than in the other. 

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Gluconeogenesis Consumes ATP Conversion of Pyruvate to Phosphoenolpyruvate Requires Two High Energy Phosphates Conversion of Phosphoenolpyruvate to Fructose-1,6-bisphosphate Uses the Same Enzymes as Glycolysis... 

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