Phosphglucoisomerase catalyzes the interconversion of glucose-6-phosphate (G6P) and fructose-6-phosphate (F6P).
This reaction, which is also the second step of glycolysis and the next to last step of gluconeogenesis, proceeds via an enediol intermediate (see here) and is readily reversible. The effect of transferring the carbonyl oxygen from carbon 1 to carbon 2 is that the hydroxyl group generated at carbon 1 can be readily phosphorylated.
Previous step of glycolysis / Next step of glycolysis
1. RasMol Image of Phosphoglucoisomerase (slow)
= +1.7 kJ/mol)