Reaction 2: Isomerization
The glucose-6-phosphate is changed into an isomer, fructose-6-phosphate.
This means that the number of atoms is unchanged, but their positions
This works because the ring forms may open to the chain form,
and then the aldehyde group on glucose is transformed to the
ketone group on fructose. The ring then closes to form the fructose-6-phosphate.
This reaction is catalyzed by phosphogluco- isomerase.