Phosphoglucose isomerase, glycolysis

The isomerization of D-glucose to D-fructose by way of an enediol intermediate is an important step in glycolysis, a complex process (11 steps) by which an organism converts glucose to chemical energy. The substrate is not glucose itself but its 6-phosphate ester. The enzyme that catalyzes the isomerization is called phosphoglucose isomerase. 

Conversion of glucose-6-phosphate to fructose-6-phosphate. During reaction 2 of glycolysis, the aldose glucose-6-phosphate is converted to the ketose fmctose-6-phosphate by phosphoglucose isomerase (PGI) in a readily reversible reaction ... 

The effect on 2,3-BPG metabolism varies (Fig. 18.2). If the disorder is proximal to the 2,3-BPG shunt (e.g. deficiencies of hexokinase, phosphoglucose isomerase and aldolase A), the flow of metabolites through glycolysis will be decreased and consequently the concentration of 2,3-BPG will fall. If the deficiency is distal to the 2,3-BPG shunt (e.g. pyruvate kinase deficiency), the concentration of 2,3-BPG will rise. 

---