The structure of human phosphoglucose isomerase complexed with a transition-state analogue.

Phosphoglucose isomerase (PGI) is a workhorse enzyme of carbohydrate metabolism that interconverts glucose 6-phosphate and fructose 6-phosphate. Outside the cell, however, the protein appears to function as a cytokine. A crystal structure of human PGI bound with 5-phosphoarabinonate, a strong inhibitor that mimics the cis-enediol(ate) intermediate of the reaction, has been determined at 2.5 A resolution. The structure helps to confirm the assignment of Glu357 as the base catalyst in the isomerase reaction.