Phosphoglucoisomerase-catalyzed interconversion of hexose-phosphates. Isotopic discrimination between hydrogen and tritium.

The rate of conversion of D-glucose 6-phosphate to D-fructose 6-phosphate as catalyzed by yeast phosphoglucoisomerase is about fourfold lower when 3H, rather than 1H, is present on the C2 of D-glucose 6-phosphate. This difference appears to be due mainly to a change in maximal velocity, rather than affinity. Phosphoglucoisomerase also distinguishes between 1H and 3H in terms of either their intramolecular transfer from C2 to C1 or their incorporation from water on the C1 of D-fructose 6-phosphate.