Phosphoglucoisomerase-catalyzed interconversion of hexose phosphates. Study by 13C NMR of proton and deuteron...

The exchange of protons and deuterons by phosphoglucoisomerase during the single passage conversion of D-[2-13C,1-2H]fructose 6-phosphate in H2O or D-[2-13C]fructose 6-phosphate in D2O to D-[2-13C]glucose 6-phosphate, as coupled with the further generation of 6-phospho-D-[2-13C]gluconate in the presence of excess glucose-6-phosphate dehydrogenase was investigated by 13C NMR spectroscopy of the latter metabolite. In H2O, the intramolecular deuteron transfer from the C1 of D-fructose 6-phosphate to the C2 of D-glucose 6-phosphate amounted to 65%, a value only slightly lower than the 72% intramolecular proton transfer in D2O. Both percentages, especially the latter one, were lower than those previously recorded during the single passage conversion of D-[1-13C,2-2H]glucose 6-phosphate in H2O or D-[1-13C]glucose 6-phosphate in D2O to D-fructose 6-phosphate and then to D-fructose 1,6-bisphosphate. These differences indicate that the sequence of interactions between the hexose esters and the binding sites of phosphoglucoisomerase is not strictly in mirror image during, respectively, the conversion of the aldose phosphate to ketose phosphate and the opposite process.