title: Phosphoglucoisomerase-catalyzed interconversion of hexose phosphates: isotopic discrimination between hydrogen and deuterium.
abstract: The discrimination between the isotopes of hydrogen in the reaction catalyzed by yeast phosphoglucoisomerase is examined by NMR, as well as by spectrofluorometric or radioisotopic methods. The monodirectional conversion of D-glucose 6-phosphate to D-fructose 6-phosphate displays a lower maximal velocity with D-[2-2H]glucose 6-phosphate than unlabelled D-glucose 6-phosphate, with little difference in the affinity of the enzyme for these two substrates. About 72% of the deuterium located on the C2 of D-[1-13C,2-2H]glucose 6-phosphate is transferred intramolecularly to the C1 of D-[1-13C,1-2H]fructose 6-phosphate. The velocity of the monodirectional conversion of D-[U-14C]glucose 6-phosphate (or D-[2-3H]glucose 6-phosphate) to D-fructose 6-phosphate is virtually identical in H2O and D2O, respectively, but is four times lower with the tritiated than 14C-labelled ester. In the monodirectional reaction, the intramolecular transfer from the C2 of D-[2-3H]glucose 6-phosphate is higher in the presence of D2O than H2O. Whereas prolonged exposure of D-[1-13C]glucose 6-phosphate to D2O, in the presence of phosphoglucoisomerase, leads to the formation of both D-[1-13C,2-2H]glucose 6-phosphate and D-[1-13C,1-2H]fructose 6-phosphate, no sizeable incorporation of dueterium from D2O on the C1 of D-[1-13C]fructose 1,6-bisphosphate is observed when the monodirectional conversion of D-[1-13C]glucose 6-phosphate occurs in the concomitant presence of phosphoglucoisomerase and phosphofructokinase. The latter finding contrasts with the incorporation of hydrogen from 1H2O or tritium from 3H2O in the monodirectional conversion of D-[2-3H]glucose 6-phosphate and unlabelled D-glucose 6-phosphate, respectively, to their corresponding ketohexose esters.
authors.affiliation: Laboratory of Experimental Medicine, Brussels Free University School of Medicine, Belgium.
authors.forename: W J
authors.initials: WJ
authors.lastname: Malaisse
authors.forename: F
authors.initials: F
authors.lastname: Malaisse-Lagae
authors.forename: V
authors.initials: V
authors.lastname: Liemans
authors.forename: R
authors.initials: R
authors.lastname: Ottinger
authors.forename: R
authors.initials: R
authors.lastname: Willem
mesh_terms: D002247:Carbon Isotopes; D055598:Chemical Phenomena; D002621:Chemistry; D003903:Deuterium; D005636:Fructosephosphates / Q000378:metabolism*; D019298:Glucose-6-Phosphate; D005956:Glucose-6-Phosphate Isomerase / Q000378:metabolism*; D005958:Glucosephosphates / Q000378:metabolism*; D006859:Hydrogen; D009682:Magnetic Resonance Spectroscopy; D008954:Models, Biological
chemical_list: D002247:Carbon Isotopes; D005636:Fructosephosphates; D005958:Glucosephosphates; D019298:Glucose-6-Phosphate; C027618:fructose-6-phosphate; D006859:Hydrogen; D003903:Deuterium; D005956:Glucose-6-Phosphate Isomerase