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.

Quantitative 2H NMR at Natural Abundance Can Distinguish the Pathway Used for Glucose Fermentation by Lactic Acid Bacteria

“…2, step 2). This is in good agreement with the known leakiness of the intramolecular transfer during isomerization (9,18,19).…”

“…2 H NMR Spectroscopy-The 2 H NMR spectra were recorded with a Brucker DPX 400 spectrometer operating at 61.4 MHz and fitted with a 19 F field frequency locking device. The T 1 values were measured by using an inversion recovery sequence with 12 inversion time values ranging from 5 ms to 6 s and calculated using the T 1 calculation software provided.…”

Evidence for Transaldolase Activity in the Isolated Heart Supplied with [U-13C3]Glycerol

“…First, 2 H incorporation at the level of mannose 6-phosphate isomerase (F6P 7 mannose 6-phosphate) can lead to 2 H enrichment of H1 position of glucose (33). The other possibility is intramolecular exchange of 1 H in position 1 of F6P with 2 H in position 2 of G6P (34). In contrast to earlier reports (1-2), we found that oxidation of glycerol in the citric acid cycle did not contribute significantly to energy production using a perfusion medium containing physiological amounts of other unlabeled substrates.…”

Effets des sels de terres rares sur quelques phosphates dérivés des metabolites de la glycolyse

“…Les transferts de protons accompagnant les diffkrentes Ctapes de cette biotransformation suscitent encore de nombreux travaux (1)(2)(3)(4). I1 en est ainsi par exemple de l'isomerisation du glucose-6-phosphate (G-6P) en fructose-6-phosphate (F-6P) :…”

“…Le proton introduit en position pro-R provient a la fois du milieu et d'un transfert intramoltculaire (3,4). On ignore cependant avec certitude dans quelle proportion et quels sont les facteurs susceptibles de la modifier.…”