1.Metabolism of 13C-enriched D-fructose in hepatocytes from Goto-Kakizaki rats.
Malaisse WJ1, Ladriere L, Verbruggen I, Willem R. Int J Mol Med. 2004 May;13(5):697-703.
This study aims at assessing the conversion of exogenous D-[1-13C]fructose, D-[2-13C]fructose or D-[6-13C]-fructose (10 mM) to 13C-enriched and either hydrogenated or deuterated D-glucose, L-lactate and L-alanine released by rat liver cells prepared from Goto-Kakizaki rats and incubated for 120 min in the presence of unlabelled D-glucose (also 10 mM) and D2O. The results of this study are relevant to the relative contribution of fructokinase and hexokinase isoenzyme to the phosphorylation of D-fructose, the capacity of D-glucose to confer to glucokinase positive cooperativity towards D-fructose, the circulation of D-fructose 6-phosphate in the pentose phosphate pathway, the regulation of the cytosolic NADD/NADH ratio, the respective fate of D-fructose-derived D-glyceraldehyde and dihydroxyacetone phosphate, the deuteration of fructose-derived glycolytic intermediates at the phosphoglucoisomerase, phosphomannoisomerase, enolase, pyruvate kinase and glutamate-alanine transaminase levels, and the unequal generation of L-[1-13C]lactate by cells exposed to D-[1-13C]fructose or D-[6-13C]fructose versus D-[2-13C]-fructose.
2.13C NMR study of the generation of C2- and C3-deuterated lactic acid by tumoral pancreatic islet cells exposed to D-[1-13C]-, D-[2-13C]- and D-[6-13C]-glucose in 2H2O.
Willem R1, Biesemans M, Kayser F, Malaisse WJ. Magn Reson Med. 1994 Mar;31(3):259-67.
Tumoral pancreatic islet cells of the RIN5mF line were incubated for 120 min in media prepared in 2H2O and containing D-[1-13C]glucose, D-[2-13C]glucose, and D-[6-13C]glucose. The generation of C2- and C3-deuterated lactic acid was assessed by 13C NMR. The interpretation of experimental results suggests that a) the efficiency of deuteration on the C1 of D-fructose 6-phosphate does not exceed about 47% and 4% in the phosphoglucoisomerase and phosphomannoisomerase reactions, respectively; b) approximately 38% of the molecules of D-glyceraldehyde 3-phosphate generated from D-glucose escape deuteration in the sequence of reactions catalyzed by triose phosphate isomerase and aldolase; and c) about 41% of the molecules of pyruvate generated by glycolysis are immediately converted to lactate, the remaining 59% of pyruvate molecules undergoing first a single or double back-and-forth interconversion with L-alanine. It is proposed that this methodological approach, based on high resolution 13C NMR spectroscopy, may provide novel information on the regulation of back-and-forth interconversion of glycolytic intermediates in intact cells as modulated, for instance, by enzyme-to-enzyme tunneling.
3.Generation of C3- and C2-deuterated L-lactic acid by human erythrocytes exposed to D-[1-13C]glucose, D-[2-13C]glucose and D-[6-13C]glucose in the presence of D2O.
Malaisse WJ1, Biesemans M, Willem R. Int J Biochem. 1994 May;26(5):697-702.
1. The generation of C2- and C3-deuterated L-lactate was monitored by 13C NMR in human erythrocytes exposed to D-[1-13C]glucose, D-[2-13C]glucose or D-[6-13C]glucose and incubated in a medium prepared in D2O. 2. The results suggested that the deuteration of the C1 of D-fructose 6-phosphate in the phosphoglucoisomerase reaction, the deuteration of the C1 of D-glyceraldehyde-3-phosphate in the sequence of reactions catalyzed by triose phosphate isomerase and aldolase and the deuteration of the C3 of pyruvate in the reaction catalyzed by pyruvate kinase were all lower than expected from equilibration with D2O. 3. Moreover, about 40% of the molecules of pyruvate generated by glycolysis apparently underwent deuteration on their C3 during interconversion of the 2-keto acid and L-alanine in the reaction catalyzed by glutamate-pyruvate transaminase. 4. The occurrence of the latter process was also documented in cells exposed to exogenous [3-13C]pyruvate.
4.Effects of D-glucose upon D-fructose metabolism in rat hepatocytes: A 13C NMR study.
Malaisse WJ1, Ladrière L, Verbruggen I, Willem R. Mol Cell Biochem. 2002 Dec;241(1-2):103-6.
Isolated hepatocytes from fed rats were exposed for 120 min to D-glucose (10 mM) and either D-[1-13C]fructose, D-[2-13C]fructose or D-[6-13C]fructose (also 10 mM) in the presence of D2O. The identification and quantification of 13C-enriched D-fructose and its metabolites (D-glucose, L-lactate, L-alanine) in the incubation medium and the measurement of their deuterated isotopomers indicated, by comparison with a prior study conducted in the absence of exogenous D-glucose, that the major effects of the aldohexose were to increase the recovery of 13C-enriched D-fructose, decrease the production of 13C-enriched D-glucose, restrict the deuteration of the 13C-enriched isotopomers of D-glucose to those generated by cells exposed to D-[2-13C]fructose, and to accentuate the lesser deuteration of the C, (as compared to C5) of 13C-enriched D-glucose derived from D-[2-13C]fructose. The ratio between C2-deuterated and C2-hydrogenated L-lactate, as well as the relative amounts of the CH3-, CH2D-, CHD, and CD3- isotopomers of 13C-enriched L-lactate were not significantly different, however, in the absence or presence of exogenous D-glucose.