Modelling of isotopic discrimination in intact cells.
A mathematical model is designed for the metabolism of D-glucose in erythrocytes under conditions in which the flux through the pentose phosphate pathway accounts for either 5% or 75% of the rate of D-glucose phosphorylation, as indeed observed in the absence or presence of menadione. This model allows to compare the fate of D-[1-1H]glucose and D-[1-2H]glucose, taking into account the isotopic discrimination towards the deuterated hexose in the reactions catalyzed by phosphoglucoisomerase and glucose-6-phosphate dehydrogenase. The study of this model is extended to the fate of tracer amounts of either D-[1-14C]glucose, D-[U-14C]glucose or D-[1-3H]glucose mixed with non-radioactive D-[1-1H]glucose or D-[1-2H]glucose. The fates of D-[1-14C, 1-2H]glucose and D-[U-14C, 1-2H]glucose in this model are also examined. A fair agreement between the data derived from the mathematical model and prior experimental findings is observed, at least as far as the fate of 14C-labelled D-glucose is concerned. The present study illustrates, therefore, the mechanism by which unequal isotopic discrimination in different enzymatic reactions may cause severe misjudgment of metabolic flow when using deuterated and/or tritiated D-glucose as substitute and/or tracer for the protonated hexose.
Malaisse
W J
WJ
Laboratory of Experimental Medicine, Brussels Free University, Belgium.
D001786:Blood Glucose / Q000378:metabolism*; D002250:Carbon Radioisotopes; D003903:Deuterium; D004912:Erythrocytes / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008433:Mathematics; D008954:Models, Biological; D010427:Pentose Phosphate Pathway; D010766:Phosphorylation; D011865:Radioisotope Dilution Technique; D014316:Tritium
D001786:Blood Glucose; D002250:Carbon Radioisotopes; D014316:Tritium; D003903:Deuterium