Isotopic discrimination between D-[1-~(13)C]fructose and D-[2-~(13)C]fructose in rat liver cells

摘要

When liver cells from either normal or hereditarily diabetic rats are exposed to ~(13)C-enriched D-fructose (10 mM) and unlabelled D-glucose (also 10 mM) in the presence of D_2O, the output of ~(13)C-enriched D-glucose generated from D-[1-~(13)C]fructose is significantly lower than that from D-[2-~(13)C]fructose. This coincides with a higher generation of ~(13)C-enriched L-lactate and L-alanine from D-[1-~(13)C]fructose, as compared to D-[2-~(13)C]fructose. In absolute terms, the mean paired difference in the output of ~(13)C-enriched D-glucose generated from D-[1-~(13)C]fructose versus D-[2-~(13)C]fructose is not significantly different from the mean paired difference in the production of ~(13)C-enriched L-lactate and L-alanine from the same precursors, with an overall mean value of 7.01 +- 1.59 μmol (re = 8; P < 0.005). It is proposed that these findings indicate isotopic discrimination at the phosphoglucoisomerase level between ~(12)C and ~(13)C for the carbon atom in position 1 (as compared to that in position 2) of D-fructose 6-phosphate.