Quantitative analysis of carbon-13 and

the metabolic fate of enriched [1-13C] glucose in rat C6 glioma cells was followed by 13C and 1H NMR techniques. The absolute and specific enrichments of glutamate were evaluated, and metabolic fluxes through the tricarboxylic acid (TCA) cycle were calculated. Results indicate that glucose derived carbon-13 isotope enter the TCA cycle via two pathways: the pyruvate dehydrogenase and the pyruvate carboxylase, leading to unequal distribution of carbon-13 isotope on glutamate carbon positions