Figure 1.

Metabolic model for the synthesis of glycogen and triglyceride from glucose or fructose in the liver. The model includes glucose-6-phosphate oxidation by the pentose phosphate pathway (PPP) to provide NADPH for conversion of acetyl-CoA to fatty acyl-CoA via de novo lipogenesis. The ¹³C-enriched glucose and fructose precursors are highlighted in red and the sampled metabolites, glycogen and triglyceride, are highlighted in blue. The metabolite pools whose ¹³C and ²H enrichments are reported by the sampled metabolites, namely, glucose-6-P, triose-P (dihydroxyacetone phosphate and glyceraldehyde 3-phosphate) and lipogenic acetyl-CoA, are highlighted in boxes. Glycogen synthesis from glucose via glucose-6-P from gluconeogenic precursors, including pyruvate and triose-P sources, is also indicated (direct and indirect pathways, respectively). For simplicity, some metabolic intermediates, as well as ATP/ADP and NAD/NADH interconversions, are not shown. Abbreviations are as follows: DHAP—dihydroxyacetone phosphate; F-1-P—fructose-1-phosphate; F-6-P—fructose 6-phosphate; F-1,6-P₂—fructose-1,6-bisphosphate; G-6-P—glucose 6-phosphate; Gly—glyceraldehyde; Gly-3-P—glyceraldehyde 3-phosphate; OA—oxaloacetate; PEP—phophoenolpyruvate; Ru-5-P: ribulose-5-P.