Figure 3: Adaptation of ribose (RNA) synthesis via the pentose cycle of HepG2 cells to glucose or fructose treatment. Glucose (Gluc; 5 mM, middle dark bars) or fructose (Fruct; 5 mM, dark bars) was added to the baseline 4.5mM glucose (Cont; 4.5 mM glucose, white bars). Ten percent (0.5 mM) glucose was supplied in the form of [1,2-13C2]-D-glucose as the single metabolic tracer in each culture and replaced every 24-h for a total of 72 hours culture. A, 13C labeled ribose fraction as percent of total unlabeled ribose in cell pellets; B, Pellet ribose M+1 SÁΧ1−C4 (one 13C substitution, m/z 242 ion, electron impact ionization) of its 13C labeled fraction; C, Pellet ribose M+2 SÁΧ1−Χ4 (two 13C substitutions, m/z 242 fragment, electron impact ionization) of its 13C labeled fraction; D, Triose (glyceraldehyde-3P recycling) via transketolase as ribose as M+2 SÁΧ3−Χ6 (two 13C substitutions, m/z 217 fragment, electron impact ionization) of its 13C labeled fraction (n=3; *p < 0.05).