Figure 3.

13C Labeling in metabolites that report on glycolysis, Krebs cycle and uracil biosynthesis. The two-dimensional ¹H total correlation spectroscopy (TOCSY) spectrum was recorded at 18.8 T using an isotropic mixing time of 50 ms at a B₁ field strength of 8 kHz. The ¹³C satellites of glutamate and glutamate in reduced glutathione C2H-C4H are shown in cyan. This pattern corresponds to a mixture of species, namely where both ¹³C atoms are labeled in the same molecule plus ¹³C2¹²C4 and ¹²C2¹³C4. In contrast, the patterns for Ala (red) and Lac (green) shows only the ¹³C3¹³C2 plus ¹²C3¹²C2 pattern. Aspartate (red) shows a similar pattern as glutamate, reflecting scrambling through the Krebs cycle [8,10,11], and is the same as in U in UTP.