Figure 1.
[13C6]Glucose is more efficiently incorporated into purine rings than D2-Gly regardless of the MYC status. PC9 (a and c) and A549 (b and d) cells under control (CTL) or MYC suppression (siMYC) conditions were cultured in media containing [13C6]glucose and 2H2 (D2)-Gly and then analyzed by UHR-FTMS for 13C and D fractional enrichment in nucleotides and amino acids. The fractional 13C enrichment in the purine rings (Ring) of ATP and GTP was calculated by summing the 13C fraction of the 13C1–4 and 13C6–8 or 13C6–9 isotopologues, whereas the 13C and D fractional enrichment for Gly was obtained by summing the fraction of all labeled species. Schematics of the contributions of metabolic pathways to purine biosynthesis are shown in the middle panel. Black circle, 12C; red circle, 13C; and gray circle, 14N, D 2H in green; encircled 1 and encircled 2 refer, respectively, to direct and indirect routes of glycine incorporation into purines. a and b, fractional enrichment of 13C and D in purine rings (ATP and GTP). c and d, fractional enrichment of Gly isotopologues. Values are means ± S.E., n = 3. [13C6]Glucose was more efficiently incorporated into ATP and GTP than D2-Gly under both control and siMYC conditions. In addition, glucose-13C enrichment in ATP and GTP was strongly attenuated by MYC suppression in PC9 cells (**, t = 7.603, p = 0.006 for ATP, and t = 6.718, p = 0.0026 for GTP) but much less so in A549 cells (*, t = 3.162, p = 0.034 for ATP, and t = 1.109, p = 0.33 for GTP). MYC suppression had insignificant effects on [13C2]Gly and D-Gly isotopologue distribution (c and d; p > 0.05).