Fig. 4
From: Serine synthesis and catabolism in starved lung cancer and primary bronchial epithelial cells
Intracellular serine and glycine derived from exogenous serine and glycine supplied at high or low concentrations. Uniformly 13C labeled serine or glycine were used in A549 cells at high or low concentrations as tracers in media containing high or low glucose. A Enrichment (top) and total abundance normalized to protein (bottom) of serine and glycine. For the statistical analysis of enrichment the most informative isotopologue (##) was used. For abundance data, statistical analysis was performed on total metabolite abundance. B Enrichment ratios of (fully labeled) glycine M + 2 fractions normalized to (fully labeled) serine M + 3 and labeled serine (sum of M + 1, M + 2 and M + 3) fractions normalized to (fully labeled) glycine M + 2, respectively. A-B Results are shown as mean ± SEM from four independent experiments. Group comparisons were performed using Two-way ANOVA with Tukey post-hoc analysis. *P < 0.05; **P < 0.01; ***P < 0.001; n.s., not significant; # versus high glucose conditions. Ser/Gly, serine/glycine; C Summary of contributions from serine to glycine and vice versa, based on ratios shown in B. D Serine and glycine interconversion by SHMT. Filled circles represent 13C. meTHF; 5,10-methylene tetrahydrofolate