Extended Data Figure 7: Measurement of CO₂ release rate from serine and glycine by combination of ¹⁴C- and ¹³C-labelling.

a, ¹⁴CO₂ release rate when cells are supplied with a medium with a trace amount of [3-¹⁴C]serine, [1-¹⁴C]glycine or [2-¹⁴C]glycine. b, Fraction of intracellular serine labelled in cells grown in DMEM media containing 0.4 mM [3-¹³C]serine in place of unlabelled serine. The residual unlabelled serine is presumably from de novo synthesis. c, Fraction of intracellular glycine labelled in cells grown in DMEM medium containing 0.4 mM [U-¹³C]glycine in place of unlabelled glycine. d, CO₂ release rates from serine C3, glycine C1 or C2. e, Potential alternative pathway to metabolize glycine or serine into CO₂, via pyruvate. f, Pyruvate labelling fraction after 48 h labelling with [U-¹³C]serine or [U-¹³C]glycine. The lack of labelling in pyruvate indicates that serine and glycine are not metabolized through this pathway. g, Knockdown of MTHFD2 or ALDH1L2 decreases CO₂ release from glycine C2. h, Knockdown of ALDH1L2 decreases the GSH/GSSG ratio. Mean ± s.d., n = 3.