Extended Data Fig. 6: 13C6-Leu tracing distinguishes Leu- and Ile-conjugates that share identical MS/MS fragmentation.
From: C. elegans as a model for inter-individual variation in metabolism
a, Schematic of 13C6-Leu isotope-tracing experiment. Synchronized N2 and hphd-1(ok3580) animals were supplemented with Leu or 13C6-Leu and analysed for isotopic enrichment of metabolites of interest. b, EICs (negative ion mode) for m/z 202.1085 and 208.1291, corresponding to C9H16NO4- and 13C6-C9H16NO4-, from exo-metabolome extracts of N2 and hphd-1(ok3580). Red dashed lines highlight metabolites with 13C6-enrichment, corresponding to 3HP- and N-lactoyl Leu conjugates. Y-axis for m/z 208.1291 EIC is scaled 10-fold to more clearly show traces for labelled features. Isotopic labelling is highlighted with green shading in the shown compound structures. c, EIC for m/z 202.1085 (negative ion mode), corresponding to C9H16NO4-, from exo-metabolome extracts of N2 and the three wild strains. d, MS/MS fragmentation for metabolites A-F in (c). Metabolites A and B have near-identical MS/MS spectra, that differ significantly from the near-identical MS/MS spectra of metabolites C, D, E, and F. Based on isotopic labelling and MS/MS fragmentation data, A and B were assigned as 3HP-Ile and 3HP-Leu, respectively. The remaining four metabolites represent diastereomers of N-lactoyl-Ile and -Leu, with the later-eluting metabolite of each pair assigned as N-lactoyl-Leu based on isotopic enrichment (see panel b).
