Fig. 4. Identification of isotope-labeled metabolites using UHPLC-HR-MS.

a Extracted ion chromatograms (EIC, Left) and the isotopic distributions (Right) of glutamine from E. diaphana incubated with ¹³C₆-glucose and ¹⁵N-ammonium (Top) and the corresponding glutamine standard (Bottom). The inset corresponds to a zoom of the area in which different isotopologue compositions of glutamine (dashed box) were identified using HR-MS. The gray ball and square indicate ¹²C atom and ¹⁴N atom, respectively; the red ball indicates ¹³C atom, the blue square indicates ¹⁵N, and the number of carbon and nitrogen atoms are inserted in the corresponding shapes. b Metabolic footprinting of stable isotopes in the three selected cnidarian species. The proposed ¹³C and ¹⁵N isotope labeling is indicated as red dots or written in blue color in the structural formulas. Heatmap color indicates the relative abundance of isotope-labeled metabolites (specifically summarized as ¹³C¹⁴N, ¹²C¹⁵N, and ¹³C¹⁵N) normalized to their non-labeled counterparts (¹²C¹⁴N). The isotopic forms of each compound shown in the heatmaps follow the same order as in the figure legend. The numeric values for heatmaps are included in Supplementary Data 5. Sym, symbiotic state; Apo, aposymbiotic state; *, undetectable metabolite.