Extended Data Fig. 3: Related to Fig. 1: Absolute quantitation of kynurenine and tryptophan.

a-d, Quantitation using a known amount of isotope-labeled standards. a,b, Examples of extracted ion chromatograms showing reversed phase separation and mass spectrometry detection for kynurenine (10 ng) and D₄-kynurenine (50 ng); and tryptophan (10 ng) and ¹³C₁₁-tryptophan (50 ng). Each trace shows the ion signal at a given mass-to-charge ratio (m/z) as the compounds elute from an Atlantis T3 reversed phase column. c,d, Positive ion mass spectra of kynurenine and D₄-kynurenine; and tryptophan and ¹³C₁₁-tryptophan. e-h, Quantitation of kynurenine and tryptophan in an AC⁻ wild type sample. e,f, Examples of extracted ion chromatograms showing reversed phase separation and mass spectrometry detection for endogenous kynurenine and spiked D₄-kynurenine (50 ng); and endogenous tryptophan and spiked ¹³C₁₁-tryptophan (50 ng). Each trace shows the ion signal at a given mass-to-charge ratio (m/z) as the compounds elute from an Atlantis T3 reversed phase column. g,h, Positive ion mass spectra of endogenous kynurenine and D₄-kynurenine; and endogenous tryptophan and ¹³C₁₁-tryptophan. The normalization level (NL) indicates the intensity of the base peak for each spectrum.