Figure 1.

Chromatograms of the MRM signal intensities derived from the y₈ ions from the analyte decapeptides of Stx2a (YNEDDTFTVK), Stx2c (YNENDTFTVK), Stx2e (YNEDNTFTVK), and Stx2g (YNGDNTFTVK). The samples are derived from sterile filtered TSB broths from Stx2a, Stx2c, Stx2e, or Stx2g producing Escherichia coli strains and analyzed by mass spectrometry. The signal from the natural abundance decapeptide (i) is from the toxin and is not normalized. The corresponding signal from the ¹⁵N-labeled decapeptide is from the added internal standard (ii) and is included to show the retention time of the analyte decapeptide and is normalized to 500 to allow the signal from the analyte decapeptide to be viewed on the same plot.