Extracted ion chromatogram in the positive mode of the peptidoglycan precursors A. balhimycina wild type and vanHAXAbmutant. D-Lac: Peak of the pentapeptideprecursor ending on d-Ala–d-Lac with m/z of 1194. D-Ala: Peak of the pentapeptide precursor ending on d-Ala–d-Lac with m/z of 1193.