Modified C-terminal peptides identified from CPG70 tryptic digests using the Orbitrap MS with and without the inclusion of 0.2 M glycine in the growth medium.

a The delta mass is the observed mass minus the observed mass of the unmodified (water-cleaved) peptide (KAEDYIEVILDD, 1421.6930 Da). With the exception of the glycine-modified peptide, all observed masses are taken from the untreated sample. b The best match is the metabolite most closely matching the accurate delta mass value using the Metlin database (see Methods). In every case, the best match was a peptide or amino acid. For peptides, the order of amino acids was inferred from the MS/MS data, with the order of bracketed amino acids being uncertain. The mass error (in ppm) associated with this search is provided in the next column. c The intensity of the strongest MS peak, relative to the unmodified reference peak for the untreated sample. The values for the glycine-treated sample are provided in the next column. CPG70 was purified from W50ABK*WbaP.