Figure 3.

Tandem Q-TOF MS analysis of select muropeptides. Example of MS analysis of parent ions for muropeptides recovered from (A) mutanolysin (positive control) and (B) soluble RpfA digests of M. luteus peptidoglycan, by LC–MS as described in the legend of Fig. 2. C and D, tandem Q-TOF MS analysis of denoted parent ions from corresponding panels A and B. The blue spectral line in the MS spectrum of panel A denotes the ¹⁸O-containing isotope of the respective muropeptide. The monoisotopic masses (M + 2H)²⁺ are presented for each of the identified fragments.