FIG 3 .

Activities of PBP6b and PBP5. (A) Purified PBP6b and PBP5 (2.7 µg) were analyzed by SDS-PAGE and Coomassie staining. (B) Increased Bocillin binding of PBP6b at pH 5.0. Purified PBP6b was incubated with the fluorescent penicillin derivative Bocillin for different time periods at 37°C and pH 5.0 or pH 7.5. The intensities of the fluorescence signals were quantified with ImageJ and are given relative to the value at pH 5.0 (45 min). (C) Activity of PBP6b and PBP5 against pentapeptide-rich PG from E. coli CS703-1 at pH 7.5 or 5.0. PG was incubated with different concentrations of PBP6b and PBP5, followed by digestion with cellosyl, reduction, and muropeptide analysis. Only changes in the main substrate (Penta, TetraPenta) and product (Tetra, TetraTetra) muropeptides are summarized. Representative chromatograms are shown in Fig. S3 and S4 in the supplemental material. The values are means ± standard deviations (SD) of the results of 3 independent experiments.