Figure 6.
Uptake of the β-lactam antibiotic nitrocefin by E. coli CE1265 cells expressing NalPβ variants. CE1265 (pPU361) and CE1265 (pPU363) express NalPβ and NalPβΔhelix, respectively, both fused to the signal sequence of PhoE, and CE1265 (pJP29_U) expresses just the signal sequence of PhoE. (A) Western blot analysis with NalPβ antiserum of CE1265 cells expressing the NalPβ variants. Plasmids used are indicated above the lanes, and molecular weight markers on the left of the panel. Only the relevant part of the gel, showing that expression of NalPβΔhelix is much lower than that of NalPβ, is shown. (B) The rate of nitrocefin uptake mediated by the NalPβ variants in CE1265 is given in nmol/min/109 cells. Experiments were performed three times in triplicate, and the values given are the means and the standard deviation. Differences between CE1265 (pPU363) on the one hand and CE1265 (pPU361) and CE1265 (pJP29_U) on the other hand were statistically significant (P<0.005).