Fig. 8.

OmpT activity in isolated outer membrane proteins of E. coli. Outer membrane proteins were isolated from a 40-mL culture of cells at A_{600 nm}=0.5 as described in the Materials and Methods and resuspended in 1 mL of assay buffer. A volume of 100 µL of protein solution was added to the Abz-Ala-Arg-Arg-Ala-Tyr(NO₂)-NH₂ substrate to a final substrate concentration of 0.16 mM. Fluorescence was recorded over 5 h at 37 °C in intervals of 5 min with an excitation wavelength of 320 nm and an emission wavelength of 420 nm. Designations: outer membrane proteins from OmpT-positive E. coli UT2300 cells with substrate (■), and without substrate (▲); outer membrane proteins from OmpT-negative E. coli UT5600 cells with substrate (■), and without substrate (▲)