FIG. 3.

SDS-PAGE analysis of E. coli porins. (A) Overexpression of OmpN porin in E. coli BL21(DE3)omp8. Membrane pellets were extracted with 3% octyl-POE as described in Materials and Methods. Protein samples (from 15 ml of culture) were applied to the gel without (−) or with (+) heat treatment for 10 min at 95°C in sample buffer. (B) Electrophoretic mobilities of purified porins (indicated at the top), which were used for functional analyses, represent monomers (high mobility) and trimers (low mobility). They were purified from E. coli outer membranes as described in the text. The protein samples (3 to 5 μg) were heated as described above. Lane M, molecular weight standard.